Merge release-20200818.0-54-gcb573c8e0 (automated)

13 files changed, 513 insertions, 8 deletions

diff --git a/pkg/sentry/fsimpl/host/connected_endpoint_refs.go b/pkg/sentry/fsimpl/host/connected_endpoint_refs.go
index 1f13a2608..3b7bf599e 100644
--- a/pkg/sentry/fsimpl/host/connected_endpoint_refs.go
+++ b/pkg/sentry/fsimpl/host/connected_endpoint_refs.go
@@ -1,11 +1,11 @@
 package host
 
 import (
+	"runtime"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
 	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
-	"runtime"
 )
 
 // ownerType is used to customize logging. Note that we use a pointer to T so
diff --git a/pkg/sentry/fsimpl/host/inode_refs.go b/pkg/sentry/fsimpl/host/inode_refs.go
index 2c67758a0..55c0fb3a9 100644
--- a/pkg/sentry/fsimpl/host/inode_refs.go
+++ b/pkg/sentry/fsimpl/host/inode_refs.go
@@ -1,11 +1,11 @@
 package host
 
 import (
+	"runtime"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
 	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
-	"runtime"
 )
 
 // ownerType is used to customize logging. Note that we use a pointer to T so
diff --git a/pkg/sentry/fsimpl/sys/kcov.go b/pkg/sentry/fsimpl/sys/kcov.go
new file mode 100644
index 000000000..92710d877
--- /dev/null
+++ b/pkg/sentry/fsimpl/sys/kcov.go
@@ -0,0 +1,116 @@
+// Copyright 2020 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 sys
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+func (fs *filesystem) newKcovFile(ctx context.Context, creds *auth.Credentials) *kernfs.Dentry {
+	k := &kcovInode{}
+	k.InodeAttrs.Init(creds, 0, 0, fs.NextIno(), linux.S_IFREG|0600)
+	d := &kernfs.Dentry{}
+	d.Init(k)
+	return d
+}
+
+// kcovInode implements kernfs.Inode.
+type kcovInode struct {
+	kernfs.InodeAttrs
+	kernfs.InodeNoopRefCount
+	kernfs.InodeNotSymlink
+	kernfs.InodeNotDirectory
+}
+
+func (i *kcovInode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	k := kernel.KernelFromContext(ctx)
+	if k == nil {
+		panic("KernelFromContext returned nil")
+	}
+	fd := &kcovFD{
+		inode: i,
+		kcov:  k.NewKcov(),
+	}
+
+	if err := fd.vfsfd.Init(fd, opts.Flags, rp.Mount(), vfsd, &vfs.FileDescriptionOptions{
+		DenyPRead:  true,
+		DenyPWrite: true,
+	}); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+type kcovFD struct {
+	vfs.FileDescriptionDefaultImpl
+	vfs.NoLockFD
+
+	vfsfd vfs.FileDescription
+	inode *kcovInode
+	kcov  *kernel.Kcov
+}
+
+// Ioctl implements vfs.FileDescriptionImpl.Ioctl.
+func (fd *kcovFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
+	cmd := uint32(args[1].Int())
+	arg := args[2].Uint64()
+	switch uint32(cmd) {
+	case linux.KCOV_INIT_TRACE:
+		return 0, fd.kcov.InitTrace(arg)
+	case linux.KCOV_ENABLE:
+		return 0, fd.kcov.EnableTrace(ctx, uint8(arg))
+	case linux.KCOV_DISABLE:
+		if arg != 0 {
+			// This arg is unused; it should be 0.
+			return 0, syserror.EINVAL
+		}
+		return 0, fd.kcov.DisableTrace(ctx)
+	default:
+		return 0, syserror.ENOTTY
+	}
+}
+
+// ConfigureMmap implements vfs.FileDescriptionImpl.ConfigureMmap.
+func (fd *kcovFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	return fd.kcov.ConfigureMMap(ctx, opts)
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *kcovFD) Release(ctx context.Context) {
+	// kcov instances have reference counts in Linux, but this seems sufficient
+	// for our purposes.
+	fd.kcov.Reset()
+}
+
+// SetStat implements vfs.FileDescriptionImpl.SetStat.
+func (fd *kcovFD) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
+	creds := auth.CredentialsFromContext(ctx)
+	fs := fd.vfsfd.VirtualDentry().Mount().Filesystem()
+	return fd.inode.SetStat(ctx, fs, creds, opts)
+}
+
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *kcovFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	return fd.inode.Stat(ctx, fd.vfsfd.Mount().Filesystem(), opts)
+}
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index 393feb802..1f042d9f7 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -21,6 +21,7 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/coverage"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -73,7 +74,7 @@ func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		}),
 		"firmware": fs.newDir(creds, defaultSysDirMode, nil),
 		"fs":       fs.newDir(creds, defaultSysDirMode, nil),
-		"kernel":   fs.newDir(creds, defaultSysDirMode, nil),
+		"kernel":   kernelDir(ctx, fs, creds),
 		"module":   fs.newDir(creds, defaultSysDirMode, nil),
 		"power":    fs.newDir(creds, defaultSysDirMode, nil),
 	})
@@ -94,6 +95,21 @@ func cpuDir(ctx context.Context, fs *filesystem, creds *auth.Credentials) *kernf
 	return fs.newDir(creds, defaultSysDirMode, children)
 }
 
