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

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Message-ID: <20110531193602.GA26535@elte.hu>
Date:	Tue, 31 May 2011 21:36:02 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Lutomirski <luto@....edu>
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


* 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.

Thanks,

	Ingo
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