On Wed, Nov 4, 2015 at 5:06 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Wed, Nov 4, 2015 at 5:00 PM, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx> >> --- >> 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>