+func kernelDir(ctx context.Context, fs *filesystem, creds *auth.Credentials) *kernfs.Dentry {
+	// If kcov is available, set up /sys/kernel/debug/kcov. Technically, debugfs
+	// should be mounted at debug/, but for our purposes, it is sufficient to
+	// keep it in sys.
+	var children map[string]*kernfs.Dentry
+	if coverage.KcovAvailable() {
+		children = map[string]*kernfs.Dentry{
+			"debug": fs.newDir(creds, linux.FileMode(0700), map[string]*kernfs.Dentry{
+				"kcov": fs.newKcovFile(ctx, creds),
+			}),
+		}
+	}
+	return fs.newDir(creds, defaultSysDirMode, children)
+}
+
 // Release implements vfs.FilesystemImpl.Release.
 func (fs *filesystem) Release(ctx context.Context) {
 	fs.Filesystem.VFSFilesystem().VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
diff --git a/pkg/sentry/fsimpl/tmpfs/inode_refs.go b/pkg/sentry/fsimpl/tmpfs/inode_refs.go
index 3245ede1f..8b7ff185f 100644
--- a/pkg/sentry/fsimpl/tmpfs/inode_refs.go
+++ b/pkg/sentry/fsimpl/tmpfs/inode_refs.go
@@ -1,11 +1,11 @@
 package tmpfs
 
 import (
+	"runtime"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
 	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
-	"runtime"
 )
 
