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Re: Gold Linker Patch: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715 and in some places called "spectre".

From: "Sriraman Tallam via binutils" <binutils at sourceware dot org>
To: Cary Coutant <ccoutant at gmail dot com>
Cc: binutils <binutils at sourceware dot org>, Chandler Carruth <chandlerc at google dot com>, Reid Kleckner <rnk at google dot com>, Eric Christopher <echristo at google dot com>, Rui Ueyama <ruiu at google dot com>, Brooks Moses <bmoses at google dot com>, Sidney Hummert <shummert at google dot com>, Xinliang David Li <davidxl at google dot com>
Date: Thu, 4 Jan 2018 16:35:17 -0800
Subject: Re: Gold Linker Patch: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715 and in some places called "spectre".
Authentication-results: sourceware.org; auth=none
References: <CAAs8HmzJkLiGaUWf9czpNfEejM=uCP=zFvudADEuxsA2wHk+fQ@mail.gmail.com> <CAJimCsGGcXCxQUWD9XGmEHdJ+w01Tr0u29yowA9b16YGHHxMkA@mail.gmail.com>
Reply-to: Sriraman Tallam <tmsriram at google dot com>

Hi Cary,

  Thanks for reviewing.

On Thu, Jan 4, 2018 at 3:08 PM, Cary Coutant <ccoutant@gmail.com> wrote:
>> * options.h (retpolineplt): New -z option to use retpoline PLT.
>> * x86_64.cc (Output_data_plt_x86_64_retpoline): New class.
>> (Target_x86_64<64>::do_make_data_plt): Create retpoline PLT when
>> the option is used.
>> * testsuite/Makefile.am (retpoline_plt_1.sh): New test.
>> * testsuite/Makefile.in: Regenerate.
>> * testsuite/retpoline_plt_1.sh: New test script.
>> * testsuite/retpoline_plt_1.s: New test source.
>
> This makes the -z bndplt and -z retpolineplt options mutually
> exclusive. Please add a check in options.cc
> (General_options::finalize) for this.

Done and new patch attached.

* options.h (retpolineplt): New -z option to use retpoline PLT.
* options.cc (General_options::finalize): Check if both retpolineplt
and bndplt are turned on.
* x86_64.cc (Output_data_plt_x86_64_retpoline): New class.
(Target_x86_64<64>::do_make_data_plt): Create retpoline PLT when
the option is used.
* testsuite/Makefile.am (retpoline_plt_1.sh): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/retpoline_plt_1.sh: New test script.
* testsuite/retpoline_plt_1.s: New test source.

>
> Will we be seeing an aarch64 patch along these same lines soon? As I
> understand it, 64-bit ARM is susceptible to Spectre, but 32-bit ARM is
> not (because 32-bit chips don't do any OOO execution). I haven't seen
> a clear statement about other architectures like Sparc and PPC.

retpoline is currently an x86-specific mitigation. Other architectural
mitigations may be forthcoming, but I'm not actively working on them.

Thanks
Sri

>
> -cary

Attachment: retpoline_plt_patch.txt
Description: Text document

Follow-Ups:
- Re: Gold Linker Patch: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715 and in some places called "spectre".
  - From: Cary Coutant

References:
- Re: Gold Linker Patch: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715 and in some places called "spectre".
  - From: Cary Coutant

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