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From: "wilson at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/96191] aarch64 stack_protect_test canary leak
Date: Tue, 14 Jul 2020 22:30:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96191

--- Comment #3 from Jim Wilson <wilson at gcc dot gnu.org> ---
The location of the canary is not known to the attacker.  You are not suppo=
sed
to leak the address of the canary or the value of the canary.  If you leak
either, then an attacker has a chance to restore the canary after clobbering
it.

See the descriptions of the stack_protect_set and stack_protect_test patter=
ns
in gcc/doc/md.texi which make clear that no intermediate values should be
allowed to survive past the end of the pattern.=