On Tue 08-05-18 09:27:45, Huang, Ying wrote:
> From: Huang Ying <ying.hu...@intel.com>
>
> In ab676b7d6fbf ("pagemap: do not leak physical addresses to
> non-privileged userspace"), the /proc/PID/pagemap is restricted to be
> readable only by CAP_SYS_ADMIN to address some security issue. In
> 1c90308e7a77 ("pagemap: hide physical addresses from non-privileged
> users"), the restriction is relieved to make /proc/PID/pagemap
> readable, but hide the physical addresses for non-privileged users.
> But the swap entries are readable for non-privileged users too. This
> has some security issues. For example, for page under migrating, the
> swap entry has physical address information. So, in this patch, the
> swap entries are hided for non-privileged users too.
Migration entries are quite ephemeral so I am not sure how this could be
abused. But I do agree that hiding swap entries make some sense from
consistency POV
> Fixes: 1c90308e7a77 ("pagemap: hide physical addresses from non-privileged
> users")
> Signed-off-by: "Huang, Ying" <ying.hu...@intel.com>
> Suggested-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
> Cc: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
> Cc: Andrei Vagin <ava...@openvz.org>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: Jerome Glisse <jgli...@redhat.com>
> Cc: Daniel Colascione <dan...@google.com>
> Cc: Zi Yan <zi....@cs.rutgers.edu>
> Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
Acked-by: Michal Hocko <mho...@suse.com>
> ---
> fs/proc/task_mmu.c | 26 ++++++++++++++++----------
> 1 file changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index a20c6e495bb2..ff947fdd7c71 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1258,8 +1258,9 @@ static pagemap_entry_t pte_to_pagemap_entry(struct
> pagemapread *pm,
> if (pte_swp_soft_dirty(pte))
> flags |= PM_SOFT_DIRTY;
> entry = pte_to_swp_entry(pte);
> - frame = swp_type(entry) |
> - (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
> + if (pm->show_pfn)
> + frame = swp_type(entry) |
> + (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
> flags |= PM_SWAP;
> if (is_migration_entry(entry))
> page = migration_entry_to_page(entry);
> @@ -1310,11 +1311,14 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned
> long addr, unsigned long end,
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> else if (is_swap_pmd(pmd)) {
> swp_entry_t entry = pmd_to_swp_entry(pmd);
> - unsigned long offset = swp_offset(entry);
> + unsigned long offset;
>
> - offset += (addr & ~PMD_MASK) >> PAGE_SHIFT;
> - frame = swp_type(entry) |
> - (offset << MAX_SWAPFILES_SHIFT);
> + if (pm->show_pfn) {
> + offset = swp_offset(entry) +
> + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> + frame = swp_type(entry) |
> + (offset << MAX_SWAPFILES_SHIFT);
> + }
> flags |= PM_SWAP;
> if (pmd_swp_soft_dirty(pmd))
> flags |= PM_SOFT_DIRTY;
> @@ -1332,10 +1336,12 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned
> long addr, unsigned long end,
> err = add_to_pagemap(addr, &pme, pm);
> if (err)
> break;
> - if (pm->show_pfn && (flags & PM_PRESENT))
> - frame++;
> - else if (flags & PM_SWAP)
> - frame += (1 << MAX_SWAPFILES_SHIFT);
> + if (pm->show_pfn) {
> + if (flags & PM_PRESENT)
> + frame++;
> + else if (flags & PM_SWAP)
> + frame += (1 << MAX_SWAPFILES_SHIFT);
> + }
> }
> spin_unlock(ptl);
> return err;
> --
> 2.17.0
>
--
Michal Hocko
SUSE Labs
