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Re: [PATCH 0/5] x86: CVE-2017-5715, aka Spectre
On Sun, Jan 14, 2018 at 6:20 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> > Hi HJ,
>> >
>> > > -----Original Message-----
>> > > From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
>> > > owner@gcc.gnu.org] On Behalf Of H.J. Lu
>> > > Sent: Sunday, January 14, 2018 9:07 AM
>> > > To: gcc-patches@gcc.gnu.org
>> > > Subject: [PATCH 0/5] x86: CVE-2017-5715, aka Spectre
>> > >
>> > > This set of patches for GCC 8 mitigates variant #2 of the speculative
>> > > execution vulnerabilities on x86 processors identified by CVE-2017-5715, aka
>> > > Spectre. They convert indirect branches and function returns to call and
>> > > return thunks to avoid speculative execution via indirect call, jmp and ret.
>> > >
>> > > H.J. Lu (5):
>> > > x86: Add -mindirect-branch=
>> > > x86: Add -mfunction-return=
>> > > x86: Add -mindirect-branch-register
>> > > x86: Add 'V' register operand modifier
>> > > x86: Disallow -mindirect-branch=/-mfunction-return= with
>> > > -mcmodel=large
>> >
>> > Current set of patches don't seem to have any option to generate "lfence" as the loop filler in "retpoline", which is required by AMD.
>> > Can you please clarify the plan. We would like to get this checked-in GCC 8.
>>
>> Since thunks are output as strings, it is easy to add the option
>> on the top of patch #1 of the series. I do not fully understand
>> the reason for choosing pause over lfence for Intel, but if we need
>> to do both, we need to have command line option (and possibly attribute).
>> What would be reasonable name for it?
>
> I forgot there is -mindirect-branch-loop for that in the original patchset.
> So for now we should be happy with having both lfence and pause in there
> or do we still need it?
>
I suggest we leave it out for the time being.
--
H.J.