From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Jan Kratochvil <jkratochvil@azul.com>
Cc: Florian Weimer <fweimer@redhat.com>,
libc-alpha@sourceware.org, Anton Kozlov <akozlov@azul.com>
Subject: Re: [PATCH] RFC: Provide a function to reset IFUNC PLTs
Date: Wed, 8 Mar 2023 10:04:59 -0300 [thread overview]
Message-ID: <c0c90262-c1c2-4ad4-109b-5b80119b3b8a@linaro.org> (raw)
In-Reply-To: <ZAhhnpdGsI4hLlp9@host1.jankratochvil.net>
On 08/03/23 07:21, Jan Kratochvil wrote:
> On Tue, 07 Mar 2023 21:07:58 +0800, Adhemerval Zanella Netto wrote:
>> 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).
>
> You are right but I left the thread safety up to the caller ("Freezer"):
> https://github.com/openjdk/crac/pull/41/files#diff-aeec57d804d56002f26a85359fc4ac8b48cfc249d57c656a30a63fc6bf3457adR6029
>
> It could be moved to the glibc part.
>
>
>> 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).
>
> RELRO is removed only temporarily, it gets re-engaged. And that time other
> threads should be even stopped (see above). Is it still a security issues?
Yes, without a stop-the-world scheme where a helper thread sets PR_GET_DUMPABLE
and PTRACE_ATTACH the process can not really be sure that any new thread will not
be created between the time you enumerate the process threads and call the 'freeze'
function.
I really don't think glibc should provide an interface to temporary disable any
security hardening, it should always opt-in at either program startup or by
building time. The ifunc mechanism is already full or corner cases and I think
adding a runtime mechanism to reset them is *not* a way forward.
As I said, I think CRIU heterogeneity should be handled by masking off the higher
cpu features. I am not if ARCH_SET_CPUID would a solution here, it means that
we will need to handle SIGSEGV in the loader and come up with a sane subset
in case of failure (we now have x86_64-vx, so we can use it as default).
But as Florian has said, fixing on glibc won't work consistently on other
libraries that uses cpuid instruction. And yes, I am aware we are discussing
glibc, but I prefer a composable solution (like adding proper cpuid maskoff in
the kernel) to add an ah-hoc one.
next prev parent reply other threads:[~2023-03-08 13:05 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
2023-03-08 10:21 ` Jan Kratochvil
2023-03-08 13:04 ` Adhemerval Zanella Netto [this message]
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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