linux-kernel - Re: [RFC v2] x86-64: Allow emulated vsyscalls from user addresses

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Message-ID: <20110811131610.GA21916@ucw.cz>
Date:	Thu, 11 Aug 2011 15:16:10 +0200
From:	Pavel Machek <pavel@....cz>
To:	Andy Lutomirski <luto@....EDU>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, lueckintel@...oo.com,
	kimwooyoung@...il.com, Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC v2] x86-64: Allow emulated vsyscalls from user addresses

Hi!

> They trace control flow through the vsyscall page and recompile that
> code somewhere else.  Then they expect it to work.  DynamoRIO
> (http://dynamorio.org/) and Pin (http://www.pintool.org/) are
> affected.  They crash when tracing programs that use vsyscalls.
> Valgrind is smart enough not to cause problems.  It crashes on the
> getcpu vsyscall, but that has nothing to do with emulation.
> 
> This patch makes each of the three vsyscall entries use a different
> vector so that they can work when relocated.  It assumes that the
> code that relocates them is okay with the int instruction acting
> like ret.  DynamoRIO at least appears to work.

int acting as ret is seriously weird semantics. And no, invalid
syscall parameters will not cause segfault, just return of -EFAULT. So
... can this be changed?

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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