[compiler-rt] [tsan] Lazily call 'personality' to minimize sandbox violations (PR #79334)

[Thurston Dang via llvm-commits]

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@@ -267,6 +267,14 @@ static void ReExecIfNeeded() {
   if (reexec) {
     // Don't check the address space since we're going to re-exec anyway.
   } else if (!CheckAndProtect(false, false, false)) {
+    // ASLR personality check.
+    // N.B. 'personality' is sometimes forbidden by sandboxes, so we only call
+    // this as a last resort (when the memory mapping is incompatible and TSan
+    // would fail anyway).
+    int old_personality = personality(0xffffffff);
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thurstond wrote:

Ah, I see! I've added `compiler-rt/test/sanitizer_common/TestCases/Linux/sandbox_forbidden_functions.cpp`. I tested that the test failed with TSan in the absence of this fix, and passes with this fix.

Note that it does have a false positive when TSan is run with high-entropy ASLR: in that environment, calling 'personality' (to check/disable ASLR) is the intended behavior.

https://github.com/llvm/llvm-project/pull/79334