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Date:   Thu, 30 Aug 2018 07:21:18 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Rik van Riel <riel@...riel.com>,
        Jann Horn <jannh@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] x86/nmi: Fix some races in NMI uaccess



> On Aug 30, 2018, at 6:36 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
>> On Wed, 29 Aug 2018, Nadav Amit wrote:
>> at 8:47 AM, Andy Lutomirski <luto@...nel.org> wrote:
>> 
>>> In NMI context, we might be in the middle of context switching or in
>>> the middle of switch_mm_irqs_off().  In either case, CR3 might not
>>> match current->mm, which could cause copy_from_user_nmi() and
>>> friends to read the wrong memory.
>>> 
>>> Fix it by adding a new nmi_uaccess_okay() helper and checking it in
>>> copy_from_user_nmi() and in __copy_from_user_nmi()'s callers.
>>> 
>>> Cc: stable@...r.kernel.org
>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>> Cc: Nadav Amit <nadav.amit@...il.com>
>>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>>> ---
>>> 
>>> Nadav, this is intended for your series.  Want to add it right
>>> before the use_temporary_mm() stuff?
>> 
>> Sure. Thanks! I will apply the following small fix:
>> 
>>> +
>>> +#ifdef CONFIG_DEBUG_VM
>>> +    WARN_ON_ONCE(!loaded_mm);
>>> +#endif
>> 
>> Will be changed to VM_WARN_ON_ONCE() in the two instances.
> 
> Unless I'm completely lost, this can just be applied to tip right
> away. It's not depending on anything else.
> 

Fine with me. Do you want to do the VM_WARN_ON cleanup yourself or should I send a v3?

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