Add YAMA security module restrictions on ptrace(2).

Restrict ptrace(2) according to the default configurations of the YAMA security
module (mode 1), which is a common default among various Linux distributions.
The new access checks only permit the tracer to proceed if one of the following
conditions is met:

a) The tracer is already attached to the tracee.

b) The target is a descendant of the tracer.

c) The target has explicitly given permission to the tracer through the
PR_SET_PTRACER prctl.

d) The tracer has CAP_SYS_PTRACE.

See security/yama/yama_lsm.c for more details.

Note that these checks are added to CanTrace, which is checked for
PTRACE_ATTACH as well as some other operations, e.g., checking a process'
memory layout through /proc/[pid]/mem.

Since this patch adds restrictions to ptrace, it may break compatibility for
applications run by non-root users that, for instance, rely on being able to
trace processes that are not descended from the tracer (e.g., `gdb -p`). YAMA
restrictions can be turned off by setting /proc/sys/kernel/yama/ptrace_scope
to 0, or exceptions can be made on a per-process basis with the PR_SET_PTRACER
prctl.

Reported-by: syzbot+622822d8bca08c99e8c8@syzkaller.appspotmail.com
PiperOrigin-RevId: 359237723

13 files changed, 1447 insertions, 20 deletions

diff --git a/pkg/abi/linux/prctl.go b/pkg/abi/linux/prctl.go
index 391cfaa1c..41118c3b4 100644
--- a/pkg/abi/linux/prctl.go
+++ b/pkg/abi/linux/prctl.go
@@ -144,6 +144,11 @@ const (
 	// PR_MPX_DISABLE_MANAGEMENT disables kernel management of Memory
 	// Protection eXtensions (MPX) bounds tables.
 	PR_MPX_DISABLE_MANAGEMENT = 44
+
+	// PR_SET_PTRACER allows a specific process (or any, if PR_SET_PTRACER_ANY is
+	// specified) to ptrace the current task.
+	PR_SET_PTRACER     = 0x59616d61
+	PR_SET_PTRACER_ANY = -1
 )
 
 // From <asm/prctl.h>
diff --git a/pkg/abi/linux/ptrace.go b/pkg/abi/linux/ptrace.go
index 23e605ab2..db1c6a0d8 100644
--- a/pkg/abi/linux/ptrace.go
+++ b/pkg/abi/linux/ptrace.go
@@ -87,3 +87,9 @@ const (
 	PTRACE_O_EXITKILL        = 1 << 20
 	PTRACE_O_SUSPEND_SECCOMP = 1 << 21
 )
+
+// YAMA ptrace_scope levels from security/yama/yama_lsm.c.
+const (
+	YAMA_SCOPE_DISABLED   = 0
+	YAMA_SCOPE_RELATIONAL = 1
+)
diff --git a/pkg/sentry/fsimpl/proc/BUILD b/pkg/sentry/fsimpl/proc/BUILD
index 5196a2a80..d47a4fff9 100644
--- a/pkg/sentry/fsimpl/proc/BUILD
+++ b/pkg/sentry/fsimpl/proc/BUILD
@@ -75,6 +75,7 @@ go_library(
         "tasks_files.go",
         "tasks_inode_refs.go",
         "tasks_sys.go",
+        "yama.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
diff --git a/pkg/sentry/fsimpl/proc/tasks_sys.go b/pkg/sentry/fsimpl/proc/tasks_sys.go
index 25c407d98..fd7823daa 100644
--- a/pkg/sentry/fsimpl/proc/tasks_sys.go
+++ b/pkg/sentry/fsimpl/proc/tasks_sys.go
@@ -48,6 +48,9 @@ func (fs *filesystem) newSysDir(ctx context.Context, root *auth.Credentials, k *
 			"shmall":   fs.newInode(ctx, root, 0444, shmData(linux.SHMALL)),
 			"shmmax":   fs.newInode(ctx, root, 0444, shmData(linux.SHMMAX)),
 			"shmmni":   fs.newInode(ctx, root, 0444, shmData(linux.SHMMNI)),
+			"yama": fs.newStaticDir(ctx, root, map[string]kernfs.Inode{
+				"ptrace_scope": fs.newYAMAPtraceScopeFile(ctx, k, root),
+			}),
 		}),
 		"vm": fs.newStaticDir(ctx, root, map[string]kernfs.Inode{
 			"mmap_min_addr":     fs.newInode(ctx, root, 0444, &mmapMinAddrData{k: k}),
diff --git a/pkg/sentry/fsimpl/proc/yama.go b/pkg/sentry/fsimpl/proc/yama.go
new file mode 100644
index 000000000..aebfe8944
--- /dev/null
+++ b/pkg/sentry/fsimpl/proc/yama.go
@@ -0,0 +1,80 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package proc
+
+import (
+	"bytes"
+	"fmt"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+func (fs *filesystem) newYAMAPtraceScopeFile(ctx context.Context, k *kernel.Kernel, creds *auth.Credentials) kernfs.Inode {
+	s := &yamaPtraceScope{level: &k.YAMAPtraceScope}
+	s.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), s, 0644)
+	return s
+}
+
+// yamaPtraceScope implements vfs.WritableDynamicBytesSource for
+// /sys/kernel/yama/ptrace_scope.
+//
+// +stateify savable
+type yamaPtraceScope struct {
+	kernfs.DynamicBytesFile
+
+	// level is the ptrace_scope level.
+	level *int32
+}
+
+// Generate implements vfs.DynamicBytesSource.Generate.
+func (s *yamaPtraceScope) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	_, err := fmt.Fprintf(buf, "%d\n", atomic.LoadInt32(s.level))
+	return err
+}
+
+// Write implements vfs.WritableDynamicBytesSource.Write.
+func (s *yamaPtraceScope) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	if offset != 0 {
+		// Ignore partial writes.
+		return 0, syserror.EINVAL
+	}
+	if src.NumBytes() == 0 {
+		return 0, nil
+	}
+
+	// Limit the amount of memory allocated.
+	src = src.TakeFirst(usermem.PageSize - 1)
+
+	var v int32
+	n, err := usermem.CopyInt32StringInVec(ctx, src.IO, src.Addrs, &v, src.Opts)
+	if err != nil {
+		return 0, err
+	}
+
+	// We do not support YAMA levels > YAMA_SCOPE_RELATIONAL.
+	if v < linux.YAMA_SCOPE_DISABLED || v > linux.YAMA_SCOPE_RELATIONAL {
+		return 0, syserror.EINVAL
+	}
+
+	atomic.StoreInt32(s.level, v)
+	return n, nil
+}
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index ef4e934a1..43065b45a 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -282,6 +282,18 @@ type Kernel struct {
 	// If set to true, report address space activation waits as if the task is in
 	// external wait so that the watchdog doesn't report the task stuck.
 	SleepForAddressSpaceActivation bool
+
+	// Exceptions to YAMA ptrace restrictions. Each key-value pair represents a
+	// tracee-tracer relationship. The key is a process (technically, the thread
+	// group leader) that can be traced by any thread that is a descendant of the
+	// value. If the value is nil, then anyone can trace the process represented by
+	// the key.
+	//
+	// ptraceExceptions is protected by the TaskSet mutex.
+	ptraceExceptions map[*Task]*Task
+
+	// YAMAPtraceScope is the current level of YAMA ptrace restrictions.
+	YAMAPtraceScope int32
 }
 
