[compiler-rt] [sanitizer] Don't TestPTrace() if SPARC; don't give up if internal_fork() fails (PR #152072)
Thurston Dang via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 5 11:00:45 PDT 2025
https://github.com/thurstond updated https://github.com/llvm/llvm-project/pull/152072
>From 890adf486cd16e531eeb6ac18c2522f2969364d7 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Tue, 5 Aug 2025 03:46:30 +0000
Subject: [PATCH 1/4] [sanitizer] Don't TestPTrace() if SPARC
Fixes corner case of https://github.com/llvm/llvm-project/pull/151406
internal_fork() on SPARC actually calls __fork(). We can't safely fork,
because it's possible seccomp has been configured to disallow fork() but
allow clone().
Also adds some comments/TODOs.
---
.../sanitizer_stoptheworld_linux_libcdep.cpp | 25 ++++++++++++++++---
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
index d5cf0f14dfeb8..00426de50a388 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -409,6 +409,12 @@ struct ScopedSetTracerPID {
// process with a shared virtual address space and shared TLS, and therefore
// cannot use waitpid() due to the shared errno.
static void TestPTrace() {
+# if SANITIZER_SPARC
+ // internal_fork() on SPARC actually calls __fork(). We can't safely fork,
+ // because it's possible seccomp has been configured to disallow fork() but
+ // allow clone().
+ Report("WARNING: skipping TestPTrace() because this is SPARC\n");
+# else
// Heuristic: only check the first time this is called. This is not always
// correct (e.g., user manually triggers leak detection, then updates
// seccomp, then leak detection is triggered again).
@@ -417,26 +423,36 @@ static void TestPTrace() {
return;
checked = true;
- // We hope that fork() is not too expensive, because of copy-on-write.
+ // Hopefully internal_fork() is not too expensive, thanks to copy-on-write.
// Besides, this is only called the first time.
+ // Note that internal_fork() on non-SPARC Linux actually calls
+ // SYSCALL(clone); thus, it is reasonable to use it because if seccomp kills
+ // TestPTrace(), it would have killed StopTheWorld() anyway.
int pid = internal_fork();
if (pid < 0) {
int rverrno;
- if (internal_iserror(pid, &rverrno)) {
+ if (internal_iserror(pid, &rverrno))
Report("WARNING: TestPTrace() failed to fork (errno %d)\n", rverrno);
- }
- internal__exit(-1);
+
+ // We don't abort the sanitizer - it's still worth letting the sanitizer
+ // try.
+ return;
}
if (pid == 0) {
// Child subprocess
+
+ // TODO: consider checking return value of internal_ptrace, to handle
+ // SCMP_ACT_ERRNO. However, be careful not to consume too many
+ // resources performing a proper ptrace.
internal_ptrace(PTRACE_ATTACH, 0, nullptr, nullptr);
internal__exit(0);
} else {
int wstatus;
internal_waitpid(pid, &wstatus, 0);
+ // Handle SCMP_ACT_KILL
if (WIFSIGNALED(wstatus)) {
VReport(0,
"Warning: ptrace appears to be blocked (is seccomp enabled?). "
@@ -446,6 +462,7 @@ static void TestPTrace() {
// try.
}
}
+# endif
}
void StopTheWorld(StopTheWorldCallback callback, void *argument) {
>From 2ec6558aa73c287fe9c21580ac5896646e2766bb Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Tue, 5 Aug 2025 04:23:18 +0000
Subject: [PATCH 2/4] Fix up "process" -> "thread"
---
.../sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
index 00426de50a388..f38e44cdc5960 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -405,8 +405,8 @@ struct ScopedSetTracerPID {
// This detects whether ptrace is blocked (e.g., by seccomp), by forking and
// then attempting ptrace.
-// This separate check is necessary because StopTheWorld() creates a child
-// process with a shared virtual address space and shared TLS, and therefore
+// This separate check is necessary because StopTheWorld() creates a thread
+// with a shared virtual address space and shared TLS, and therefore
// cannot use waitpid() due to the shared errno.
static void TestPTrace() {
# if SANITIZER_SPARC
>From 5a630c5684a14dd768c0456238086914fe33d458 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Tue, 5 Aug 2025 17:54:52 +0000
Subject: [PATCH 3/4] Elaborate on SPARC warning
---
.../sanitizer_stoptheworld_linux_libcdep.cpp | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
index f38e44cdc5960..0d1f21bad0944 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -413,7 +413,12 @@ static void TestPTrace() {
// internal_fork() on SPARC actually calls __fork(). We can't safely fork,
// because it's possible seccomp has been configured to disallow fork() but
// allow clone().
- Report("WARNING: skipping TestPTrace() because this is SPARC\n");
+ Report("Warning: skipping TestPTrace() because this is SPARC\n");
+ Report(
+ "If seccomp blocks ptrace, LeakSanitizer may hang without further "
+ "notice\n");
+ Report(
+ "If seccomp does not block ptrace, you can safely ignore this warning\n");
# else
// Heuristic: only check the first time this is called. This is not always
// correct (e.g., user manually triggers leak detection, then updates
>From 18d07e49aee94888f7578026d1e7993eb9946bf7 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Tue, 5 Aug 2025 18:00:22 +0000
Subject: [PATCH 4/4] CAPITALIZE
---
.../sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
index 0d1f21bad0944..5fde65ea48c42 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -413,7 +413,7 @@ static void TestPTrace() {
// internal_fork() on SPARC actually calls __fork(). We can't safely fork,
// because it's possible seccomp has been configured to disallow fork() but
// allow clone().
- Report("Warning: skipping TestPTrace() because this is SPARC\n");
+ Report("WARNING: skipping TestPTrace() because this is SPARC\n");
Report(
"If seccomp blocks ptrace, LeakSanitizer may hang without further "
"notice\n");
@@ -460,7 +460,7 @@ static void TestPTrace() {
// Handle SCMP_ACT_KILL
if (WIFSIGNALED(wstatus)) {
VReport(0,
- "Warning: ptrace appears to be blocked (is seccomp enabled?). "
+ "WARNING: ptrace appears to be blocked (is seccomp enabled?). "
"LeakSanitizer may hang.\n");
VReport(0, "Child exited with signal %d.\n", WTERMSIG(wstatus));
// We don't abort the sanitizer - it's still worth letting the sanitizer
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