 // ownerType is used to customize logging. Note that we use a pointer to T so
diff --git a/pkg/sentry/kernel/kcov.go b/pkg/sentry/kernel/kcov.go
new file mode 100644
index 000000000..aad63aa99
--- /dev/null
+++ b/pkg/sentry/kernel/kcov.go
@@ -0,0 +1,321 @@
+// Copyright 2020 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 kernel
+
+import (
+	"fmt"
+	"io"
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/coverage"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/mm"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/usage"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// kcovAreaSizeMax is the maximum number of uint64 entries allowed in the kcov
+// area. On Linux, the maximum is INT_MAX / 8.
+const kcovAreaSizeMax = 10 * 1024 * 1024
+
+// Kcov provides kernel coverage data to userspace through a memory-mapped
+// region, as kcov does in Linux.
+//
+// To give the illusion that the data is always up to date, we update the shared
+// memory every time before we return to userspace.
+type Kcov struct {
+	// mfp provides application memory. It is immutable after creation.
+	mfp pgalloc.MemoryFileProvider
+
+	// mu protects all of the fields below.
+	mu sync.RWMutex
+
+	// mode is the current kcov mode.
+	mode uint8
+
+	// size is the size of the mapping through which the kernel conveys coverage
+	// information to userspace.
+	size uint64
+
+	// owningTask is the task that currently owns coverage data on the system. The
+	// interface for kcov essentially requires that coverage is only going to a
+	// single task. Note that kcov should only generate coverage data for the
+	// owning task, but we currently generate global coverage.
+	owningTask *Task
+
+	// count is a locally cached version of the first uint64 in the kcov data,
+	// which is the number of subsequent entries representing PCs.
+	//
+	// It is used with kcovInode.countBlock(), to copy in/out the first element of
+	// the actual data in an efficient manner, avoid boilerplate, and prevent
+	// accidental garbage escapes by the temporary counts.
+	count uint64
+
+	mappable *mm.SpecialMappable
+}
+
+// NewKcov creates and returns a Kcov instance.
+func (k *Kernel) NewKcov() *Kcov {
+	return &Kcov{
+		mfp: k,
+	}
+}
+
+var coveragePool = sync.Pool{
+	New: func() interface{} {
+		return make([]byte, 0)
+	},
+}
+
+// TaskWork implements TaskWorker.TaskWork.
+func (kcov *Kcov) TaskWork(t *Task) {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	rw := &kcovReadWriter{
+		mf: kcov.mfp.MemoryFile(),
+		fr: kcov.mappable.FileRange(),
+	}
+
+	// Read in the PC count.
+	if _, err := safemem.ReadFullToBlocks(rw, kcov.countBlock()); err != nil {
+		panic(fmt.Sprintf("Internal error reading count from kcov area: %v", err))
+	}
+
+	rw.off = 8 * (1 + kcov.count)
+	n := coverage.ConsumeCoverageData(&kcovIOWriter{rw})
+
+	// Update the pc count, based on the number of entries written. Note that if
+	// we reached the end of the kcov area, we may not have written everything in
+	// output.
+	kcov.count += uint64(n / 8)
+	rw.off = 0
+	if _, err := safemem.WriteFullFromBlocks(rw, kcov.countBlock()); err != nil {
+		panic(fmt.Sprintf("Internal error writing count to kcov area: %v", err))
+	}
+
+	// Re-register for future work.
+	t.RegisterWork(kcov)
+}
+
+// InitTrace performs the KCOV_INIT_TRACE ioctl.
+func (kcov *Kcov) InitTrace(size uint64) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	if kcov.mode != linux.KCOV_MODE_DISABLED {
+		return syserror.EBUSY
+	}
+
+	// To simplify all the logic around mapping, we require that the length of the
+	// shared region is a multiple of the system page size.
+	if (8*size)&(usermem.PageSize-1) != 0 {
+		return syserror.EINVAL
+	}
+
+	// We need space for at least two uint64s to hold current position and a
+	// single PC.
+	if size < 2 || size > kcovAreaSizeMax {
+		return syserror.EINVAL
+	}
+
+	kcov.size = size
+	kcov.mode = linux.KCOV_MODE_INIT
+	return nil
+}
+
+// EnableTrace performs the KCOV_ENABLE_TRACE ioctl.
+func (kcov *Kcov) EnableTrace(ctx context.Context, traceMode uint8) error {
+	t := TaskFromContext(ctx)
+	if t == nil {
+		panic("kcovInode.EnableTrace() cannot be used outside of a task goroutine")
+	}
+
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	// KCOV_ENABLE must be preceded by KCOV_INIT_TRACE and an mmap call.
+	if kcov.mode != linux.KCOV_MODE_INIT || kcov.mappable == nil {
+		return syserror.EINVAL
+	}
+
+	switch traceMode {
+	case linux.KCOV_TRACE_PC:
+		kcov.mode = traceMode
+	case linux.KCOV_TRACE_CMP:
+		// We do not support KCOV_MODE_TRACE_CMP.
+		return syserror.ENOTSUP
+	default:
+		return syserror.EINVAL
+	}
+
+	if kcov.owningTask != nil && kcov.owningTask != t {
+		return syserror.EBUSY