 // InitKernelArgs holds arguments to Init.
@@ -382,6 +394,8 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 	k.monotonicClock = &timekeeperClock{tk: args.Timekeeper, c: sentrytime.Monotonic}
 	k.futexes = futex.NewManager()
 	k.netlinkPorts = port.New()
+	k.ptraceExceptions = make(map[*Task]*Task)
+	k.YAMAPtraceScope = linux.YAMA_SCOPE_RELATIONAL
 
 	if VFS2Enabled {
 		ctx := k.SupervisorContext()
@@ -425,7 +439,6 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 
 		k.socketsVFS2 = make(map[*vfs.FileDescription]*SocketRecord)
 	}
-
 	return nil
 }
 
diff --git a/pkg/sentry/kernel/ptrace.go b/pkg/sentry/kernel/ptrace.go
index cef58a590..c3980350a 100644
--- a/pkg/sentry/kernel/ptrace.go
+++ b/pkg/sentry/kernel/ptrace.go
@@ -16,6 +16,7 @@ package kernel
 
 import (
 	"fmt"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/marshal/primitive"
@@ -95,7 +96,11 @@ const (
 // checks for access mode PTRACE_MODE_ATTACH; otherwise, it checks for access
 // mode PTRACE_MODE_READ.
 //
-// NOTE(b/30815691): The result of CanTrace is immediately stale (e.g., a
+// In Linux, ptrace access restrictions may be configured by LSMs. While we do
+// not support LSMs, we do add additional restrictions based on the commoncap
+// and YAMA LSMs.
+//
+// TODO(gvisor.dev/issue/212): The result of CanTrace is immediately stale (e.g., a
 // racing setuid(2) may change traceability). This may pose a risk when a task
 // changes from traceable to not traceable. This is only problematic across
 // execve, where privileges may increase.
@@ -103,7 +108,7 @@ const (
 // We currently do not implement privileged executables (set-user/group-ID bits
 // and file capabilities), so that case is not reachable.
 func (t *Task) CanTrace(target *Task, attach bool) bool {
-	// "1. If the calling thread and the target thread are in the same thread
+	// "If the calling thread and the target thread are in the same thread
 	// group, access is always allowed." - ptrace(2)
 	//
 	// Note: Strictly speaking, prior to 73af963f9f30 ("__ptrace_may_access()
@@ -115,9 +120,57 @@ func (t *Task) CanTrace(target *Task, attach bool) bool {
 		return true
 	}
 
+	if !t.canTraceStandard(target, attach) {
+		return false
+	}
+
+	// YAMA only supported for vfs2.
+	if !VFS2Enabled {
+		return true
+	}
+
+	if atomic.LoadInt32(&t.k.YAMAPtraceScope) == linux.YAMA_SCOPE_RELATIONAL {
+		t.tg.pidns.owner.mu.RLock()
+		defer t.tg.pidns.owner.mu.RUnlock()
+		if !t.canTraceYAMALocked(target) {
+			return false
+		}
+	}
+	return true
+}
+
+// canTraceLocked is the same as CanTrace, except the caller must already hold
+// the TaskSet mutex (for reading or writing).
+func (t *Task) canTraceLocked(target *Task, attach bool) bool {
+	if t.tg == target.tg {
+		return true
+	}
+
+	if !t.canTraceStandard(target, attach) {
+		return false
+	}
+
+	// YAMA only supported for vfs2.
+	if !VFS2Enabled {
+		return true
+	}
+
+	if atomic.LoadInt32(&t.k.YAMAPtraceScope) == linux.YAMA_SCOPE_RELATIONAL {
+		if !t.canTraceYAMALocked(target) {
+			return false
+		}
+	}
+	return true
+}
+
+// canTraceStandard performs standard ptrace access checks as defined by
+// kernel/ptrace.c:__ptrace_may_access as well as the commoncap LSM
+// implementation of the security_ptrace_access_check() interface, which is
+// always invoked.
+func (t *Task) canTraceStandard(target *Task, attach bool) bool {
 	// """
-	// 2. If the access mode specifies PTRACE_MODE_FSCREDS (ED: snipped,
-	// doesn't exist until Linux 4.5).
+	// TODO(gvisor.dev/issue/260): 1. If the access mode specifies
+	// PTRACE_MODE_FSCREDS (ED: snipped, doesn't exist until Linux 4.5).
 	//
 	// Otherwise, the access mode specifies PTRACE_MODE_REALCREDS, so use the
 	// caller's real UID and GID for the checks in the next step. (Most APIs
@@ -125,7 +178,7 @@ func (t *Task) CanTrace(target *Task, attach bool) bool {
 	// historical reasons, the PTRACE_MODE_REALCREDS check uses the real IDs
 	// instead.)
 	//
-	// 3. Deny access if neither of the following is true:
+	// 2. Deny access if neither of the following is true:
 	//
 	// - The real, effective, and saved-set user IDs of the target match the
 	// caller's user ID, *and* the real, effective, and saved-set group IDs of
@@ -134,15 +187,12 @@ func (t *Task) CanTrace(target *Task, attach bool) bool {
 	// - The caller has the CAP_SYS_PTRACE capability in the user namespace of
 	// the target.
 	//
-	// 4. Deny access if the target process "dumpable" attribute has a value
+	// 3. Deny access if the target process "dumpable" attribute has a value
 	// other than 1 (SUID_DUMP_USER; see the discussion of PR_SET_DUMPABLE in
 	// prctl(2)), and the caller does not have the CAP_SYS_PTRACE capability in
 	// the user namespace of the target process.
 	//
-	// 5. The kernel LSM security_ptrace_access_check() interface is invoked to
-	// see if ptrace access is permitted. The results depend on the LSM(s). The
-	// implementation of this interface in the commoncap LSM performs the
-	// following steps:
+	// 4. The commoncap LSM performs the following steps:
 	//
 	// a) If the access mode includes PTRACE_MODE_FSCREDS, then use the
 	// caller's effective capability set; otherwise (the access mode specifies
@@ -188,6 +238,94 @@ func (t *Task) CanTrace(target *Task, attach bool) bool {
 	return true
 }
 
