Add BPFAction type with Stringer

PiperOrigin-RevId: 226018694
Change-Id: I98965e26fe565f37e98e5df5f997363ab273c91b

3 files changed, 36 insertions, 51 deletions

diff --git a/pkg/sentry/kernel/seccomp.go b/pkg/sentry/kernel/seccomp.go
index d6dc45bbd..cec179246 100644
--- a/pkg/sentry/kernel/seccomp.go
+++ b/pkg/sentry/kernel/seccomp.go
@@ -27,24 +27,6 @@ import (
 
 const maxSyscallFilterInstructions = 1 << 15
 
-type seccompResult int
-
-const (
-	// seccompResultDeny indicates that a syscall should not be executed.
-	seccompResultDeny seccompResult = iota
-
-	// seccompResultAllow indicates that a syscall should be executed.
-	seccompResultAllow
-
-	// seccompResultKill indicates that the task should be killed immediately,
-	// with the exit status indicating that the task was killed by SIGSYS.
-	seccompResultKill
-
-	// seccompResultTrace indicates that a ptracer was successfully notified as
-	// a result of a SECCOMP_RET_TRACE.
-	seccompResultTrace
-)
-
 // seccompData is equivalent to struct seccomp_data, which contains the data
 // passed to seccomp-bpf filters.
 type seccompData struct {
@@ -83,48 +65,47 @@ func seccompSiginfo(t *Task, errno, sysno int32, ip usermem.Addr) *arch.SignalIn
 // in because vsyscalls do not use the values in t.Arch().)
 //
 // Preconditions: The caller must be running on the task goroutine.
-func (t *Task) checkSeccompSyscall(sysno int32, args arch.SyscallArguments, ip usermem.Addr) seccompResult {
-	result := t.evaluateSyscallFilters(sysno, args, ip)
-	switch result & linux.SECCOMP_RET_ACTION {
+func (t *Task) checkSeccompSyscall(sysno int32, args arch.SyscallArguments, ip usermem.Addr) linux.BPFAction {
+	result := linux.BPFAction(t.evaluateSyscallFilters(sysno, args, ip))
+	action := result & linux.SECCOMP_RET_ACTION
+	switch action {
 	case linux.SECCOMP_RET_TRAP:
 		// "Results in the kernel sending a SIGSYS signal to the triggering
 		// task without executing the system call. ... The SECCOMP_RET_DATA
 		// portion of the return value will be passed as si_errno." -
 		// Documentation/prctl/seccomp_filter.txt
-		t.SendSignal(seccompSiginfo(t, int32(result&linux.SECCOMP_RET_DATA), sysno, ip))
-		return seccompResultDeny
+		t.SendSignal(seccompSiginfo(t, int32(result.Data()), sysno, ip))
 
 	case linux.SECCOMP_RET_ERRNO:
 		// "Results in the lower 16-bits of the return value being passed to
 		// userland as the errno without executing the system call."
-		t.Arch().SetReturn(-uintptr(result & linux.SECCOMP_RET_DATA))
-		return seccompResultDeny
+		t.Arch().SetReturn(-uintptr(result.Data()))
 
 	case linux.SECCOMP_RET_TRACE:
 		// "When returned, this value will cause the kernel to attempt to
 		// notify a ptrace()-based tracer prior to executing the system call.
 		// If there is no tracer present, -ENOSYS is returned to userland and
 		// the system call is not executed."
-		if t.ptraceSeccomp(uint16(result & linux.SECCOMP_RET_DATA)) {
-			return seccompResultTrace
+		if !t.ptraceSeccomp(result.Data()) {
+			// This useless-looking temporary is needed because Go.
+			tmp := uintptr(syscall.ENOSYS)
+			t.Arch().SetReturn(-tmp)
+			return linux.SECCOMP_RET_ERRNO
 		}
-		// This useless-looking temporary is needed because Go.
-		tmp := uintptr(syscall.ENOSYS)
-		t.Arch().SetReturn(-tmp)
-		return seccompResultDeny
 
