[glibc/nsz/pacbti-v6] aarch64: redefine RETURN_ADDRESS to strip PAC
Szabolcs Nagy
nsz@sourceware.org
Wed Jul 1 14:33:54 GMT 2020
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3354b735255589858af1eaa23867c4f1ac0c65fb
commit 3354b735255589858af1eaa23867c4f1ac0c65fb
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date: Wed Apr 15 17:40:45 2020 +0100
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.
Diff:
---
sysdeps/aarch64/sysdep.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index 2879aeaa5c..48fa8e9e90 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__
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