+// canTraceYAMALocked performs ptrace access checks as defined by the YAMA LSM
+// implementation of the security_ptrace_access_check() interface, with YAMA
+// configured to mode 1. This is a common default among various Linux
+// distributions.
+//
+// It only permits the tracer to proceed if one of the following conditions is
+// met:
+//
+// a) The tracer is already attached to the tracee.
+//
+// b) The target is a descendant of the tracer.
+//
+// c) The target has explicitly given permission to the tracer through the
+// PR_SET_PTRACER prctl.
+//
+// d) The tracer has CAP_SYS_PTRACE.
+//
+// See security/yama/yama_lsm.c:yama_ptrace_access_check.
+//
+// Precondition: the TaskSet mutex must be locked (for reading or writing).
+func (t *Task) canTraceYAMALocked(target *Task) bool {
+	if tracer := target.Tracer(); tracer != nil {
+		if tracer.tg == t.tg {
+			return true
+		}
+	}
+	if target.isYAMADescendantOfLocked(t) {
+		return true
+	}
+	if target.hasYAMAExceptionForLocked(t) {
+		return true
+	}
+	if t.HasCapabilityIn(linux.CAP_SYS_PTRACE, target.UserNamespace()) {
+		return true
+	}
+	return false
+}
+
+// Determines whether t is considered a descendant of ancestor for the purposes
+// of YAMA permissions (specifically, whether t's thread group is descended from
+// ancestor's).
+//
+// Precondition: the TaskSet mutex must be locked (for reading or writing).
+func (t *Task) isYAMADescendantOfLocked(ancestor *Task) bool {
+	walker := t
+	for walker != nil {
+		if walker.tg.leader == ancestor.tg.leader {
+			return true
+		}
+		walker = walker.parent
+	}
+	return false
+}
+
+// Precondition: the TaskSet mutex must be locked (for reading or writing).
+func (t *Task) hasYAMAExceptionForLocked(tracer *Task) bool {
+	allowed, ok := t.k.ptraceExceptions[t]
+	if !ok {
+		return false
+	}
+	return allowed == nil || tracer.isYAMADescendantOfLocked(allowed)
+}
+
+// ClearYAMAException removes any YAMA exception with t as the tracee.
+func (t *Task) ClearYAMAException() {
+	t.tg.pidns.owner.mu.Lock()
+	defer t.tg.pidns.owner.mu.Unlock()
+	tracee := t.tg.leader
+	delete(t.k.ptraceExceptions, tracee)
+}
+
+// SetYAMAException creates a YAMA exception allowing all descendants of tracer
+// to trace t. If tracer is nil, then any task is allowed to trace t.
+//
+// If there was an existing exception, it is overwritten with the new one.
+func (t *Task) SetYAMAException(tracer *Task) {
+	t.tg.pidns.owner.mu.Lock()
+	defer t.tg.pidns.owner.mu.Unlock()
+
+	tracee := t.tg.leader
+	tracee.ptraceYAMAExceptionAdded = true
+	if tracer != nil {
+		tracer.ptraceYAMAExceptionAdded = true
+	}
+
+	t.k.ptraceExceptions[tracee] = tracer
+}
+
 // Tracer returns t's ptrace Tracer.
 func (t *Task) Tracer() *Task {
 	return t.ptraceTracer.Load().(*Task)
@@ -358,7 +496,7 @@ func (t *Task) ptraceTraceme() error {
 		// returning nil here is correct.
 		return nil
 	}
-	if !t.parent.CanTrace(t, true) {
+	if !t.parent.canTraceLocked(t, true) {
 		return syserror.EPERM
 	}
 	if t.parent.exitState != TaskExitNone {
@@ -377,11 +515,11 @@ func (t *Task) ptraceAttach(target *Task, seize bool, opts uintptr) error {
 	if t.tg == target.tg {
 		return syserror.EPERM
 	}
-	if !t.CanTrace(target, true) {
-		return syserror.EPERM
-	}
 	t.tg.pidns.owner.mu.Lock()
 	defer t.tg.pidns.owner.mu.Unlock()
+	if !t.canTraceLocked(target, true) {
+		return syserror.EPERM
+	}
 	if target.hasTracer() {
 		return syserror.EPERM
 	}
@@ -459,6 +597,15 @@ func (t *Task) exitPtrace() {
 	}
 	// "nil maps cannot be saved"
 	t.ptraceTracees = make(map[*Task]struct{})
+
+	if t.ptraceYAMAExceptionAdded {
+		delete(t.k.ptraceExceptions, t)
+		for tracee, tracer := range t.k.ptraceExceptions {
+			if tracer == t {
+				delete(t.k.ptraceExceptions, tracee)
+			}
+		}
+	}
 }
 
 // forgetTracerLocked detaches t's tracer and ensures that t is no longer
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index c0ab53c94..36141dd09 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -403,6 +403,13 @@ type Task struct {
 	// ptraceEventMsg is protected by the TaskSet mutex.
 	ptraceEventMsg uint64
 
