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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: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Florian Weimer <fweimer at redhat dot com>, Rui Ueyama <ruiu at google dot com>, Cary Coutant <ccoutant at gmail dot com>, Chandler Carruth <chandlerc at google dot com>, binutils <binutils at sourceware dot org>, Reid Kleckner <rnk at google dot com>, Eric Christopher <echristo 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>, Rahul Chaudhry <rahulchaudhry at google dot com>
- Date: Mon, 8 Jan 2018 13:23:57 -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> <17cb3295-626f-ba0f-7458-c13eaea24d2b@redhat.com> <CAJimCsE6bZ9VwKTfh9dFvT1HmNb==0Kxh6EJQQWXGoH-U=Epsg@mail.gmail.com> <CAGCO0KhMmBJXuWbb89ZG6tgpVHgmxkE5-xEmMikBjPkVQBDmPA@mail.gmail.com> <CAJimCsFh4c+JgR27i6kVEqexvbfkJJERZ7v7bp6b4JYbR2nUqg@mail.gmail.com> <CAAs8HmyztZxr64OF1q8Vuj=mBeAJXfRS7qssdADDiS5QA3sFpg@mail.gmail.com> <e7ca7f34-08bf-5024-568a-5f47e31a998a@redhat.com> <CAAs8HmxT_3nBxBhTGLARV8NX+G3K8SbH8_J9eGX8prmnibPm7Q@mail.gmail.com> <277ce2e7-88bf-b1ab-11e8-a9c53b6a9100@redhat.com> <CAAs8Hmzja3v9EZnLQSvS8P8NOQn3VHhYuOHAnFP-budxz+xghw@mail.gmail.com> <CAJENXguR9=L8zbGbttnLc_Up_ONh-diX1ULJvn7P5A9=9ebhOQ@mail.gmail.com> <d7a4f16b-f6e4-b489-a927-e31e13c8b23b@redhat.com> <CAAs8HmzBLo2O6Hrf7i7rbZ85tt+Ub4fRrn16OLPb4hGqGTtWsQ@mail.gmail.com> <CAMe9rOoQWmVTqrgaopogmebmL7cStms8pvqgtSyrDjG5ykDAVA@mail.gmail.com> <CAAs8HmzSTzkc1vnC8UMuYGMdq-gb1G5Z4A5PdON=JitC4MC2FA@mail.gmail.com> <CAMe9rOpKb+xgQfP=PM=p_q89edAts4n0qP8j271B2+vaEytWyQ@mail.gmail.com>
- Reply-to: Sriraman Tallam <tmsriram at google dot com>
On Mon, Jan 8, 2018 at 1:14 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Jan 8, 2018 at 1:09 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> On Mon, Jan 8, 2018 at 12:22 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Mon, Jan 8, 2018 at 12:17 PM, Sriraman Tallam via binutils
>>> <binutils@sourceware.org> wrote:
>>>> On Mon, Jan 8, 2018 at 11:01 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>>>> On 01/08/2018 07:51 PM, Rui Ueyama wrote:
>>>>>>
>>>>>> A drawback of using BIND_NOW is that an application that has a PLT entry
>>>>>> that cannot be resolved but not used fails to start with that option.
>>>>>
>>>>>
>>>>> That can be a good or bad thing, depending on your perspective. With more
>>>>> and more use of symbol versioning, the point is increasingly moot because
>>>>> the set of symbol versions is not checked lazily.
>>>>
>>>> Ok, my attempt to summarize the discussions around this patch:
>>>>
>>>> a) We don't need this patch.
>>>> * We could deploy fno-plt and now binding and remove PLTs
>>>> altogether. We have to fix correctness issues related to these, like
>>>> the one Rui pointed out.
>>>
>>> What correctness issue?
>>
>> If a lazy bound symbol cannot be resolved and is not resolved at
>> run-time, now binding will expose the issue.
>
> Is this the missing definition issue? I won't call it as "correctness". I
> consider it as "abuse". It can even be a security issue when a program
> crashes unexpectedly due to the missing definition.
Agreed and I understood this was Florian's point about good and bad
based on perspective.
>
>>>
>>>> * One other pain point is we do have internally is we use a
>>>> configuration for tests where we build a number of shared objects and
>>>> keep the main binary pretty thin. We have explicitly disabled now
>>>> binding for this due to performance reasons, huge increase in the
>>>> number of dynamic relocations putting unacceptable overheads on our
>>>> distributed build system. We need to find a solution here.
>>>
>>> Have you measured performance impact of -fno-plt?
>>
>> I have conducted some experiments with fno-plt for binaries that
>> mostly statically linked with some hot calls to libc. fno-plt did
>> gives us 0.5 %- 1% improvements here and we have plans to turn this on
>> for performance sensitive binaries. fno-plt seems to help in reducing
>> iTLB misses when used in conjunction with kernel huge pages.
>
> So removing PLT isn't that bad for performance.
Yes, based on what I have seen so far.
>
>>>
>>>> * The compiler is eliminating indirect branches and calls
>>>> anyway, might as well do it with fno-plt also. With
>>>> -mindirect-branch=think this might also be unnecessary but LLVM
>>>> atleast does not support this yet.
>>>
>>> Shouldn't LLVM be fixed?
>>
>> Yes, I can take a look at fixing LLVM fo this.
>>
>
> I think you should experiment all options before changing PLT.
>
>
> --
> H.J.
- 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".
- 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".
- 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".
- 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: Chandler Carruth via binutils
- 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".
- 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
- 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".
- 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
- 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".
- 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
- 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: Rui Ueyama via binutils
- 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".
- 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
- 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".
- 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
- 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".