Date: Mon, 24 Jul 2017 20:34:31 -0700 From: Kees Cook <keescook@...omium.org> To: Alexander Popov <alex.popov@...ux.com> Cc: Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Tycho Andersen <tycho@...ker.com>, PaX Team <pageexec@...email.hu> Subject: Re: [RFC][PATCH 2/2] arm64: Clear the stack On Mon, Jul 24, 2017 at 1:19 AM, Alexander Popov <alex.popov@...ux.com> wrote: > On 22.07.2017 03:23, Laura Abbott wrote: >> On 07/21/2017 09:56 AM, Alexander Popov wrote: >>> So let's keep it not to break CONFIG_SCHED_STACK_END_CHECK. >> >> That makes sense, good find! I wonder if CONFIG_SCHED_STACK_END_CHECK >> should go on the list of hardening options and/or if we can enhance >> it somehow? > > Do you mean this list? > http://www.kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings > >> I'm not sure why it requires two words though since the >> poison only seems to be 32-bits? > > On x86_64 end_of_stack() returns the pointer to unsigned long, so we need at > least 8 bytes to avoid breaking CONFIG_SCHED_STACK_END_CHECK. Don't know about 8 > more bytes. Seems like this should be a random value like the per-frame stack canary, but it looks like a relatively cheap check. It's probably not in the cache, though, since most stack operations should be pretty far from the end of the stack... -Kees -- Kees Cook Pixel Security
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