linux-kernel - Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE

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Message-ID: <BANLkTinQ-y-g_3OKOWwOJ-sWxjJgh_G-=Q@mail.gmail.com>
Date:	Tue, 31 May 2011 16:05:07 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, 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>
Subject: Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

[Sorry, possible resend.]

On 5/31/11, 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.
>

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

How is this better than v2 of my series, stopping after the int cc fallback?

--Andy

> Thanks,
>
> 	Ingo
>
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