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Date: Wed, 19 Jul 2017 18:01:29 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Christoph Hellwig <hch@...radead.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Jann Horn <jannh@...gle.com>, Eric Biggers <ebiggers3@...il.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Hans Liljestrand <ishkamiel@...il.com>,
Greg KH <gregkh@...uxfoundation.org>,
Alexey Dobriyan <adobriyan@...il.com>,
"Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com,
Davidlohr Bueso <dave@...olabs.net>,
Manfred Spraul <manfred@...orfullife.com>,
"axboe@...nel.dk" <axboe@...nel.dk>,
James Bottomley <James.Bottomley@...senpartnership.com>,
"x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
"David S. Miller" <davem@...emloft.net>,
Rik van Riel <riel@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v6 2/2] x86/refcount: Implement fast refcount overflow
protection
On Wed, Jul 19, 2017 at 03:50:14PM -0700, Kees Cook wrote:
> >> > })
> >> > +
> >> > +#define ASM_UNREACHABLE \
> >> > + "999: .pushsection .discard.unreachable\n\t" \
> >> > + ".long 999b - .\n\t" \
> >> > + ".popsection\n\t"
> >>
> >> Just so I understand, we'll get a single byte added for each exception
> >> case, but it'll get discarded during final link?
> >
> > I think it's four bytes actually, but yeah, the section gets stripped at
> > vmlinux link time.
>
> Right, yes.
>
> BTW, I think this needs compiler.h coverage instead of the #else in
> compiler-gcc.h (since it's different from how annotate_unreachable is
> used only in compiler-gcc.h. I'll adjust.
Ah, right. Sounds good.
> Also, in looking at CONFIG_STACK_VALIDATION, do you want it to just
> warn and skip, or do you want to error out the build if validation
> isn't available but it's in the .config?
I think the current warn and skip behavior is fine. It's usually not a
life-or-death matter, and if it is, you'll be checking the warnings
anyway.
--
Josh
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