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Date: Mon, 8 May 2017 20:58:29 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, PaX Team <pageexec@freemail.hu>,
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        <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH v3 2/2] x86/refcount: Implement fast refcount overflow
 protection
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On Mon, May 08, 2017 at 04:31:11PM -0700, Kees Cook wrote:
> On Mon, May 8, 2017 at 3:53 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Mon, May 08, 2017 at 12:32:52PM -0700, Kees Cook wrote:
> >> +#define REFCOUNT_EXCEPTION                           \
> >> +     "movl $0x7fffffff, %[counter]\n\t"              \
> >> +     "int $"__stringify(X86_REFCOUNT_VECTOR)"\n"     \
> >> +     "0:\n\t"                                        \
> >> +     _ASM_EXTABLE(0b, 0b)
> >
> > Despite the objtool warnings going away, this still uses the exception
> > table in a new way, which will confuse objtool.  I need to do some more
> > thinking about the best way to fix it, either as a change to your patch
> > or a change to objtool.
> 
> In that it's not a "true" exception?

Right.  And also that it doesn't need the "fixup" since it would return
to the same address anyway.

-- 
Josh