linux-kernel - Re: [PATCH v3 10/10] x86-64: Add CONFIG_UNSAFE

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Date:	Sat, 6 Aug 2011 16:18:38 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Lutomirski <luto@....edu>, Andi Kleen <andi@...stfloor.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <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>
Subject: Re: [PATCH v3 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

On Tuesday, May 31, 2011, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Ingo Molnar <mingo@...e.hu> wrote:
>
>> [...] solution that filters the caller RIP at the generic syscall
>> entry point and checks RCX against the 'expected' SYSCALL
>> instruction address, which is the (per task) vdso-address +
>> constant-offset.
>
> Note that this solution would allow the vsyscall page to be
> 'filtered' to the 3 allowed system calls rather efficiently, via a
> second level check.
>
> This second check does not affect the fastpath, and it could be put
> behind a CONFIG_COMPAT_VSYSCALL deprecation define once glibc does
> not put vsyscall references anywhere - but we could even keep it
> around forever, as this way it's defanged permanently.

I'm confused.  Are you thinking about the 32-bit vDSO?  I think that
64-bit code puts syscall instructions all over the place.

--Andy

>
> Thanks,
>
>         Ingo
>
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