From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Florian Weimer <fweimer@redhat.com>,
Jan Kratochvil via Libc-alpha <libc-alpha@sourceware.org>
Cc: Jan Kratochvil <jkratochvil@azul.com>, Anton Kozlov <akozlov@azul.com>
Subject: Re: [PATCH] RFC: Provide a function to reset IFUNC PLTs
Date: Tue, 7 Mar 2023 10:07:58 -0300 [thread overview]
Message-ID: <2659aadc-6518-cc0e-d103-84eafcbdc3f9@linaro.org> (raw)
In-Reply-To: <87v8jdq7ht.fsf@oldenburg.str.redhat.com>
On 07/03/23 05:40, Florian Weimer via Libc-alpha wrote:
> * Jan Kratochvil via Libc-alpha:
>
>> Some projects snapshot+restore process images to migrate them to
>> a different machine. The target machine may have different (particularly
>> lower) set of CPU features. Restored process does crash in glibc IFUNC
>> functions which have been already set in PLTs due to the former more
>> rich CPU features on the snapshotting machine.
>>
>> Providing a glibc function which can be called during the restore.
>>
>> I understand the code may need more adjustments before its upstreaming
>> but is this an acceptable approach?
>
> Do you have a high-level overview how this is supposed to work? Is CRIU
> expected to call the new _dl_reset_ifunc symbol after restore?
>
> Use of <sys/platform/x86.h> is somewhat rare. Not even GCC uses it
> AFAIK. It has its own cached CPU data used for target clones and
> similar features. Re-running those IFUNC resolvers will just give the
> same results.
I am not sure if the ifunc reset will be really safe without adding CRIU
migrate sync points, to avoid suspend execution in a context that the
ifunc variants are already being executed or its address is being in a
function point (for instance in PLT code).
Besides, I also not sure if adding way to remove RELRO protection won't
add more security issues (we can disable for sesuid binaries, but even
though it is not a good security practice).
>
> Distributions have started to deploy alternate builds in
> glibc-hwcaps/x86-64-v3 directories:
>
> openSUSE Tumbleweed gains optional x86-64-v3 optimization
> <https://news.opensuse.org/2023/03/02/tw-gains-optional-optimizations/>
>
> This might be a common situation fairly soon. This is not IFUNC-based
> at all, so any IFUNC-based approach is not going to help with that.
>
> Practically speaking, I think cluster heterogeneity needs to be hidden
> at the cluster level.
For glibc standpoint I think heterogeneity should be handled by masking
off the higher cpu features sets so the programs always run with the
lowest ifunc variants set.
next prev parent reply other threads:[~2023-03-07 13:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 8:04 Jan Kratochvil
2023-03-07 8:40 ` Florian Weimer
2023-03-07 13:07 ` Adhemerval Zanella Netto [this message]
2023-03-08 10:21 ` Jan Kratochvil
2023-03-08 13:04 ` Adhemerval Zanella Netto
2023-03-09 11:32 ` Jan Kratochvil
2023-03-09 15:47 ` Adhemerval Zanella Netto
2023-03-09 17:43 ` Adhemerval Zanella Netto
2023-03-16 14:38 ` Jan Kratochvil
2023-03-20 16:47 ` Adhemerval Zanella Netto
2023-03-29 12:12 ` Jan Kratochvil
2023-03-29 13:14 ` Adhemerval Zanella Netto
2023-03-13 13:59 ` Florian Weimer
2023-03-14 12:55 ` Jan Kratochvil
2023-03-14 14:49 ` Florian Weimer
2023-03-14 15:06 ` Jan Kratochvil
2023-03-08 10:23 ` Jan Kratochvil
2023-03-08 10:44 ` Florian Weimer
2023-03-08 11:03 ` Jan Kratochvil
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