[libFuzzer] Fix stack overflow detection

Address sanitizer can detect stack exhaustion via its SEGV handler, which is
executed on a separate stack using the sigaltstack mechanism. When libFuzzer is
used with address sanitizer, it installs its own signal handlers which defer to
those put in place by the sanitizer before performing additional actions. In the
particular case of a stack overflow, the current setup fails because libFuzzer
doesn't preserve the flag for executing the signal handler on a separate stack:
when we run out of stack space, the operating system can't run the SEGV handler,
so address sanitizer never reports the issue. See the included test for an
example.

This commit fixes the issue by making libFuzzer preserve the SA_ONSTACK flag
when installing its signal handlers; the dedicated signal-handler stack set up
by the sanitizer runtime appears to be large enough to support the additional
frames from the fuzzer.

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D101824

1 files changed, 26 insertions, 0 deletions

diff --git a/compiler-rt/test/fuzzer/StackOverflowTest.cpp b/compiler-rt/test/fuzzer/StackOverflowTest.cpp
new file mode 100644
index 0000000..c8d8984
--- /dev/null
+++ b/compiler-rt/test/fuzzer/StackOverflowTest.cpp
@@ -0,0 +1,26 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// Stack overflow test for a fuzzer. The fuzzer must find the string "Hi" and
+// cause a stack overflow.
+#include <cstddef>
+#include <cstdint>
+
+volatile int x;
+volatile int y = 1;
+
+int infinite_recursion(char *p) {
+  char *buf = nullptr;
+
+  if (y)
+    infinite_recursion(buf);
+
+  x = 1;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  if (Size >= 2 && Data[0] == 'H' && Data[1] == 'i')
+    infinite_recursion(nullptr);
+  return 0;
+}