kernel-hardening - RE: [PATCH] x86/fpu: XRSTOR is expected to raise #GP

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Message-ID: <52276fe27116406eb601a99704459f80@AcuMS.aculab.com>
Date: Wed, 28 Nov 2018 15:27:28 +0000
From: David Laight <David.Laight@...LAB.COM>
To: "'H. Peter Anvin'" <hpa@...or.com>, Sebastian Andrzej Siewior
	<bigeasy@...utronix.de>, Jann Horn <jannh@...gle.com>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH] x86/fpu: XRSTOR is expected to raise #GP

From: H. Peter Anvin
> Sent: 26 November 2018 19:50
> On 11/26/18 9:49 AM, Sebastian Andrzej Siewior wrote:
> > On 2018-11-26 18:27:06 [+0100], Jann Horn wrote:
> >> commit 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess
> >> fixups") incorrectly replaced the fixup entry for XSTATE_OP with a
> >> user-#PF-only fixup. However, XRSTOR can also raise #GP when the supplied
> >> address points to userspace memory. Change it back.
> >
> > The #GP is raised if the xstate content is invalid. But I guess the
> > details don't matter.
> >
> >> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> >> Fixes: 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixups")
> >> Signed-off-by: Jann Horn <jannh@...gle.com>
> > Acked-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> >
> 
> It does matter -- please correct the patch description, or we might have some
> serious confusion at some arbitrary point in the future with the result that
> the bug gets re-introduced; it would not be the first time.

Better still note it in the code.

	David

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