From: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date: Wed, 15 Apr 2020 16:40:45 +0000 (+0100)
Subject: aarch64: redefine RETURN_ADDRESS to strip PAC
X-Git-Tag: glibc-2.32~93
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d174ec248d5b6bba3842f425f036495b682c313f;p=thirdparty%2Fglibc.git

aarch64: redefine RETURN_ADDRESS to strip PAC

RETURN_ADDRESS is used at several places in glibc to mean a valid
code address of the call site, but with pac-ret it may contain a
pointer authentication code (PAC), so its definition is adjusted.

This is gcc PR target/94891: __builtin_return_address should not
expose signed pointers to user code where it can cause ABI issues.
In glibc RETURN_ADDRESS is only changed if it is built with pac-ret.
There is no detection for the specific gcc issue because it is
hard to test and the additional xpac does not cause problems.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
---

diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index f442506952a..ae269146e3a 100644
--- a/sysdeps/aarch64/sysdep.h
+++ b/sysdeps/aarch64/sysdep.h
@@ -44,6 +44,13 @@ strip_pac (void *p)
   asm ("hint 7 // xpaclri" : "+r"(ra));
   return ra;
 }
+
+/* This is needed when glibc is built with -mbranch-protection=pac-ret
+   with a gcc that is affected by PR target/94891.  */
+# if HAVE_AARCH64_PAC_RET
+#  undef RETURN_ADDRESS
+#  define RETURN_ADDRESS(n) strip_pac (__builtin_return_address (n))
+# endif
 #endif
 
 #ifdef	__ASSEMBLER__