Use TRAP to simplify vsyscall emulation.

PiperOrigin-RevId: 218592058
Change-Id: I373a2d813aa6cc362500dd5a894c0b214a1959d7

1 files changed, 12 insertions, 12 deletions

diff --git a/pkg/sentry/platform/ptrace/subprocess.go b/pkg/sentry/platform/ptrace/subprocess.go
index 6a9da5db8..2cd49d1ec 100644
--- a/pkg/sentry/platform/ptrace/subprocess.go
+++ b/pkg/sentry/platform/ptrace/subprocess.go
@@ -357,15 +357,13 @@ func (t *thread) destroy() {
 
 // init initializes trace options.
 func (t *thread) init() {
-	// Set our TRACESYSGOOD option to differeniate real SIGTRAP. Also, we
-	// require the SECCOMP option to ensure that seccomp violations
-	// generate a ptrace event.
+	// Set our TRACESYSGOOD option to differeniate real SIGTRAP.
 	_, _, errno := syscall.RawSyscall6(
 		syscall.SYS_PTRACE,
 		syscall.PTRACE_SETOPTIONS,
 		uintptr(t.tid),
 		0,
-		syscall.PTRACE_O_TRACESYSGOOD|_PTRACE_O_TRACESECCOMP,
+		syscall.PTRACE_O_TRACESYSGOOD,
 		0, 0)
 	if errno != 0 {
 		panic(fmt.Sprintf("ptrace set options failed: %v", errno))
@@ -522,12 +520,6 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 			// Ensure registers are sane.
 			updateSyscallRegs(regs)
 			return true
-		} else if sig == (seccompEvent | syscall.SIGTRAP) {
-			// Seccomp is enabled, and caught the system call. This
-			// is an emulated vsyscall call, since those are caught
-			// only by seccomp and explicitly set to trace.
-			updateSyscallRegs(regs)
-			return true
 		} else if sig == syscall.SIGSTOP {
 			// SIGSTOP was delivered to another thread in the same thread
 			// group, which initiated another group stop. Just ignore it.
@@ -544,9 +536,17 @@ func (s *subprocess) switchToApp(c *context, ac arch.Context) bool {
 		// either delivered from the kernel or from this process. We
 		// don't respect other signals.
 		if c.signalInfo.Code > 0 {
-			return false // kernel.
+			// The signal was generated by the kernel. We inspect
+			// the signal information, and may patch it in order to
+			// faciliate vsyscall emulation. See patchSignalInfo.
+			patchSignalInfo(regs, &c.signalInfo)
+			return false
 		} else if c.signalInfo.Code <= 0 && c.signalInfo.Pid() == int32(os.Getpid()) {
-			return false // this process.
+			// The signal was generated by this process. That means
+			// that it was an interrupt or something else that we
+			// should bail for. Note that we ignore signals
+			// generated by other processes.
+			return false
 		}
 	}
 }