linux-kernel - Re: [PATCH v4 09/10] x86-64: Randomize int 0xcc magic al values at boot

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Date:	Tue, 31 May 2011 18:43:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Lutomirski <luto@....edu>
Cc:	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 v4 09/10] x86-64: Randomize int 0xcc magic al values at
 boot


* Andrew Lutomirski <luto@....edu> wrote:

> On Tue, May 31, 2011 at 11:56 AM, Andrew Lutomirski <luto@....edu> wrote:
> > We could scrap int 0xcc entirely and emulate on page fault, but that
> > is slower and has other problems (like breaking anything that thinks
> > it can look at a call target in a binary and dereference that
> > address).
> >
> > Here's a possibly dumb/evil idea:
> >
> > Put real syscalls in the vsyscall page but mark the page NX.  Then
> > emulate the vsyscalls on the PF_INSTR fault when userspace jumps to
> > the correct address but send SIGSEGV for the wrong address.
> >
> > Down side: it's even more complexity for the same silly case.
> 
> Scratch that.  It's incompatible with keeping time() fast for now.

If we can find another fault than #PF then it will be similarly fast 
to an INT $0xCC so please at least investigate this route.

Thanks,

	Ingo
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