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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,  libc-alpha@sourceware.org,
	linux-kernel@vger.kernel.org,
	 Dave Hansen <dave.hansen@intel.com>,
	 Kees Cook <keescook@chromium.org>,
	 Andrei Vagin <avagin@gmail.com>
Subject: [musl] Re: [PATCH v3 1/3] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall
Date: Fri, 14 Jan 2022 14:36:24 +0100	[thread overview]
Message-ID: <87sftqtp5z.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <e431fa42-26ec-8ac6-f954-e681b1e0e9a6@kernel.org> (Andy Lutomirski's message of "Thu, 13 Jan 2022 13:47:26 -0800")

* Andy Lutomirski:

> Is there a reason you didn't just change the check earlier in the
> function to:
>
> if (vsyscall_mode == NONE || current->mm->context.vsyscall_disabled)

Andrei requested that I don't print anything if vsyscall was disabled.

The original patch used a different message for better diagnostics.

> Also, I still think the prctl should not be available if
> vsyscall=emulate.  Either we should fully implement it or we should
> not implement.  We could even do:
>
> pr_warn_once("userspace vsyscall hardening request ignored because you
> have vsyscall=emulate.  Unless you absolutely need vsyscall=emulate, 
> update your system to use vsyscall=xonly.\n");
>
> and thus encourage good behavior.

I think there is still some hardening applied even with
vsyscall=emulate.  The question is what is more important: the
additional hardening, or clean, easily described behavior of the
interface.

Maybe ARCH_VSYSCALL_CONTROL could return different values based on to
what degree it could disable vsyscall?

The pr_warn_once does not seem particularly useful.  Anyone who upgrades
glibc and still uses vsyscall=emulate will see that, with no way to
disable it.

Thanks,
Florian


      reply	other threads:[~2022-01-14 13:36 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-05 16:02 [musl] " Florian Weimer
2022-01-05 16:03 ` [musl] [PATCH v3 2/3] selftests/x86/Makefile: Support per-target $(LIBS) configuration Florian Weimer
2022-01-05 16:03   ` [musl] [PATCH v3 3/3] x86: Add test for arch_prctl(ARCH_VSYSCALL_CONTROL) Florian Weimer
2022-01-13 21:31     ` [musl] " Andy Lutomirski
2022-01-13 21:57       ` Florian Weimer
2022-01-13 21:31   ` [musl] Re: [PATCH v3 2/3] selftests/x86/Makefile: Support per-target $(LIBS) configuration Andy Lutomirski
2022-01-13 22:00     ` Florian Weimer
2022-01-14  2:34       ` Andy Lutomirski
2022-01-14 13:28         ` Florian Weimer
2022-01-13 17:27 ` [musl] Re: [PATCH v3 1/3] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall Florian Weimer
2022-01-13 21:47 ` Andy Lutomirski
2022-01-14 13:36   ` Florian Weimer [this message]

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