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

On 03/08/2017 07:40 PM, Kees Cook wrote:

On Mon, Mar 6, 2017 at 10:11 AM, Kees Cook [off-list ref] wrote:

quoted

On Fri, Mar 3, 2017 at 7:23 PM, Daniel Borkmann [off-list ref] wrote:

quoted

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?

I'll answer in a bit an will move the discussion over to the other
thread on the same topic ("[net/bpf] 3051bf36c2 BUG: unable to handle
kernel paging request at 0000a7cf" [1]) with you, Laura and Dave in
Cc as well.

   [1] https://lkml.org/lkml/2017/3/8/620