+	// ptraceYAMAExceptionAdded is true if a YAMA exception involving the task has
+	// been added before. This is used during task exit to decide whether we need
+	// to clean up YAMA exceptions.
+	//
+	// ptraceYAMAExceptionAdded is protected by the TaskSet mutex.
+	ptraceYAMAExceptionAdded bool
+
 	// The struct that holds the IO-related usage. The ioUsage pointer is
 	// immutable.
 	ioUsage *usage.IO
diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index f7765fa3a..ad59e4f60 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -694,7 +694,8 @@ func (t *Task) exitNotifyLocked(fromPtraceDetach bool) {
 		}
 		if t.parent != nil {
 			delete(t.parent.children, t)
-			t.parent = nil
+			// Do not clear t.parent. It may be still be needed after the task has exited
+			// (for example, to perform ptrace access checks on /proc/[pid] files).
 		}
 	}
 }
diff --git a/pkg/sentry/kernel/threads.go b/pkg/sentry/kernel/threads.go
index e9da99067..09d070ec8 100644
--- a/pkg/sentry/kernel/threads.go
+++ b/pkg/sentry/kernel/threads.go
@@ -55,7 +55,7 @@ const InitTID ThreadID = 1
 //
 // +stateify savable
 type TaskSet struct {
-	// mu protects all relationships betweens tasks and thread groups in the
+	// mu protects all relationships between tasks and thread groups in the
 	// TaskSet. (mu is approximately equivalent to Linux's tasklist_lock.)
 	mu sync.RWMutex `state:"nosave"`
 
diff --git a/pkg/sentry/syscalls/linux/sys_prctl.go b/pkg/sentry/syscalls/linux/sys_prctl.go
index a892d2c62..9890dd946 100644
--- a/pkg/sentry/syscalls/linux/sys_prctl.go
+++ b/pkg/sentry/syscalls/linux/sys_prctl.go
@@ -172,6 +172,24 @@ func Prctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 		}
 		return 1, nil, nil
 
+	case linux.PR_SET_PTRACER:
+		pid := args[1].Int()
+		switch pid {
+		case 0:
+			t.ClearYAMAException()
+			return 0, nil, nil
+		case linux.PR_SET_PTRACER_ANY:
+			t.SetYAMAException(nil)
+			return 0, nil, nil
+		default:
+			tracer := t.PIDNamespace().TaskWithID(kernel.ThreadID(pid))
+			if tracer == nil {
+				return 0, nil, syserror.EINVAL
+			}
+			t.SetYAMAException(tracer)
+			return 0, nil, nil
+		}
+
 	case linux.PR_SET_SECCOMP:
 		if args[1].Int() != linux.SECCOMP_MODE_FILTER {
 			// Unsupported mode.
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 1a492bca3..f871426f0 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -1814,6 +1814,7 @@ cc_binary(
         "@com_google_absl//absl/flags:flag",
         "@com_google_absl//absl/time",
         gtest,
+        "//test/util:capability_util",
         "//test/util:file_descriptor",
         "//test/util:fs_util",
         "//test/util:logging",
diff --git a/test/syscalls/linux/ptrace.cc b/test/syscalls/linux/ptrace.cc
index 13c19d4a8..d1d7c6f84 100644
--- a/test/syscalls/linux/ptrace.cc
+++ b/test/syscalls/linux/ptrace.cc
@@ -15,7 +15,9 @@
 #include <elf.h>
 #include <signal.h>
 #include <stddef.h>
+#include <sys/prctl.h>
 #include <sys/ptrace.h>
+#include <sys/socket.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/user.h>
@@ -30,6 +32,7 @@
 #include "absl/flags/flag.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "test/util/capability_util.h"
 #include "test/util/fs_util.h"
 #include "test/util/logging.h"
 #include "test/util/memory_util.h"
@@ -45,6 +48,49 @@ ABSL_FLAG(bool, ptrace_test_execve_child, false,
           "If true, run the "
           "PtraceExecveTest_Execve_GetRegs_PeekUser_SIGKILL_TraceClone_"
           "TraceExit child workload.");
+ABSL_FLAG(bool, ptrace_test_trace_descendants_allowed, false,
+          "If set, run the child workload for "
+          "PtraceTest_TraceDescendantsAllowed.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_pid, false,
+          "If set, run the child workload for PtraceTest_PrctlSetPtracerPID.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_any, false,
+          "If set, run the child workload for PtraceTest_PrctlSetPtracerAny.");
+ABSL_FLAG(bool, ptrace_test_prctl_clear_ptracer, false,
+          "If set, run the child workload for PtraceTest_PrctlClearPtracer.");
+ABSL_FLAG(bool, ptrace_test_prctl_replace_ptracer, false,
+          "If set, run the child workload for PtraceTest_PrctlReplacePtracer.");
+ABSL_FLAG(int, ptrace_test_prctl_replace_ptracer_tid, -1,
+          "Specifies the replacement tracer tid in the child workload for "
+          "PtraceTest_PrctlReplacePtracer.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_and_exit_tracee_thread, false,
+          "If set, run the child workload for "
+          "PtraceTest_PrctlSetPtracerPersistsPastTraceeThreadExit.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_and_exec_non_leader, false,
+          "If set, run the child workload for "
+          "PtraceTest_PrctlSetPtracerDoesNotPersistPastNonLeaderExec.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_and_exit_tracer_thread, false,
+          "If set, run the child workload for "
+          "PtraceTest_PrctlSetPtracerDoesNotPersistPastTracerThreadExit.");
+ABSL_FLAG(int, ptrace_test_prctl_set_ptracer_and_exit_tracer_thread_tid, -1,
+          "Specifies the tracee tid in the child workload for "
+          "PtraceTest_PrctlSetPtracerDoesNotPersistPastTracerThreadExit.");
+ABSL_FLAG(bool, ptrace_test_prctl_set_ptracer_respects_tracer_thread_id, false,
+          "If set, run the child workload for PtraceTest_PrctlSetPtracePID.");
+ABSL_FLAG(int, ptrace_test_prctl_set_ptracer_respects_tracer_thread_id_tid, -1,
+          "Specifies the thread tid to be traced in the child workload "
+          "for PtraceTest_PrctlSetPtracerRespectsTracerThreadID.");
+
+ABSL_FLAG(bool, ptrace_test_tracee, false,
+          "If true, run the tracee process for the "
+          "PrctlSetPtracerDoesNotPersistPastLeaderExec and "
+          "PrctlSetPtracerDoesNotPersistPastNonLeaderExec workloads.");
+ABSL_FLAG(int, ptrace_test_trace_tid, -1,
+          "If set, run a process to ptrace attach to the thread with the "
+          "specified pid for the PrctlSetPtracerRespectsTracerThreadID "
+          "workload.");
+ABSL_FLAG(int, ptrace_test_fd, -1,
+          "Specifies the fd used for communication between tracer and tracee "
+          "processes across exec.");
 
 namespace gvisor {
 namespace testing {
@@ -78,10 +124,10 @@ void RaiseSignal(int sig) {
   TEST_PCHECK(tgkill(pid, tid, sig) == 0);
 }
 
