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From:   Florian Weimer <fweimer@redhat.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/vsyscall: Remove CONFIG_LEGACY_VSYSCALL_EMULATE
References: <898932fe61db6a9d61bc2458fa2f6049f1ca9f5c.1652290558.git.luto@kernel.org>
        <202205111104.464A6619@keescook>
Date:   Wed, 11 May 2022 20:36:48 +0200
In-Reply-To: <202205111104.464A6619@keescook> (Kees Cook's message of "Wed, 11
        May 2022 11:04:55 -0700")
Message-ID: <87k0ardigv.fsf@oldenburg.str.redhat.com>
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* Kees Cook:

> On Wed, May 11, 2022 at 10:38:53AM -0700, Andy Lutomirski wrote:
>> 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 combined use of exotic and outdated debugging mechanisms with outdated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@kernel.org
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Florian Weimer <fweimer@redhat.com>
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>
> Sounds legit! Can we switch the default to "none" while we're at it?

I think that's a userspace ABI break?

I do not have a *very* strong opinion about this.  For one thing, it
would be handy example to have that such deliberate  do actually
happen. 8-)

Thanks,
Florian