Reland "[ASan] Do not misrepresent high value address dereferences as null dereferences"

Updated: Removed offending TODO comment.

Dereferences with addresses above the 48-bit hardware addressable range
produce "invalid instruction" (instead of "invalid access") hardware
exceptions (there is no hardware address decoding logic for those bits),
and the address provided by this exception is the address of the
instruction (not the faulting address).  The kernel maps the "invalid
instruction" to SEGV, but fails to provide the real fault address.

Because of this ASan lies and says that those cases are null
dereferences.  This downgrades the severity of a found bug in terms of
security.  In the ASan signal handler, we can not provide the real
faulting address, but at least we can try not to lie.

rdar://50366151

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D68676

llvm-svn: 374265

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@374384 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/sanitizer_common/sanitizer_linux.cpp b/lib/sanitizer_common/sanitizer_linux.cpp
index d23009075..0b53da6c3 100644
--- a/lib/sanitizer_common/sanitizer_linux.cpp
+++ b/lib/sanitizer_common/sanitizer_linux.cpp
@@ -1849,6 +1849,12 @@ SignalContext::WriteFlag SignalContext::GetWriteFlag() const {
 #endif
 }
 
+bool SignalContext::IsTrueFaultingAddress() const {
+  auto si = static_cast<const siginfo_t *>(siginfo);
+  // SIGSEGV signals without a true fault address have si_code set to 128.
+  return si->si_signo == SIGSEGV && si->si_code != 128;
+}
+
 void SignalContext::DumpAllRegisters(void *context) {
   // FIXME: Implement this.
 }