Messages in this thread | | | Date | Wed, 4 Nov 2015 17:13:59 -0800 | Subject | Re: [PATCH] arm: Use kernel mm when updating section permissions | From | Kees Cook <> |
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On Wed, Nov 4, 2015 at 5:06 PM, Kees Cook <keescook@chromium.org> wrote: > On Wed, Nov 4, 2015 at 5:00 PM, Laura Abbott <labbott@fedoraproject.org> wrote: >> Currently, read only permissions are not being applied even >> when CONFIG_DEBUG_RODATA is set. This is because section_update >> uses current->mm for adjusting the page tables. current->mm >> need not be equivalent to the kernel version. Use pgd_offset_k >> to get the proper page directory for updating. >> >> Signed-off-by: Laura Abbott <labbott@fedoraproject.org> >> --- >> I found this while trying to convince myself of something. >> Dumping the page table via debugfs and writing to kernel text were both >> showing the lack of mappings. This was observed on QEMU. Maybe it's just a >> QEMUism but if not it probably should go to stable. > > Well that's weird! debugfs showed the actual permissions that lacked > RO? I wonder what changed. I tested this both with debugfs and lkdtm's > KERN_WRITE test when the patches originally landed.
The comment will need adjusting too. I have a memory of needing to use current->mm to deal with some crazy errata and handling TLB flushes...
-Kees
-- Kees Cook Chrome OS Security
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