linux-kernel - Re: [PATCH v3 08/10] x86-64: Emulate legacy vsyscalls

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Message-ID: <BANLkTi=mhNZcTJvWdPLAbJFo383iRfucOg@mail.gmail.com>
Date:	Wed, 1 Jun 2011 08:36:20 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v3 08/10] x86-64: Emulate legacy vsyscalls

On Wed, Jun 1, 2011 at 7:54 AM, Brian Gerst <brgerst@...il.com> wrote:
> On Tue, May 31, 2011 at 9:16 AM, Andy Lutomirski <luto@....edu> wrote:
>> There's a fair amount of code in the vsyscall page.  It contains a
>> syscall instruction (in the gettimeofday fallback) and who knows
>> what will happen if an exploit jumps into the middle of some other
>> code.
>>
>> Reduce the risk by replacing the vsyscalls with short magic
>> incantations that cause the kernel to emulate the real vsyscalls.
>> These incantations are useless if entered in the middle.
>
> How about remapping the vsyscall page into a random page in the
> modules area, and make the fixed page simply have stubs that jump to
> the code in that page.  That would solve the fixed address syscall
> problem without any more overhead.

It wouldn't give any protection against local attacks, though.

--Andy

>
> --
> Brian Gerst
>
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