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Date:   Wed, 8 Mar 2017 21:36:01 -0800
From:   Kees Cook <>
To:     Laura Abbott <>
Cc:     Daniel Borkmann <>,
        Linus Torvalds <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Peter Anvin <>,
        Fengguang Wu <>,
        Network Development <>,
        LKML <>, LKP <>,, "the arch/x86 maintainers" <>,
        "David S. Miller" <>
Subject: Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request
 at 0000a7cf

On Wed, Mar 8, 2017 at 3:55 PM, Laura Abbott <> wrote:
> On 03/08/2017 02:36 PM, Kees Cook wrote:
>> On Wed, Mar 8, 2017 at 2:27 PM, Daniel Borkmann <> wrote:
>>> [   28.474232] rodata_test: test data was not read only
>>> [...]
>> In my tests so far, I've never been able to get rodata_test to fail
>> (Qemu 2.5.0, Ubuntu). I'll retry with your .config and see if I can
>> recheck under Qemu 2.7.1. Do you see these failures on real hardware?
>> -Kees
> FWIW, I'm seeing the same issue with qemu 2.6.2 and 2.8.0 on Fedora 24
> and rawhide respectively.
> I also notice that CONFIG_X86_PAE is turned off in the defconfig. If
> I set CONFIG_HIGHMEM_64G which turns on CONFIG_X86_PAE the problem
> goes away. I can't tell if this is an indication of magically hiding
> the TLB problem or if there is an issue with !X86_PAE invalidation.

I found my difference. I normally run qemu with "-cpu host" which
makes the failure go away. With "-cpu kvm64", I see the rodata_test
failure immediately. Seems like this may be a kvm cpu feature
emulation bug? I'll see if I can find the specific cpu feature in the


Kees Cook
Pixel Security

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