+constexpr char kYamaPtraceScopePath[] = "/proc/sys/kernel/yama/ptrace_scope";
+
 // Returns the Yama ptrace scope.
 PosixErrorOr<int> YamaPtraceScope() {
-  constexpr char kYamaPtraceScopePath[] = "/proc/sys/kernel/yama/ptrace_scope";
-
   ASSIGN_OR_RETURN_ERRNO(bool exists, Exists(kYamaPtraceScopePath));
   if (!exists) {
     // File doesn't exist means no Yama, so the scope is disabled -> 0.
@@ -99,6 +145,22 @@ PosixErrorOr<int> YamaPtraceScope() {
   return scope;
 }
 
+int CheckPtraceAttach(pid_t pid) {
+  int ret = ptrace(PTRACE_ATTACH, pid, 0, 0);
+  MaybeSave();
+  if (ret < 0) {
+    return ret;
+  }
+
+  int status;
+  TEST_PCHECK(waitpid(pid, &status, 0) == pid);
+  MaybeSave();
+  TEST_CHECK(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+  TEST_PCHECK(ptrace(PTRACE_DETACH, pid, 0, 0) == 0);
+  MaybeSave();
+  return 0;
+}
+
 TEST(PtraceTest, AttachSelf) {
   EXPECT_THAT(ptrace(PTRACE_ATTACH, gettid(), 0, 0),
               SyscallFailsWithErrno(EPERM));
@@ -111,10 +173,995 @@ TEST(PtraceTest, AttachSameThreadGroup) {
   });
 }
 
