From: H.J. Lu <hongjiu.lu@intel.com>
Date: Thu, 26 Jul 2018 14:48:55 +0000 (+0000)
Subject: libsanitizer: Mark REAL(swapcontext) with indirect_return attribute on x86
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=c83b4b824214039fea696083e6a888aa7c9063ce;p=gcc.git

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

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

	PR target/86560
	* asan/asan_interceptors.cc (swapcontext) Cherry-pick
	compiler-rt revision 337603.
	* sanitizer_common/sanitizer_internal_defs.h (__has_attribute):
	Likewise.

From-SVN: r263009
---

diff --git a/libsanitizer/ChangeLog b/libsanitizer/ChangeLog
index 80c3c0298dd..8e984f8b2e4 100644
--- a/libsanitizer/ChangeLog
+++ b/libsanitizer/ChangeLog
@@ -1,3 +1,11 @@
+2018-07-25  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR target/86560
+	* asan/asan_interceptors.cc (swapcontext) Cherry-pick
+	compiler-rt revision 337603.
+	* sanitizer_common/sanitizer_internal_defs.h (__has_attribute):
+	Likewise.
+
 2018-07-05  Jakub Jelinek  <jakub@redhat.com>
 
 	Revert
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.