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usertrap: disable syscall patching when ptraced #12325

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Merged
copybara-service merged 2 commits into from
Dec 8, 2025
Merged

usertrap: disable syscall patching when ptraced #12325

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62cb91e
usertrap: disable syscall patching when ptraced
ret2libc Nov 21, 2025
3c52fed
Add warning if syscall patches exist already for a ptraced process
ret2libc Dec 3, 2025
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16 changes: 16 additions & 0 deletions pkg/sentry/platform/systrap/usertrap/usertrap_amd64.go
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Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,22 @@ func (s *State) PatchSyscall(ctx context.Context, ac *arch.Context64, mm memoryM
return fmt.Errorf("no task found")
}

// Skip syscall patching when the task is being ptraced, because
// single-stepping and other debugger features are incompatible with
// the "syshandler" routine used to handle patched syscalls (see
// syshandler_amd64.S). This incompatibility can result in inconsistent
// process states and failures (e.g. SIGSEGV).
// TODO(gvisor.dev/issue/11649): for a full fix we'd need to roll back
// existing patched syscalls, in case the traced program was patched
// before being traced (e.g. PTRACE_ATTACH on an already running
// process).
if task.Tracer() != nil {
if s.nextTrap > 0 {
ctx.Warningf("LIKELY ERROR: Attached tracer to process with patched syscalls (traps %d)! Systrap is not fully compatible with ptrace/debuggers, program may die unexpectedly soon!", s.nextTrap)
}
return nil
}

s.mu.Lock()
defer s.mu.Unlock()

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