+TEST(PtraceTest, TraceParentNotAllowed) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) < 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  pid_t const child_pid = fork();
+  if (child_pid == 0) {
+    TEST_CHECK(CheckPtraceAttach(getppid()) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  ASSERT_THAT(child_pid, SyscallSucceeds());
+
+  int status;
+  ASSERT_THAT(waitpid(child_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+}
+
+TEST(PtraceTest, TraceNonDescendantNotAllowed) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) < 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    TEST_CHECK(CheckPtraceAttach(tracee_pid) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  EXPECT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+TEST(PtraceTest, TraceNonDescendantWithCapabilityAllowed) {
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_PTRACE)));
+  // Skip if disallowed by YAMA despite having CAP_SYS_PTRACE.
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) > 2);
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    TEST_PCHECK(CheckPtraceAttach(tracee_pid) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+TEST(PtraceTest, TraceDescendantsAllowed) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) > 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use socket pair to communicate tids to this process from its grandchild.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_trace_descendants_allowed",
+      "--ptrace_test_fd", std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const child_pid = fork();
+  if (child_pid == 0) {
+    // In child process.
+    TEST_PCHECK(close(sockets[1]) == 0);
+    pid_t const grandchild_pid = fork();
+    if (grandchild_pid == 0) {
+      // This test will create a new thread in the grandchild process.
+      // pthread_create(2) isn't async-signal-safe, so we execve() first.
+      execve(child_argv[0], child_argv, /* envp = */ nullptr);
+      TEST_PCHECK_MSG(false, "Survived execve to test child");
+    }
+    TEST_PCHECK(grandchild_pid > 0);
+    MaybeSave();
+
+    // Wait for grandchild. Our parent process will kill it once it's done.
+    int status;
+    TEST_PCHECK(waitpid(grandchild_pid, &status, 0) == grandchild_pid);
+    TEST_CHECK(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL);
+    MaybeSave();
+    _exit(0);
+  }
+  ASSERT_THAT(child_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  // We should be able to attach to any thread in the grandchild.
+  pid_t grandchild_tid1, grandchild_tid2;
+  ASSERT_THAT(read(sockets[1], &grandchild_tid1, sizeof(grandchild_tid1)),
+              SyscallSucceedsWithValue(sizeof(grandchild_tid1)));
+  ASSERT_THAT(read(sockets[1], &grandchild_tid2, sizeof(grandchild_tid2)),
+              SyscallSucceedsWithValue(sizeof(grandchild_tid2)));
+
+  EXPECT_THAT(CheckPtraceAttach(grandchild_tid1), SyscallSucceeds());
+  EXPECT_THAT(CheckPtraceAttach(grandchild_tid2), SyscallSucceeds());
+
+  // Clean up grandchild.
+  ASSERT_THAT(kill(grandchild_tid1, SIGKILL), SyscallSucceeds());
+
+  // Clean up child.
+  int status;
+  ASSERT_THAT(waitpid(child_pid, &status, 0),
+              SyscallSucceedsWithValue(child_pid));
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+}
+
+[[noreturn]] void RunTraceDescendantsAllowed(int fd) {
+  // Let the tracer know our tid through the socket fd.
+  pid_t const tid = gettid();
+  TEST_PCHECK(write(fd, &tid, sizeof(tid)) == sizeof(tid));
+  MaybeSave();
+
+  ScopedThread t([fd] {
+    // See if any arbitrary thread (whose tid differs from the process id) can
+    // be traced as well.
+    pid_t const tid = gettid();
+    TEST_PCHECK(write(fd, &tid, sizeof(tid)) == sizeof(tid));
+    MaybeSave();
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  });
+
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+TEST(PtraceTest, PrctlSetPtracerInvalidPID) {
+  // EINVAL should also be returned if PR_SET_PTRACER is not supported.
+  EXPECT_THAT(prctl(PR_SET_PTRACER, 123456789), SyscallFailsWithErrno(EINVAL));
+}
+
+TEST(PtraceTest, PrctlSetPtracerPID) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_prctl_set_ptracer_pid",
+      "--ptrace_test_fd", std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until tracee has called prctl.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(CheckPtraceAttach(tracee_pid) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerPID(int fd) {
+  ScopedThread t([fd] {
+    // Perform prctl in a separate thread to verify that it is process-wide.
+    TEST_PCHECK(prctl(PR_SET_PTRACER, getppid()) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(fd, "x", 1) == 1);
+    MaybeSave();
+  });
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+TEST(PtraceTest, PrctlSetPtracerAny) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_prctl_set_ptracer_any",
+      "--ptrace_test_fd", std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    TEST_PCHECK(close(sockets[1]) == 0);
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until tracee has called prctl.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(CheckPtraceAttach(tracee_pid) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerAny(int fd) {
+  ScopedThread t([fd] {
+    // Perform prctl in a separate thread to verify that it is process-wide.
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(fd, "x", 1) == 1);
+    MaybeSave();
+  });
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+TEST(PtraceTest, PrctlClearPtracer) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_prctl_clear_ptracer", "--ptrace_test_fd",
+      std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    TEST_PCHECK(close(sockets[1]) == 0);
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until tracee has called prctl.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_CHECK(CheckPtraceAttach(tracee_pid) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlClearPtracer(int fd) {
+  ScopedThread t([fd] {
+    // Perform prctl in a separate thread to verify that it is process-wide.
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+    TEST_PCHECK(prctl(PR_SET_PTRACER, 0) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set/cleared.
+    TEST_PCHECK(write(fd, "x", 1) == 1);
+    MaybeSave();
+  });
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+TEST(PtraceTest, PrctlReplacePtracer) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  pid_t const unused_pid = fork();
+  if (unused_pid == 0) {
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(unused_pid, SyscallSucceeds());
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe",
+      "--ptrace_test_prctl_replace_ptracer",
+      "--ptrace_test_prctl_replace_ptracer_tid",
+      std::to_string(unused_pid),
+      "--ptrace_test_fd",
+      std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until tracee has called prctl.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_CHECK(CheckPtraceAttach(tracee_pid) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+
+  // Clean up unused.
+  ASSERT_THAT(kill(unused_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(unused_pid, &status, 0),
+              SyscallSucceedsWithValue(unused_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlReplacePtracer(int new_tracer_pid, int fd) {
+  TEST_PCHECK(prctl(PR_SET_PTRACER, getppid()) == 0);
+  MaybeSave();
+
+  ScopedThread t([new_tracer_pid, fd] {
+    TEST_PCHECK(prctl(PR_SET_PTRACER, new_tracer_pid) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(fd, "x", 1) == 1);
+    MaybeSave();
+  });
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+// Tests that YAMA exceptions store tracees by thread group leader. Exceptions
+// are preserved even after the tracee thread exits, as long as the tracee's
+// thread group leader is still around.
+TEST(PtraceTest, PrctlSetPtracerPersistsPastTraceeThreadExit) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe",
+      "--ptrace_test_prctl_set_ptracer_and_exit_tracee_thread",
+      "--ptrace_test_fd", std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    TEST_PCHECK(close(sockets[1]) == 0);
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until the tracee thread calling prctl has terminated.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(CheckPtraceAttach(tracee_pid) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerPersistsPastTraceeThreadExit(int fd) {
+  ScopedThread t([] {
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+  });
+  t.Join();
+  // Indicate that thread setting the prctl has exited.
+  TEST_PCHECK(write(fd, "x", 1) == 1);
+  MaybeSave();
+
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+// Tests that YAMA exceptions store tracees by thread group leader. Exceptions
+// are preserved across exec as long as the thread group leader does not change,
+// even if the tracee thread is terminated.
+TEST(PtraceTest, PrctlSetPtracerPersistsPastLeaderExec) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_tracee", "--ptrace_test_fd",
+      std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until the tracee has exec'd.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(CheckPtraceAttach(tracee_pid) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunTracee(int fd) {
+  // Indicate that we have exec'd.
+  TEST_PCHECK(write(fd, "x", 1) == 1);
+  MaybeSave();
+
+  while (true) {
+    SleepSafe(absl::Seconds(1));
+  }
+}
+
+// Tests that YAMA exceptions store tracees by thread group leader. Exceptions