+	}
+
+	kcov.owningTask = t
+	t.RegisterWork(kcov)
+
+	// Clear existing coverage data; the task expects to read only coverage data
+	// from the time it is activated.
+	coverage.ClearCoverageData()
+	return nil
+}
+
+// DisableTrace performs the KCOV_DISABLE_TRACE ioctl.
+func (kcov *Kcov) DisableTrace(ctx context.Context) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	t := TaskFromContext(ctx)
+	if t == nil {
+		panic("kcovInode.EnableTrace() cannot be used outside of a task goroutine")
+	}
+
+	if t != kcov.owningTask {
+		return syserror.EINVAL
+	}
+	kcov.owningTask = nil
+	kcov.mode = linux.KCOV_MODE_INIT
+	kcov.resetLocked()
+	return nil
+}
+
+// Reset is called when the owning task exits.
+func (kcov *Kcov) Reset() {
+	kcov.mu.Lock()
+	kcov.resetLocked()
+	kcov.mu.Unlock()
+}
+
+// The kcov instance is reset when the owning task exits or when tracing is
+// disabled.
+func (kcov *Kcov) resetLocked() {
+	kcov.owningTask = nil
+	if kcov.mappable != nil {
+		kcov.mappable = nil
+	}
+}
+
+// ConfigureMMap is called by the vfs.FileDescription for this kcov instance to
+// implement vfs.FileDescription.ConfigureMMap.
+func (kcov *Kcov) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	kcov.mu.Lock()
+	defer kcov.mu.Unlock()
+
+	if kcov.mode != linux.KCOV_MODE_INIT {
+		return syserror.EINVAL
+	}
+
+	if kcov.mappable == nil {
+		// Set up the kcov area.
+		fr, err := kcov.mfp.MemoryFile().Allocate(kcov.size*8, usage.Anonymous)
+		if err != nil {
+			return err
+		}
+
+		// Get the thread id for the mmap name.
+		t := TaskFromContext(ctx)
+		if t == nil {
+			panic("ThreadFromContext returned nil")
+		}
+		// For convenience, a special mappable is used here. Note that these mappings
+		// will look different under /proc/[pid]/maps than they do on Linux.
+		kcov.mappable = mm.NewSpecialMappable(fmt.Sprintf("[kcov:%d]", t.ThreadID()), kcov.mfp, fr)
+	}
+	opts.Mappable = kcov.mappable
+	opts.MappingIdentity = kcov.mappable
+	return nil
+}
+
+// kcovReadWriter implements safemem.Reader and safemem.Writer.
+type kcovReadWriter struct {
+	off uint64
+	mf  *pgalloc.MemoryFile
+	fr  memmap.FileRange
+}
+
+// ReadToBlocks implements safemem.Reader.ReadToBlocks.
+func (rw *kcovReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	if dsts.IsEmpty() {
+		return 0, nil
+	}
+
+	// Limit the read to the kcov range and check for overflow.
+	if rw.fr.Length() <= rw.off {
+		return 0, io.EOF
+	}
+	start := rw.fr.Start + rw.off
+	end := rw.fr.Start + rw.fr.Length()
+	if rend := start + dsts.NumBytes(); rend < end {
+		end = rend
+	}
+
+	// Get internal mappings.
+	bs, err := rw.mf.MapInternal(memmap.FileRange{start, end}, usermem.Read)
+	if err != nil {
+		return 0, err
+	}
+
+	// Copy from internal mappings.
+	n, err := safemem.CopySeq(dsts, bs)
+	rw.off += n
+	return n, err
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+func (rw *kcovReadWriter) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	if srcs.IsEmpty() {
+		return 0, nil
+	}
+
+	// Limit the write to the kcov area and check for overflow.
+	if rw.fr.Length() <= rw.off {
+		return 0, io.EOF
+	}
+	start := rw.fr.Start + rw.off
+	end := rw.fr.Start + rw.fr.Length()
+	if wend := start + srcs.NumBytes(); wend < end {
+		end = wend
+	}
+
+	// Get internal mapping.
+	bs, err := rw.mf.MapInternal(memmap.FileRange{start, end}, usermem.Write)
+	if err != nil {
+		return 0, err
+	}
+
+	// Copy to internal mapping.
+	n, err := safemem.CopySeq(bs, srcs)
+	rw.off += n
+	return n, err
+}
+
+// kcovIOWriter implements io.Writer as a basic wrapper over kcovReadWriter.
+type kcovIOWriter struct {
+	rw *kcovReadWriter
+}
+
+// Write implements io.Writer.Write.
+func (w *kcovIOWriter) Write(p []byte) (int, error) {
+	bs := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(p))
+	n, err := safemem.WriteFullFromBlocks(w.rw, bs)
+	return int(n), err
+}
diff --git a/pkg/sentry/kernel/kcov_unsafe.go b/pkg/sentry/kernel/kcov_unsafe.go
new file mode 100644
index 000000000..6f64022eb
--- /dev/null
+++ b/pkg/sentry/kernel/kcov_unsafe.go
@@ -0,0 +1,28 @@
+// Copyright 2020 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 kernel
+
+import (
+	"unsafe"
+
+	"gvisor.dev/gvisor/pkg/safemem"
+)
+
+// countBlock provides a safemem.BlockSeq for k.count.
+//
+// Like k.count, the block returned is protected by k.mu.
+func (k *Kcov) countBlock() safemem.BlockSeq {
+	return safemem.BlockSeqOf(safemem.BlockFromSafePointer(unsafe.Pointer(&k.count), int(unsafe.Sizeof(k.count))))
+}
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 2e0175e36..402aa1718 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -248,7 +248,7 @@ type Kernel struct {
 	// SpecialOpts contains special kernel options.
 	SpecialOpts
 
