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: Re: [PATCH v3 3/3] x86: Add test for arch_prctl(ARCH_VSYSCALL_CONTROL)
References: <3a1c8280967b491bf6917a18fbff6c9b52e8df24.1641398395.git.fweimer@redhat.com>
        <54ae0e1f8928160c1c4120263ea21c8133aa3ec4.1641398395.git.fweimer@redhat.com>
        <564ba9d6b8f88d139be556d039aadb4b8e078eba.1641398395.git.fweimer@redhat.com>
        <4db8cff9-8bf8-0c45-6956-4b1b19b53b2f@kernel.org>
Date:   Thu, 13 Jan 2022 22:57:20 +0100
In-Reply-To: <4db8cff9-8bf8-0c45-6956-4b1b19b53b2f@kernel.org> (Andy
        Lutomirski's message of "Thu, 13 Jan 2022 13:31:04 -0800")
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* Andy Lutomirski:

> On 1/5/22 08:03, Florian Weimer wrote:
>> Signed-off-by: Florian Weimer <fweimer@redhat.com>
>
> This seems like a respectable test case, but why does it work so hard
> to avoid using libc?

Back when this was still a true lockout and not a toggle, it was
necessary to bypass the startup code, so that the test still works once
the (g)libc startup starts activating the lockout.  The /proc mounting
is there to support running as init in a VM (which makes development so
much easier).

I could ditch the /proc mounting, perform some limited data gathering in
a pre-_start routine, undo a potential lockout before the tests, and
then use libc functions for the actual test.  It would probably be a bit
less code (printf is nice), but I'd probably have to use direct system
calls for the early data gathering anyway, so those parts would still be
there.

Thanks,
Florian