linux-kernel - Re: [PATCH] x86/vsyscall: Remove CONFIG_LEGACY_VSYSCALL

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Message-Id: <7c87b9f7-0a26-41cf-ba34-3dbd37caa2b8@www.fastmail.com>
Date:   Wed, 11 May 2022 12:03:14 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Florian Weimer" <fweimer@...hat.com>
Cc:     "the arch/x86 maintainers" <x86@...nel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "Kees Cook" <keescook@...omium.org>
Subject: Re: [PATCH] x86/vsyscall: Remove CONFIG_LEGACY_VSYSCALL_EMULATE



On Wed, May 11, 2022, at 11:35 AM, Florian Weimer wrote:
> * Andy Lutomirski:
>
>> CONFIG_LEGACY_VSYSCALL_EMULATE is, as far as I know, only needed for the
>> combined use of exotic and outdated debugging mechanisms with outdated
>> binaries.  At this point, no one should be using it.  We would like to
>> implement dynamic switching of vsyscalls, but this is much more
>> complicated to support in EMULATE mode than XONLY mode.
>>
>> So let's force all the distros off of EMULATE mode.  If anyone actually
>> needs it, they can set vsyscall=emulate, and we can then get away with
>> refusing to support newer security models if that option is set.
>>
>> Cc: x86@...nel.org
>> Cc: Kees Cook <keescook@...omium.org>
>> Cc: Florian Weimer <fweimer@...hat.com>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>
> Sounds a good idea to me.
>
> Acked-by: Florian Weimer <fweimer@...hat.com>
>
> Regarding the mechanics, is it customary to remove the actual code (the
> EMULATE enum constant) in later commits?
>

Might be several versions later. This patch intentionally still supports booting with vsyscall=emulate.