-	// VFS keeps the filesystem state used across the kernel.
+	// vfs keeps the filesystem state used across the kernel.
 	vfs vfs.VirtualFilesystem
 
 	// hostMount is the Mount used for file descriptors that were imported
diff --git a/pkg/sentry/kernel/kernel_state_autogen.go b/pkg/sentry/kernel/kernel_state_autogen.go
index 106e237ec..e514b07d6 100644
--- a/pkg/sentry/kernel/kernel_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_state_autogen.go
@@ -1061,6 +1061,7 @@ func (x *Task) StateFields() []string {
 		"rseqSignature",
 		"robustList",
 		"startTime",
+		"kcov",
 	}
 }
 
@@ -1134,6 +1135,7 @@ func (x *Task) StateSave(m state.Sink) {
 	m.Save(58, &x.rseqSignature)
 	m.Save(59, &x.robustList)
 	m.Save(60, &x.startTime)
+	m.Save(61, &x.kcov)
 }
 
 func (x *Task) StateLoad(m state.Source) {
@@ -1196,6 +1198,7 @@ func (x *Task) StateLoad(m state.Source) {
 	m.Load(58, &x.rseqSignature)
 	m.Load(59, &x.robustList)
 	m.Load(60, &x.startTime)
+	m.Load(61, &x.kcov)
 	m.LoadValue(31, new(*Task), func(y interface{}) { x.loadPtraceTracer(y.(*Task)) })
 	m.LoadValue(47, new([]bpf.Program), func(y interface{}) { x.loadSyscallFilters(y.([]bpf.Program)) })
 	m.AfterLoad(x.afterLoad)
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index 5aee699e7..a436610c9 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -574,6 +574,11 @@ type Task struct {
 	//
 	// startTime is protected by mu.
 	startTime ktime.Time
+
+	// kcov is the kcov instance providing code coverage owned by this task.
+	//
+	// kcov is exclusive to the task goroutine.
+	kcov *Kcov
 }
 
 func (t *Task) savePtraceTracer() *Task {
@@ -903,3 +908,16 @@ func (t *Task) UID() uint32 {
 func (t *Task) GID() uint32 {
 	return uint32(t.Credentials().EffectiveKGID)
 }
+
+// SetKcov sets the kcov instance associated with t.
+func (t *Task) SetKcov(k *Kcov) {
+	t.kcov = k
+}
+
+// ResetKcov clears the kcov instance associated with t.
+func (t *Task) ResetKcov() {
+	if t.kcov != nil {
+		t.kcov.Reset()
+		t.kcov = nil
+	}
+}
diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index c165d6cb1..b76f7f503 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -239,6 +239,8 @@ func (*runExitMain) execute(t *Task) taskRunState {
 	t.traceExitEvent()
 	lastExiter := t.exitThreadGroup()
 
+	t.ResetKcov()
+
 	// If the task has a cleartid, and the thread group wasn't killed by a
 	// signal, handle that before releasing the MM.
 	if t.cleartid != 0 {
diff --git a/pkg/sentry/platform/ring0/defs_impl_arm64.go b/pkg/sentry/platform/ring0/defs_impl_arm64.go
index 9fb351879..eba2eac30 100644
--- a/pkg/sentry/platform/ring0/defs_impl_arm64.go
+++ b/pkg/sentry/platform/ring0/defs_impl_arm64.go
@@ -1,12 +1,13 @@
 package ring0
 
 import (
-	"fmt"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/platform/ring0/pagetables"
-	"gvisor.dev/gvisor/pkg/usermem"
 	"io"
 	"reflect"
+
+	"fmt"
+	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 // Useful bits.
diff --git a/pkg/sentry/socket/unix/socket_refs.go b/pkg/sentry/socket/unix/socket_refs.go
index 6ed7b1151..4c6ec186b 100644
--- a/pkg/sentry/socket/unix/socket_refs.go
+++ b/pkg/sentry/socket/unix/socket_refs.go
@@ -1,11 +1,11 @@
 package unix
 
 import (
+	"runtime"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
 	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
-	"runtime"
 )
 
 // ownerType is used to customize logging. Note that we use a pointer to T so