Re: [kernel-hardening] [PATCH v5 06/10] arm64/mm: Disable section mappings if XPFO is enabled

Tycho Andersen
2017-08-14T20:28:48Z

On Mon, Aug 14, 2017 at 11:42:45AM -0700, Laura Abbott wrote:
> On 08/14/2017 09:22 AM, Tycho Andersen wrote:
> > On Sat, Aug 12, 2017 at 12:17:34PM +0100, Mark Rutland wrote:
> >> Hi,
> >>
> >> On Fri, Aug 11, 2017 at 03:13:02PM -0600, Tycho Andersen wrote:
> >>> On Fri, Aug 11, 2017 at 10:25:14AM -0700, Laura Abbott wrote:
> >>>> On 08/09/2017 01:07 PM, Tycho Andersen wrote:
> >>>>> @@ -190,7 +202,7 @@ static void init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
> >>>>> next = pmd_addr_end(addr, end);
> >>>>>
> >>>>> /* try section mapping first */
> >>>>> - if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
> >>>>> + if (use_section_mapping(addr, next, phys) &&
> >>>>> (flags & NO_BLOCK_MAPPINGS) == 0) {
> >>>>> pmd_set_huge(pmd, phys, prot);
> >>>>>
> >>>>>
> >>>>
> >>>> There is already similar logic to disable section mappings for
> >>>> debug_pagealloc at the start of map_mem, can you take advantage
> >>>> of that?
> >>>
> >>> You're suggesting something like this instead? Seems to work fine.
> >>>
> >>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> >>> index 38026b3ccb46..3b2c17bbbf12 100644
> >>> --- a/arch/arm64/mm/mmu.c
> >>> +++ b/arch/arm64/mm/mmu.c
> >>> @@ -434,6 +434,8 @@ static void __init map_mem(pgd_t *pgd)
> >>>
> >>> if (debug_pagealloc_enabled())
> >>> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> >>> + if (IS_ENABLED(CONFIG_XPFO))
> >>> + flags |= NO_BLOCK_MAPPINGS;
> >>>
> >>
> >> IIUC, XPFO carves out individual pages just like DEBUG_PAGEALLOC, so you'll
> >> also need NO_CONT_MAPPINGS.
> >
> > Yes, thanks!
> >
> > Tycho
> >
>
> Setting NO_CONT_MAPPINGS fixes the TLB conflict aborts I was seeing
> on my machine.

Great, thanks for testing! I've also fixed the lookup_page_ext bug you
noted in the other thread.

Tycho