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Date:   Tue, 4 Apr 2017 17:22:27 -0700
From:   Linus Torvalds <>
To:     Kees Cook <>
Cc:     Tommi Rantala <>,
        Dave Jones <>,
        Linux-MM <>,
        LKML <>,
        Laura Abbott <>,
        Ingo Molnar <>,
        Josh Poimboeuf <>,
        Mark Rutland <>,
        Eric Biggers <>
Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78!

On Tue, Apr 4, 2017 at 3:55 PM, Linus Torvalds
<> wrote:
> I already explained what the likely fix is: make devmem_is_allowed()
> return a ternary value, so that those things that *do* read the BIOS
> area can just continue to do so, but they see zeroes for the parts
> that the kernel has taken over.

Actually, a simpler solution might be to

 (a) keep the binary value

 (b) remove the test for the low 1M

 (c) to avoid breakage, don't return _error_, but just always read zero

that also removes (or at least makes it much more expensive) a signal
of which pages are kernel allocated vs BIOS allocated.


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