From: Florian Weimer <fw@deneb.enyo.de>
To: Daniel Micay <danielmicay@gmail.com>
Cc: Jann Horn <jann@thejh.net>, Kees Cook <keescook@chromium.org>,
kernel-hardening@lists.openwall.com,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>, Ingo Molnar <mingo@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH] fork: make whole stack_canary random
Date: Mon, 31 Oct 2016 22:10:41 +0100 [thread overview]
Message-ID: <87ins8rzqm.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <1477947674.8761.4.camel@gmail.com> (Daniel Micay's message of "Mon, 31 Oct 2016 17:01:14 -0400")
* Daniel Micay:
>> It makes a lot of sense on x86_64 where it means the canary is
>> still 56 bits. Also, you want -fstack-check for protecting again
>> stack overflows rather than stack *buffer* overflow. SSP won't
>> really help you in that regard. Sadly, while -fstack-check now
>> works well in GCC 6 with little performance cost, it's not really a
I think GCC still does not treat the return address push on
architectures which have such a CALL instruction as an implicit stack
probe.
>> complete feature (and Clang impls it as a no-op!).
How many guard pages at the end of the stack does the kernel
guarantee? I saw some -fstack-check-generated code which seemed to
jump over a single guard page.
The other thing I've seen which could impact the effectiveness of
-fstack-check: mmap *without* MAP_FIXED and a hint within stack
allocation can create a mapping inside the stack. That's rather
surprising, and I'm not sure if the net result is that there actually
is a guard page in all cases.
> Note: talking about userspace after the entropy bit. The kernel doesn't
> really -fstack-check, at least in even slightly sane code...
There used to be lots of discussions about kernel stack sizes ...
next prev parent reply other threads:[~2016-10-31 21:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-31 14:04 [PATCH] fork: make whole stack_canary random Jann Horn
2016-10-31 16:04 ` Kees Cook
2016-10-31 16:29 ` [kernel-hardening] " Jann Horn
2016-10-31 20:45 ` Florian Weimer
2016-10-31 20:55 ` Jann Horn
2016-10-31 20:56 ` Daniel Micay
2016-10-31 21:01 ` Daniel Micay
2016-10-31 21:10 ` Florian Weimer [this message]
2016-10-31 21:21 ` Daniel Micay
2016-10-31 21:38 ` Florian Weimer
2016-10-31 22:02 ` Daniel Micay
2016-10-31 22:11 ` Florian Weimer
2016-10-31 21:22 ` Jann Horn
2016-10-31 21:26 ` Daniel Micay
2016-10-31 21:26 ` Florian Weimer
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