linux-kernel - Re: New vsyscall emulation breaks JITs

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Date:	Fri, 05 Aug 2011 13:36:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	luto@....edu, x86@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, lueckintel@...oo.com,
	kimwooyoung@...il.com
Subject: Re: New vsyscall emulation breaks JITs

On 08/05/2011 01:26 PM, Andi Kleen wrote:
>> I have to say I believe that trying to JIT the vdso or vsyscall pages is
>> extremely dubious at best.  They are fundamentally different from normal
>> user space in that the kernel can muck with them any time, without
>> notifying userspace about it.  The other aspect of this is that this is
>> about the legacy vsyscall page, which we're trying to get rid of, partly
>> because of security problems.
> 
> There's clear evidence now you can't: it's used even by new binaries.

time() is not supported by vdso; this is a problem.  Getting rid of it
is a long-term thing.

	-hpa

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