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Date:   Wed, 29 Aug 2018 11:56:08 -0700
From:   Nadav Amit <>
To:     Andy Lutomirski <>,
Cc:     Borislav Petkov <>, Rik van Riel <>,
        Jann Horn <>,
        LKML <>,,
        Peter Zijlstra <>
Subject: Re: [PATCH v2] x86/nmi: Fix some races in NMI uaccess

at 8:47 AM, Andy Lutomirski <> 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:
> Cc: Peter Zijlstra <>
> Cc: Nadav Amit <>
> Signed-off-by: Andy Lutomirski <>
> ---
> 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:

> +
> +	WARN_ON_ONCE(!loaded_mm);
> +#endif

Will be changed to VM_WARN_ON_ONCE() in the two instances.


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