 	case linux.SECCOMP_RET_ALLOW:
 		// "Results in the system call being executed."
-		return seccompResultAllow
 
 	case linux.SECCOMP_RET_KILL_THREAD:
 		// "Results in the task exiting immediately without executing the
 		// system call. The exit status of the task will be SIGSYS, not
 		// SIGKILL."
-		fallthrough
-	default: // consistent with Linux
-		return seccompResultKill
+
+	default:
+		// consistent with Linux
+		return linux.SECCOMP_RET_KILL_THREAD
 	}
+	return action
 }
 
 func (t *Task) evaluateSyscallFilters(sysno int32, args arch.SyscallArguments, ip usermem.Addr) uint32 {
@@ -155,7 +136,7 @@ func (t *Task) evaluateSyscallFilters(sysno int32, args arch.SyscallArguments, i
 		thisRet, err := bpf.Exec(f.([]bpf.Program)[i], input)
 		if err != nil {
 			t.Debugf("seccomp-bpf filter %d returned error: %v", i, err)
-			thisRet = linux.SECCOMP_RET_KILL_THREAD
+			thisRet = uint32(linux.SECCOMP_RET_KILL_THREAD)
 		}
 		// "If multiple filters exist, the return value for the evaluation of a
 		// given system call will always use the highest precedent value." -
diff --git a/pkg/sentry/kernel/task_syscall.go b/pkg/sentry/kernel/task_syscall.go
index 2a39ebc68..9e43f089a 100644
--- a/pkg/sentry/kernel/task_syscall.go
+++ b/pkg/sentry/kernel/task_syscall.go
@@ -199,16 +199,16 @@ func (t *Task) doSyscall() taskRunState {
 	// is rare), not needed for correctness.
 	if t.syscallFilters.Load() != nil {
 		switch r := t.checkSeccompSyscall(int32(sysno), args, usermem.Addr(t.Arch().IP())); r {
-		case seccompResultDeny:
+		case linux.SECCOMP_RET_ERRNO, linux.SECCOMP_RET_TRAP:
 			t.Debugf("Syscall %d: denied by seccomp", sysno)
 			return (*runSyscallExit)(nil)
-		case seccompResultAllow:
+		case linux.SECCOMP_RET_ALLOW:
 			// ok
-		case seccompResultKill:
+		case linux.SECCOMP_RET_KILL_THREAD:
 			t.Debugf("Syscall %d: killed by seccomp", sysno)
 			t.PrepareExit(ExitStatus{Signo: int(linux.SIGSYS)})
 			return (*runExit)(nil)
-		case seccompResultTrace:
+		case linux.SECCOMP_RET_TRACE:
 			t.Debugf("Syscall %d: stopping for PTRACE_EVENT_SECCOMP", sysno)
 			return (*runSyscallAfterPtraceEventSeccomp)(nil)
 		default:
@@ -345,14 +345,18 @@ func (t *Task) doVsyscall(addr usermem.Addr, sysno uintptr) taskRunState {
 	args := t.Arch().SyscallArgs()
 	if t.syscallFilters.Load() != nil {
 		switch r := t.checkSeccompSyscall(int32(sysno), args, addr); r {
-		case seccompResultDeny:
+		case linux.SECCOMP_RET_ERRNO, linux.SECCOMP_RET_TRAP:
 			t.Debugf("vsyscall %d, caller %x: denied by seccomp", sysno, t.Arch().Value(caller))
 			return (*runApp)(nil)
-		case seccompResultAllow:
+		case linux.SECCOMP_RET_ALLOW:
 			// ok
-		case seccompResultTrace:
+		case linux.SECCOMP_RET_TRACE:
 			t.Debugf("vsyscall %d, caller %x: stopping for PTRACE_EVENT_SECCOMP", sysno, t.Arch().Value(caller))
 			return &runVsyscallAfterPtraceEventSeccomp{addr, sysno, caller}
+		case linux.SECCOMP_RET_KILL_THREAD:
+			t.Debugf("vsyscall %d: killed by seccomp", sysno)
+			t.PrepareExit(ExitStatus{Signo: int(linux.SIGSYS)})
+			return (*runExit)(nil)
 		default:
 			panic(fmt.Sprintf("Unknown seccomp result %d", r))
 		}
diff --git a/pkg/sentry/platform/ptrace/subprocess_linux.go b/pkg/sentry/platform/ptrace/subprocess_linux.go
index 25b8e8cb7..e2aab8135 100644
--- a/pkg/sentry/platform/ptrace/subprocess_linux.go
+++ b/pkg/sentry/platform/ptrace/subprocess_linux.go
@@ -38,7 +38,7 @@ const syscallEvent syscall.Signal = 0x80
 // Precondition: the runtime OS thread must be locked.
 func probeSeccomp() bool {
 	// Create a completely new, destroyable process.
-	t, err := attachedThread(0, uint32(linux.SECCOMP_RET_ERRNO))
+	t, err := attachedThread(0, linux.SECCOMP_RET_ERRNO)
 	if err != nil {
 		panic(fmt.Sprintf("seccomp probe failed: %v", err))
 	}
@@ -112,14 +112,14 @@ func createStub() (*thread, error) {
 	// ptrace emulation check. This simplifies using SYSEMU, since seccomp
 	// will never run for emulation. Seccomp will only run for injected
 	// system calls, and thus we can use RET_KILL as our violation action.
-	var defaultAction uint32
+	var defaultAction linux.BPFAction
 	if probeSeccomp() {
 		log.Infof("Latest seccomp behavior found (kernel >= 4.8 likely)")
-		defaultAction = uint32(linux.SECCOMP_RET_KILL_THREAD)
+		defaultAction = linux.SECCOMP_RET_KILL_THREAD
 	} else {
 		// We must rely on SYSEMU behavior; tracing with SYSEMU is broken.
 		log.Infof("Legacy seccomp behavior found (kernel < 4.8 likely)")
-		defaultAction = uint32(linux.SECCOMP_RET_ALLOW)
+		defaultAction = linux.SECCOMP_RET_ALLOW
 	}
 
