linux-kernel - Re: New vsyscall emulation breaks JITs

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Date:	Tue, 09 Aug 2011 19:56:47 -0500
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Lutomirski <luto@....edu>
CC:	Greg Lueck <lueckintel@...oo.com>,
	Andi Kleen <andi@...stfloor.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kimwooyoung@...il.com" <kimwooyoung@...il.com>
Subject: Re: New vsyscall emulation breaks JITs

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

>On Tue, Aug 9, 2011 at 2:04 PM, Andrew Lutomirski <luto@....edu> wrote:
>>
>> Here's a different proposal, then:
>>
>> What if the kernel had the sequence:
>>
>> mov $__NR_whatever,%eax
>> syscall
>> ret
>>
>> in the vsyscall page but marked the vsyscall page NX.
>
>This sounds like a sound idea. And then the difference between "fast
>and native" and "slow and trapping" ends up literally being just the
>NX bit.
>
>                        Linus

Very promising idea indeed.
-- 
Sent from my mobile phone. Please excuse my brevity and lack of formatting.
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