On Mon, Jun 15, 2020 at 07:49:41PM +0000, Dexuan Cui wrote: > I did this experiment: > 1. export vmalloc_exec and ptdump_walk_pgd_level_checkwx. > 2. write a test module that calls them. > 3. It turns out that every call of vmalloc_exec() triggers such a warning. > > vmalloc_exec() uses PAGE_KERNEL_EXEC, which is defined as > (__PP|__RW| 0|___A| 0|___D| 0|___G) > > It looks the logic in note_page() is: for_each_RW_page, if the NX bit is > unset, > then report the page as an insecure W+X mapping. IMO this explains the > warning?
It does. But it also means every other user of PAGE_KERNEL_EXEC should trigger this, of which there are a few (kexec, tboot, hibernate, early xen pv mapping, early SEV identity mapping) We really shouldn't create mappings like this by default. Either we need to flip PAGE_KERNEL_EXEC itself based on the needs of the above users, or add another define to overload vmalloc_exec as there is no other user of that for x86.
