Read fault address on arm64 using proposed kernel API.

On aarch64, the top 8 bits of the address (i.e. the tag bits) of
the fault address in si_addr are always clear. This isn't ideal for
MTE which will require these bits in order to correctly diagnose
tag mismatches.

A proposed kernel patch [1] exposes the full fault address including
the tag bits as part of the ucontext. Change debuggerd to read this
fault address if available.

[1] https://patchwork.kernel.org/patch/11435077/

Bug: 135772972
Change-Id: Ia05be574113860f4e9ecc36a310c4b740e0c4afb

1 files changed, 26 insertions, 0 deletions

diff --git a/debuggerd/debuggerd_test.cpp b/debuggerd/debuggerd_test.cpp
index 6a8cc563d..054f83675 100644
--- a/debuggerd/debuggerd_test.cpp
+++ b/debuggerd/debuggerd_test.cpp
@@ -305,6 +305,32 @@ TEST_F(CrasherTest, smoke) {
   ASSERT_MATCH(result, R"(signal 11 \(SIGSEGV\), code 1 \(SEGV_MAPERR\), fault addr 0xdead)");
 }
 
+TEST_F(CrasherTest, tagged_fault_addr) {
+#if !defined(__aarch64__)
+  GTEST_SKIP() << "Requires aarch64";
+#endif
+  int intercept_result;
+  unique_fd output_fd;
+  StartProcess([]() {
+    *reinterpret_cast<volatile char*>(0x100000000000dead) = '1';
+  });
+
+  StartIntercept(&output_fd);
+  FinishCrasher();
+  AssertDeath(SIGSEGV);
+  FinishIntercept(&intercept_result);
+
+  ASSERT_EQ(1, intercept_result) << "tombstoned reported failure";
+
+  std::string result;
+  ConsumeFd(std::move(output_fd), &result);
+
+  // The address can either be tagged (new kernels) or untagged (old kernels).
+  ASSERT_MATCH(
+      result,
+      R"(signal 11 \(SIGSEGV\), code 1 \(SEGV_MAPERR\), fault addr (0x100000000000dead|0xdead))");
+}
+
 TEST_F(CrasherTest, LD_PRELOAD) {
   int intercept_result;
   unique_fd output_fd;