[sanitizer-common] [Darwin] Provide warnings for common sandbox issues

[ndrewh]

We currently do not handle errors in task_set_exc_guard_behavior. If this fails, mmap can unexpectedly crash.
We also do not currently provide a clear warning if no external symbolizers are found.

rdar://163798535

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Andrew Haberlandt (ndrewh)

Changes

We currently do not handle errors in task_set_exc_guard_behavior. If this fails, mmap can unexpectedly crash.

Here, we add a warning to notify users when this occurs.

---

Full diff: https://github.com/llvm/llvm-project/pull/165907.diff

1 Files Affected:

• (modified) compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp (+12-1)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
index b0a29db908639..a118f7da2c856 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
@@ -960,7 +960,18 @@ static void DisableMmapExcGuardExceptions() {
       RTLD_DEFAULT, "task_set_exc_guard_behavior");
   if (set_behavior == nullptr) return;
   const task_exc_guard_behavior_t task_exc_guard_none = 0;
-  set_behavior(mach_task_self(), task_exc_guard_none);
+  kern_return_t res = set_behavior(mach_task_self(), task_exc_guard_none);
+  if (res != KERN_SUCCESS) {
+    Report(
+        "WARN: AddressSanitizer: task_set_exc_guard_behavior returned %d (%s), "
+        "mmap may fail unexpectedly.\n",
+        res, mach_error_string(res));
+    if (res == KERN_DENIED) {
+      Report(
+          "HINT: Check that task_set_exc_guard_behavior is allowed by "
+          "sandbox.\n");
+    }
+  }
 }
 
 static void VerifyInterceptorsWorking();

[DanBlackwell]

Thanks for this, looks good. Possibly could have been better to split across 2 separate PRs.