From: Florian Weimer <fweimer@redhat.com>
To: "Andy Lutomirski" <luto@kernel.org>
Cc: linux-arch@vger.kernel.org,
"Linux API" <linux-api@vger.kernel.org>,
linux-x86_64@vger.kernel.org,
kernel-hardening@lists.openwall.com, linux-mm@kvack.org,
"the arch/x86 maintainers" <x86@kernel.org>,
musl@lists.openwall.com,
"Dave Hansen via Libc-alpha" <libc-alpha@sourceware.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Dave Hansen" <dave.hansen@intel.com>,
"Kees Cook" <keescook@chromium.org>
Subject: [musl] Re: [PATCH] x86: Implement arch_prctl(ARCH_VSYSCALL_LOCKOUT) to disable vsyscall
Date: Thu, 16 Dec 2021 19:31:19 +0100 [thread overview]
Message-ID: <87czlwieq0.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <3b5fb404-7228-48d6-a290-9dd1d6095325@www.fastmail.com> (Andy Lutomirski's message of "Sat, 27 Nov 2021 20:45:23 -0800")
* Andy Lutomirski:
> This could possibly be much more generic: have a mask of legacy
> features to disable and a separate mask of lock bits.
Is that really necessary? Adding additional ARCH_* constants does not
seem to be particularly onerous and helps with detection of kernel
support.
>> I can turn this into a toggle, and we could probably default our builds
>> to vsyscalls=xonly. Given the userspace ABI impact, we'd still have to
>> upstream the toggle. Do you see a chance of a patch a long these lines
>> going in at all, given that it's an incomplete solution for
>> vsyscall=emulate?
>
> There is basically no reason for anyone to use vsyscall=emulate any
> more. I'm aware of exactly one use case, and it's quite bizarre and
> involves instrumenting an outdated binary with an outdated
> instrumentation tool. If either one is recent (last few years),
> vsyscall=xonly is fine.
Yeah, we plan to stick to vsyscall=xonly. This means that the toggle is
easier to implement, of course.
>> Hmm. But only for vsyscall=xonly, right? With vsyscall=emulate,
>> reading at those addresses will still succeed.
>
> IMO if vsyscall is disabled for a process, reads and executes should
> both fail. This is trivial in xonly mode.
Right, I'll document this as a glitch for now.
I've got a v2 (with the toggle rather than pure lockout) and will sent
it out shortly.
Thanks,
Florian
prev parent reply other threads:[~2021-12-16 18:31 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-26 13:47 [musl] " Florian Weimer
2021-11-26 18:58 ` [musl] " Andy Lutomirski
2021-11-26 20:24 ` Florian Weimer
2021-11-26 22:53 ` Andy Lutomirski
2021-11-26 23:18 ` Florian Weimer
2021-11-28 4:45 ` Andy Lutomirski
2021-12-16 18:31 ` Florian Weimer [this message]
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