+// are cleared if the tracee process's thread group leader is terminated by
+// exec.
+TEST(PtraceTest, PrctlSetPtracerDoesNotPersistPastNonLeaderExec) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe", "--ptrace_test_prctl_set_ptracer_and_exec_non_leader",
+      "--ptrace_test_fd", std::to_string(sockets[0])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    TEST_PCHECK(close(sockets[1]) == 0);
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until the tracee has exec'd.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_CHECK(CheckPtraceAttach(tracee_pid) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerDoesNotPersistPastNonLeaderExec(int fd) {
+  ScopedThread t([fd] {
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+
+    ExecveArray const owned_child_argv = {
+        "/proc/self/exe", "--ptrace_test_tracee", "--ptrace_test_fd",
+        std::to_string(fd)};
+    char* const* const child_argv = owned_child_argv.get();
+
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  });
+  t.Join();
+  TEST_CHECK_MSG(false, "Survived execve? (main)");
+  _exit(1);
+}
+
+// Tests that YAMA exceptions store the tracer itself rather than the thread
+// group leader. Exceptions are cleared when the tracer task exits, rather than
+// when its thread group leader exits.
+TEST(PtraceTest, PrctlSetPtracerDoesNotPersistPastTracerThreadExit) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    pid_t tracer_tid;
+    TEST_PCHECK(read(sockets[0], &tracer_tid, sizeof(tracer_tid)) ==
+                sizeof(tracer_tid));
+    MaybeSave();
+
+    TEST_PCHECK(prctl(PR_SET_PTRACER, tracer_tid) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(sockets[0], "x", 1) == 1);
+    MaybeSave();
+
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe",
+      "--ptrace_test_prctl_set_ptracer_and_exit_tracer_thread",
+      "--ptrace_test_prctl_set_ptracer_and_exit_tracer_thread_tid",
+      std::to_string(tracee_pid),
+      "--ptrace_test_fd",
+      std::to_string(sockets[1])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerDoesNotPersistPastTracerThreadExit(
+    int tracee_tid, int fd) {
+  TEST_PCHECK(SetCapability(CAP_SYS_PTRACE, false).ok());
+
+  ScopedThread t([fd] {
+    pid_t const tracer_tid = gettid();
+    TEST_PCHECK(write(fd, &tracer_tid, sizeof(tracer_tid)) ==
+                sizeof(tracer_tid));
+
+    // Wait until the prctl has been set.
+    char done;
+    TEST_PCHECK(read(fd, &done, 1) == 1);
+    MaybeSave();
+  });
+  t.Join();
+
+  // Sleep for a bit before verifying the invalidation. The thread exit above
+  // should cause the ptrace exception to be invalidated, but in Linux, this is
+  // not done immediately. The YAMA exception is dropped during
+  // __put_task_struct(), which occurs (at the earliest) one RCU grace period
+  // after exit_notify() ==> release_task().
+  SleepSafe(absl::Milliseconds(100));
+
+  TEST_CHECK(CheckPtraceAttach(tracee_tid) == -1);
+  TEST_PCHECK(errno == EPERM);
+  _exit(0);
+}
+
+// Tests that YAMA exceptions store the tracer thread itself rather than the
+// thread group leader. Exceptions are preserved across exec in the tracer
+// thread, even if the thread group leader is terminated.
+TEST(PtraceTest, PrctlSetPtracerRespectsTracerThreadID) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    pid_t tracer_tid;
+    TEST_PCHECK(read(sockets[0], &tracer_tid, sizeof(tracer_tid)) ==
+                sizeof(tracer_tid));
+    MaybeSave();
+
+    TEST_PCHECK(prctl(PR_SET_PTRACER, tracer_tid) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(sockets[0], "x", 1) == 1);
+    MaybeSave();
+
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  // Allocate vector before forking (not async-signal-safe).
+  ExecveArray const owned_child_argv = {
+      "/proc/self/exe",
+      "--ptrace_test_prctl_set_ptracer_respects_tracer_thread_id",
+      "--ptrace_test_prctl_set_ptracer_respects_tracer_thread_id_tid",
+      std::to_string(tracee_pid),
+      "--ptrace_test_fd",
+      std::to_string(sockets[1])};
+  char* const* const child_argv = owned_child_argv.get();
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // This test will create a new thread in the child process.
+    // pthread_create(2) isn't async-signal-safe, so we execve() first.
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+[[noreturn]] void RunPrctlSetPtracerRespectsTracerThreadID(int tracee_tid,
+                                                           int fd) {
+  // Create a separate thread for tracing (i.e., not the thread group
+  // leader). After the subsequent execve(), the current thread group leader
+  // will no longer be exist, but the YAMA exception installed with this
+  // thread should still be valid.
+  ScopedThread t([tracee_tid, fd] {
+    pid_t const tracer_tid = gettid();
+    TEST_PCHECK(write(fd, &tracer_tid, sizeof(tracer_tid)));
+    MaybeSave();
+
+    // Wait until the tracee has made the PR_SET_PTRACER prctl.
+    char done;
+    TEST_PCHECK(read(fd, &done, 1) == 1);
+    MaybeSave();
+
+    ExecveArray const owned_child_argv = {
+        "/proc/self/exe", "--ptrace_test_trace_tid", std::to_string(tracee_tid),
+        "--ptrace_test_fd", std::to_string(fd)};
+    char* const* const child_argv = owned_child_argv.get();
+
+    execve(child_argv[0], child_argv, /* envp = */ nullptr);
+    TEST_PCHECK_MSG(false, "Survived execve to test child");
+  });
+  t.Join();
+  TEST_CHECK_MSG(false, "Survived execve? (main)");
+  _exit(1);
+}
+
+[[noreturn]] void RunTraceTID(int tracee_tid, int fd) {
+  TEST_PCHECK(SetCapability(CAP_SYS_PTRACE, false).ok());
+  TEST_PCHECK(CheckPtraceAttach(tracee_tid) == 0);
+  _exit(0);
+}
+
+// Tests that removing a YAMA exception does not affect a tracer that is already
+// attached.
+TEST(PtraceTest, PrctlClearPtracerDoesNotAffectCurrentTracer) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Use sockets to synchronize between tracer and tracee.
+  int sockets[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sockets), SyscallSucceeds());
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    TEST_PCHECK(close(sockets[1]) == 0);
+    TEST_PCHECK(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(sockets[0], "x", 1) == 1);
+    MaybeSave();
+
+    // Wait until tracer has attached before clearing PR_SET_PTRACER.
+    char done;
+    TEST_PCHECK(read(sockets[0], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(prctl(PR_SET_PTRACER, 0) == 0);
+    MaybeSave();
+    // Indicate that the prctl has been set.
+    TEST_PCHECK(write(sockets[0], "x", 1) == 1);
+    MaybeSave();
+
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+  ASSERT_THAT(close(sockets[0]), SyscallSucceeds());
+
+  std::string mem_path = "/proc/" + std::to_string(tracee_pid) + "/mem";
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    // Wait until tracee has called prctl, or else we won't be able to attach.
+    char done;
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    TEST_PCHECK(ptrace(PTRACE_ATTACH, tracee_pid, 0, 0) == 0);
+    MaybeSave();
+    // Indicate that we have attached.
+    TEST_PCHECK(write(sockets[1], &done, 1) == 1);
+    MaybeSave();
+
+    // Block until tracee enters signal-delivery-stop as a result of the
+    // SIGSTOP sent by PTRACE_ATTACH.
+    int status;
+    TEST_PCHECK(waitpid(tracee_pid, &status, 0) == tracee_pid);
+    MaybeSave();
+    TEST_CHECK(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+    MaybeSave();
+
+    TEST_PCHECK(ptrace(PTRACE_CONT, tracee_pid, 0, 0) == 0);
+    MaybeSave();
+
+    // Wait until tracee has cleared PR_SET_PTRACER. Even though it was cleared,
+    // we should still be able to access /proc/[pid]/mem because we are already
+    // attached.
+    TEST_PCHECK(read(sockets[1], &done, 1) == 1);
+    MaybeSave();
+    TEST_PCHECK(open(mem_path.c_str(), O_RDONLY) != -1);
+    MaybeSave();
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
+TEST(PtraceTest, PrctlNotInherited) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) != 1);
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+
+  // Allow any ptracer. This should not affect the child processes.
+  ASSERT_THAT(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY), SyscallSucceeds());
+
+  pid_t const tracee_pid = fork();
+  if (tracee_pid == 0) {
+    while (true) {
+      SleepSafe(absl::Seconds(1));
+    }
+  }
+  ASSERT_THAT(tracee_pid, SyscallSucceeds());
+
+  pid_t const tracer_pid = fork();
+  if (tracer_pid == 0) {
+    TEST_CHECK(CheckPtraceAttach(tracee_pid) == -1);
+    TEST_PCHECK(errno == EPERM);
+    _exit(0);
+  }
+  ASSERT_THAT(tracer_pid, SyscallSucceeds());
+
+  // Clean up tracer.
+  int status;
+  ASSERT_THAT(waitpid(tracer_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Clean up tracee.
+  ASSERT_THAT(kill(tracee_pid, SIGKILL), SyscallSucceeds());
+  ASSERT_THAT(waitpid(tracee_pid, &status, 0),
+              SyscallSucceedsWithValue(tracee_pid));
+  EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)
+      << " status " << status;
+}
+
 TEST(PtraceTest, AttachParent_PeekData_PokeData_SignalSuppression) {
   // Yama prevents attaching to a parent. Skip the test if the scope is anything
   // except disabled.
-  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope()) > 0);
+  const int yama_scope = ASSERT_NO_ERRNO_AND_VALUE(YamaPtraceScope());
+  SKIP_IF(yama_scope > 1);
+  if (yama_scope == 1) {
+    // Allow child to trace us.
+    ASSERT_THAT(prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY), SyscallSucceeds());
+  }
 
