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

Laura Abbott
2017-08-11T17:25:19Z

On 08/09/2017 01:07 PM, Tycho Andersen wrote:
> From: Juerg Haefliger <juerg.haefliger@hpe.com>
>
> XPFO (eXclusive Page Frame Ownership) doesn't support section mappings
> yet, so disable it if XPFO is turned on.
>
> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
> Tested-by: Tycho Andersen <tycho@docker.com>
> ---
> arch/arm64/mm/mmu.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index f1eb15e0e864..38026b3ccb46 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -176,6 +176,18 @@ static void alloc_init_cont_pte(pmd_t *pmd, unsigned long addr,
> } while (addr = next, addr != end);
> }
>
> +static inline bool use_section_mapping(unsigned long addr, unsigned long next,
> + unsigned long phys)
> +{
> + if (IS_ENABLED(CONFIG_XPFO))
> + return false;
> +
> + if (((addr | next | phys) & ~SECTION_MASK) != 0)
> + return false;
> +
> + return true;
> +}
> +
> static void init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
> phys_addr_t phys, pgprot_t prot,
> phys_addr_t (*pgtable_alloc)(void), int flags)
> @@ -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?

Thanks,
Laura