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Message-ID: <20170719195249.akr6m2x65mhtsyvf@treble>
Date: Wed, 19 Jul 2017 14:52:49 -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 12:45:19PM -0700, Kees Cook wrote:
> > diff --git a/arch/x86/include/asm/refcount.h b/arch/x86/include/asm/refcount.h
> > index 13b91e850a02..e7587db3487c 100644
> > --- a/arch/x86/include/asm/refcount.h
> > +++ b/arch/x86/include/asm/refcount.h
> > @@ -15,6 +15,7 @@
> > ".pushsection .text.unlikely\n" \
> > "111:\tlea %[counter], %%" _ASM_CX "\n" \
> > "112:\t" ASM_UD0 "\n" \
> > + ASM_UNREACHABLE \
> > ".popsection\n" \
> > "113:\n" \
> > _ASM_EXTABLE_REFCOUNT(112b, 113b)
> > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> > index cd4bbe8242bd..85e0b8f42ca0 100644
> > --- a/include/linux/compiler-gcc.h
> > +++ b/include/linux/compiler-gcc.h
> > @@ -202,15 +202,25 @@
> > #endif
> >
> > #ifdef CONFIG_STACK_VALIDATION
> > +
> > #define annotate_unreachable() ({ \
> > asm("%c0:\t\n" \
> > - ".pushsection .discard.unreachable\t\n" \
> > - ".long %c0b - .\t\n" \
> > - ".popsection\t\n" : : "i" (__LINE__)); \
> > + ".pushsection .discard.unreachable\n\t" \
> > + ".long %c0b - .\n\t" \
> > + ".popsection\n\t" : : "i" (__LINE__)); \
>
> Is this just an indentation change?
This was sneaking in a fix to put the tab after the newline instead of
before it. I figured it's not worth its own commit.
> > })
> > +
> > +#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.
--
Josh
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