 	// When creating the new child process, we specify SIGKILL as the
@@ -135,7 +135,7 @@ func createStub() (*thread, error) {
 // attachedThread returns a new attached thread.
 //
 // Precondition: the runtime OS thread must be locked.
-func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
+func attachedThread(flags uintptr, defaultAction linux.BPFAction) (*thread, error) {
 	// Create a BPF program that allows only the system calls needed by the
 	// stub and all its children. This is used to create child stubs
 	// (below), so we must include the ability to fork, but otherwise lock
@@ -148,11 +148,11 @@ func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
 				syscall.SYS_TIME:         {},
 				309:                      {}, // SYS_GETCPU.
 			},
-			Action:   uint32(linux.SECCOMP_RET_TRAP),
+			Action:   linux.SECCOMP_RET_TRAP,
 			Vsyscall: true,
 		},
 	}
-	if defaultAction != uint32(linux.SECCOMP_RET_ALLOW) {
+	if defaultAction != linux.SECCOMP_RET_ALLOW {
 		rules = append(rules, seccomp.RuleSet{
 			Rules: seccomp.SyscallRules{
 				syscall.SYS_CLONE: []seccomp.Rule{
@@ -191,7 +191,7 @@ func attachedThread(flags uintptr, defaultAction uint32) (*thread, error) {
 				syscall.SYS_MMAP:   {},
 				syscall.SYS_MUNMAP: {},
 			},
-			Action: uint32(linux.SECCOMP_RET_ALLOW),
+			Action: linux.SECCOMP_RET_ALLOW,
 		})
 	}
 	instrs, err := seccomp.BuildProgram(rules, defaultAction)