netdev - Re: [PATCH net] bpf: disable broken write protection on i386

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Date:   Wed, 8 Mar 2017 10:40:14 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH net] bpf: disable broken write protection on i386

On Mon, Mar 6, 2017 at 10:11 AM, Kees Cook <keescook@...omium.org> wrote:
> On Fri, Mar 3, 2017 at 7:23 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
>> Latter shows that memory protecting the kernel seems not working either
>> on i386 (!). Test suite output:
>>
>>   [...]
>>   [   12.692836] Write protecting the kernel text: 13416k
>>   [   12.693309] Write protecting the kernel read-only data: 5292k
>>   [   12.693802] rodata_test: test data was not read only
>>   [...]
>>
>> Work-around to not enable ARCH_HAS_SET_MEMORY for i386 is not optimal
>> as it doesn't fix the issue in presumably broken set_memory_*(), but
>> it at least avoids people avoid having to deal with random corruptions
>> that are hard to track down for the time being until a real fix can
>> be found.
>
> Wow. Uhm, so, something must be _really_ broken. i386 should have no
> problem with using the set_memory_*() functions. The fact that
> DEBUG_RODATA_TEST failed is also pretty crazy, but may be unrelated
> (that test was just refactored too).

I'm not able to reproduce this. I built Linus's tree and rodata_test
passes for me on i386. I tried the .config from Fengguang (with
RODATA_TEST=y added), but it still passes for me:
https://lkml.org/lkml/2017/3/1/344

I wonder if something change changed already in the tree? Can you
still reproduce this?

-Kees

-- 
Kees Cook
Pixel Security