libsanitizer: Mark REAL(swapcontext) with indirect_return attribute on x86

Message ID 20180720201148.GA31200@intel.com
State New
Headers show
Series
  • libsanitizer: Mark REAL(swapcontext) with indirect_return attribute on x86
Related show

Commit Message

H.J. Lu July 20, 2018, 8:11 p.m.
Cherry-pick compiler-rt revision 337603:

When shadow stack from Intel CET is enabled, the first instruction of all
indirect branch targets must be a special instruction, ENDBR.

lib/asan/asan_interceptors.cc has

...
  int res = REAL(swapcontext)(oucp, ucp);
...

REAL(swapcontext) is a function pointer to swapcontext in libc.  Since
swapcontext may return via indirect branch on x86 when shadow stack is
enabled, as in this case,

int res = REAL(swapcontext)(oucp, ucp);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^  This function may be
returned via an indirect branch.

Here compiler must insert ENDBR after call, like

call *bar(%rip)
endbr64

I opened an LLVM bug:

https://bugs.llvm.org/show_bug.cgi?id=38207

to add the indirect_return attribute so that it can be used to inform
compiler to insert ENDBR after REAL(swapcontext) call.  We mark
REAL(swapcontext) with the indirect_return attribute if it is available.

This fixed:

https://bugs.llvm.org/show_bug.cgi?id=38249

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D49608

OK for trunk?

H.J.
---
	PR target/86560
	* asan/asan_interceptors.cc (swapcontext): Call REAL(swapcontext)
	with indirect_return attribute on x86 if indirect_return attribute
	is available.
	* sanitizer_common/sanitizer_internal_defs.h (__has_attribute):
	New.
---
 libsanitizer/asan/asan_interceptors.cc                  | 8 ++++++++
 libsanitizer/sanitizer_common/sanitizer_internal_defs.h | 5 +++++
 2 files changed, 13 insertions(+)

-- 
2.17.1

Patch

diff --git a/libsanitizer/asan/asan_interceptors.cc b/libsanitizer/asan/asan_interceptors.cc
index a8f4b72723f..552cf9347af 100644
--- a/libsanitizer/asan/asan_interceptors.cc
+++ b/libsanitizer/asan/asan_interceptors.cc
@@ -267,7 +267,15 @@  INTERCEPTOR(int, swapcontext, struct ucontext_t *oucp,
   uptr stack, ssize;
   ReadContextStack(ucp, &stack, &ssize);
   ClearShadowMemoryForContextStack(stack, ssize);
+#if __has_attribute(__indirect_return__) && \
+    (defined(__x86_64__) || defined(__i386__))
+  int (*real_swapcontext)(struct ucontext_t *, struct ucontext_t *)
+    __attribute__((__indirect_return__))
+    = REAL(swapcontext);
+  int res = real_swapcontext(oucp, ucp);
+#else
   int res = REAL(swapcontext)(oucp, ucp);
+#endif
   // swapcontext technically does not return, but program may swap context to
   // "oucp" later, that would look as if swapcontext() returned 0.
   // We need to clear shadow for ucp once again, as it may be in arbitrary
diff --git a/libsanitizer/sanitizer_common/sanitizer_internal_defs.h b/libsanitizer/sanitizer_common/sanitizer_internal_defs.h
index edd6a21c122..4413a88bea0 100644
--- a/libsanitizer/sanitizer_common/sanitizer_internal_defs.h
+++ b/libsanitizer/sanitizer_common/sanitizer_internal_defs.h
@@ -104,6 +104,11 @@ 
 # define __has_feature(x) 0
 #endif
 
+// Older GCCs do not understand __has_attribute.
+#if !defined(__has_attribute)
+# define __has_attribute(x) 0
+#endif
+
 // For portability reasons we do not include stddef.h, stdint.h or any other
 // system header, but we do need some basic types that are not defined
 // in a portable way by the language itself.