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

Mark Rutland
2017-08-12T11:17:43Z

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.

Thanks
Mark.