linux-kernel - Re: [RFC] x86: xsave/xrstor support, ucontext

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Message-ID: <18485.61966.193804.314820@harpo.it.uu.se>
Date:	Fri, 23 May 2008 00:22:06 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>, mingo@...e.hu,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, roland@...hat.com, drepper@...hat.com,
	Hongjiu.lu@...el.com, linux-kernel@...r.kernel.org,
	arjan@...ux.intel.com, rmk+lkml@....linux.org.uk, dan@...ian.org,
	asit.k.mallick@...el.com
Subject: Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

H. Peter Anvin writes:
 > > But user can potentially change the _fpstate pointer in sigcontext struct.
 > 
 > If so, they get what they bargained for... I am not even sure the kernel 
 > will successfully clean up the stack frame if they do that.

Why would that be a problem? The stack is defined by the user's SP,
which is in the integer state part of the sigframe. We do a sigreturn(),
reload SP/PC/etc, and off we go. Where fpstate pointed to doesn't matter,
as long as it was NULL or a valid fpstate image.
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