[v4,11/12] aarch64: redefine RETURN_ADDRESS to strip PAC

Message ID e0f6a9d3ef8a6c0d7f3f7ee4c5a09cb722d2d04f.1591899092.git.szabolcs.nagy@arm.com
State Superseded
Headers show
  • aarch64: branch protection support
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Commit Message

Szabolcs Nagy June 12, 2020, 1:29 p.m.
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/95891: __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.
 sysdeps/aarch64/sysdep.h | 7 +++++++
 1 file changed, 7 insertions(+)



diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index 2879aeaa5c..593bdd35a2 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/95891.  */
+#  define RETURN_ADDRESS(n) strip_pac (__builtin_return_address (n))
+# endif
 #ifdef	__ASSEMBLER__