On Wed, Jan 06, 2016 at 09:18:03PM +0100, Ard Biesheuvel wrote: > On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote: > > 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>: > >> The original x86_64-only version of KASAN mapped its zero page > >> read-only, but this got lost when the code was generalised and > >> ported to arm64, since, at the time, the PAGE_KERNEL_RO define > >> did not exist. It has been added to arm64 in the mean time, so > >> let's use it. > >> > > > > Read-only wasn't lost. Just look at the next line: > > zero_pte = pte_wrprotect(zero_pte); > > > > PAGE_KERNEL_RO is not available on all architectures, thus it would be better > > to not use it in generic code. > > OK, I didn't see that. For some reason, it is not working for me on > arm64, though. It's because the arm64 set_pte_at() doesn't bother checking for !PTE_WRITE to set PTE_RDONLY when mapping kernel pages. It works fine for user though. That's because usually all read-only kernel mappings already have PTE_RDONLY set via PAGE_KERNEL_RO. We may need to change the set_pte_at logic a bit to cover the above case. -- Catalin -- 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>