   // Test PTRACE_POKE/PEEKDATA on both anonymous and file mappings.
   const auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
@@ -1238,6 +2285,46 @@ TEST(PtraceTest, SeizeSetOptions) {
       << " status " << status;
 }
 
+TEST(PtraceTest, SetYAMAPtraceScope) {
+  SKIP_IF(IsRunningWithVFS1());
+
+  // Do not modify the ptrace scope on the host.
+  SKIP_IF(!IsRunningOnGvisor());
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
+
+  const FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(
+      Open(std::string(kYamaPtraceScopePath), O_RDWR));
+
+  ASSERT_THAT(write(fd.get(), "0", 1), SyscallSucceedsWithValue(1));
+
+  ASSERT_THAT(lseek(fd.get(), 0, SEEK_SET), SyscallSucceeds());
+  std::vector<char> buf(10);
+  EXPECT_THAT(read(fd.get(), buf.data(), buf.size()), SyscallSucceeds());
+  EXPECT_STREQ(buf.data(), "0\n");
+
+  // Test that a child can attach to its parent when ptrace_scope is 0.
+  ASSERT_NO_ERRNO(SetCapability(CAP_SYS_PTRACE, false));
+  pid_t const child_pid = fork();
+  if (child_pid == 0) {
+    TEST_PCHECK(CheckPtraceAttach(getppid()) == 0);
+    _exit(0);
+  }
+  ASSERT_THAT(child_pid, SyscallSucceeds());
+
+  int status;
+  ASSERT_THAT(waitpid(child_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+      << " status " << status;
+
+  // Set ptrace_scope back to 1 (and try writing with a newline).
+  ASSERT_THAT(lseek(fd.get(), 0, SEEK_SET), SyscallSucceeds());
+  ASSERT_THAT(write(fd.get(), "1\n", 2), SyscallSucceedsWithValue(2));
+
+  ASSERT_THAT(lseek(fd.get(), 0, SEEK_SET), SyscallSucceeds());
+  EXPECT_THAT(read(fd.get(), buf.data(), buf.size()), SyscallSucceeds());
+  EXPECT_STREQ(buf.data(), "1\n");
+}
+
 }  // namespace
 
 }  // namespace testing
@@ -1250,5 +2337,63 @@ int main(int argc, char** argv) {
     gvisor::testing::RunExecveChild();
   }
 
+  int fd = absl::GetFlag(FLAGS_ptrace_test_fd);
+
+  if (absl::GetFlag(FLAGS_ptrace_test_trace_descendants_allowed)) {
+    gvisor::testing::RunTraceDescendantsAllowed(fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_prctl_set_ptracer_pid)) {
+    gvisor::testing::RunPrctlSetPtracerPID(fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_prctl_set_ptracer_any)) {
+    gvisor::testing::RunPrctlSetPtracerAny(fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_prctl_clear_ptracer)) {
+    gvisor::testing::RunPrctlClearPtracer(fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_prctl_replace_ptracer)) {
+    gvisor::testing::RunPrctlReplacePtracer(
+        absl::GetFlag(FLAGS_ptrace_test_prctl_replace_ptracer_tid), fd);
+  }
+
+  if (absl::GetFlag(
+          FLAGS_ptrace_test_prctl_set_ptracer_and_exit_tracee_thread)) {
+    gvisor::testing::RunPrctlSetPtracerPersistsPastTraceeThreadExit(fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_prctl_set_ptracer_and_exec_non_leader)) {
+    gvisor::testing::RunPrctlSetPtracerDoesNotPersistPastNonLeaderExec(
+        fd);
+  }
+
+  if (absl::GetFlag(
+          FLAGS_ptrace_test_prctl_set_ptracer_and_exit_tracer_thread)) {
+    gvisor::testing::RunPrctlSetPtracerDoesNotPersistPastTracerThreadExit(
+        absl::GetFlag(
+            FLAGS_ptrace_test_prctl_set_ptracer_and_exit_tracer_thread_tid),
+        fd);
+  }
+
+  if (absl::GetFlag(
+          FLAGS_ptrace_test_prctl_set_ptracer_respects_tracer_thread_id)) {
+    gvisor::testing::RunPrctlSetPtracerRespectsTracerThreadID(
+        absl::GetFlag(
+            FLAGS_ptrace_test_prctl_set_ptracer_respects_tracer_thread_id_tid),
+        fd);
+  }
+
+  if (absl::GetFlag(FLAGS_ptrace_test_tracee)) {
+    gvisor::testing::RunTracee(fd);
+  }
+
+  int pid = absl::GetFlag(FLAGS_ptrace_test_trace_tid);
+  if (pid != -1) {
+    gvisor::testing::RunTraceTID(pid, fd);
+  }
+
   return gvisor::testing::RunAllTests();
 }