Re: [PATCH v3 2/2] x86/refcount: Implement fast refcount overflow protection

[Josh Poimboeuf]

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@xxxxxxxxxx> 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