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Subject: Re: New vsyscall emulation breaks JITs
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Tue, 09 Aug 2011 19:56:47 -0500
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Lutomirski <luto@mit.edu>
CC: Greg Lueck <lueckintel@yahoo.com>, Andi Kleen <andi@firstfloor.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kimwooyoung@gmail.com" <kimwooyoung@gmail.com>
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Linus Torvalds <torvalds@linux-foundation.org> wrote:

>On Tue, Aug 9, 2011 at 2:04 PM, Andrew Lutomirski <luto@mit.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.
-- 
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