On Mon, May 29, 2017 at 1:18 PM, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: > > > On 05/29/2017 01:02 PM, Dmitry Vyukov wrote: >> On Sat, May 27, 2017 at 12:10 AM, Kirill A. Shutemov >> <kirill@xxxxxxxxxxxxx> wrote: >>> On Thu, May 25, 2017 at 11:33:33PM +0300, Kirill A. Shutemov wrote: >>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>>> index 0bf81e837cbf..c795207d8a3c 100644 >>>> --- a/arch/x86/Kconfig >>>> +++ b/arch/x86/Kconfig >>>> @@ -100,7 +100,7 @@ config X86 >>>> select HAVE_ARCH_AUDITSYSCALL >>>> select HAVE_ARCH_HUGE_VMAP if X86_64 || X86_PAE >>>> select HAVE_ARCH_JUMP_LABEL >>>> - select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP >>>> + select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP && !X86_5LEVEL >>>> select HAVE_ARCH_KGDB >>>> select HAVE_ARCH_KMEMCHECK >>>> select HAVE_ARCH_MMAP_RND_BITS if MMU >>> >>> Looks like KASAN will be a problem for boot-time paging mode switching. >>> It wants to know CONFIG_KASAN_SHADOW_OFFSET at compile-time to pass to >>> gcc -fasan-shadow-offset=. But this value varies between paging modes... >>> >>> I don't see how to solve it. Folks, any ideas? >> >> +kasan-dev >> >> I wonder if we can use the same offset for both modes. If we use >> 0xFFDFFC0000000000 as start of shadow for 5 levels, then the same >> offset that we use for 4 levels (0xdffffc0000000000) will also work >> for 5 levels. Namely, ending of 5 level shadow will overlap with 4 >> level mapping (both end at 0xfffffbffffffffff), but 5 level mapping >> extends towards lower addresses. The current 5 level start of shadow >> is actually close -- 0xffd8000000000000 and it seems that the required >> space after it is unused at the moment (at least looking at mm.txt). >> So just try to move it to 0xFFDFFC0000000000? >> > > Yeah, this should work, but note that 0xFFDFFC0000000000 is not PGDIR aligned address. Our init code > assumes that kasan shadow stars and ends on the PGDIR aligned address. > Fortunately this is fixable, we'd need two more pages for page tables to map unaligned start/end > of the shadow. I think we can extend the shadow backwards (to the current address), provided that it does not affect shadow offset that we pass to compiler.
