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

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Message-ID: <4d4c4f1f-72e3-0182-151e-8bd455ccd143@zytor.com>
Date:   Mon, 26 Nov 2018 11:49:37 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     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,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/fpu: XRSTOR is expected to raise #GP

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.

	-hpa