Re: [PATCH v4 4/5] pagemap: hide physical addresses from non-privileged users

Naoya Horiguchi
2015-07-21T08:36:11Z

On Tue, Jul 14, 2015 at 06:37:47PM +0300, Konstantin Khlebnikov wrote:
> This patch makes pagemap readable for normal users and hides physical
> addresses from them. For some use-cases PFN isn't required at all.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Fixes: ab676b7d6fbf ("pagemap: do not leak physical addresses to non-privileged userspace")
> Link: http://lkml.kernel.org/r/1425935472-17949-1-git-send-email-kirill@shutemov.name
> ---
> fs/proc/task_mmu.c | 25 ++++++++++++++-----------
> 1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 040721fa405a..3a5d338ea219 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -937,6 +937,7 @@ typedef struct {
> struct pagemapread {
> int pos, len; /* units: PM_ENTRY_BYTES, not bytes */
> pagemap_entry_t *buffer;
> + bool show_pfn;
> };
>
> #define PAGEMAP_WALK_SIZE (PMD_SIZE)
> @@ -1013,7 +1014,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
> struct page *page = NULL;
>
> if (pte_present(pte)) {
> - frame = pte_pfn(pte);
> + if (pm->show_pfn)
> + frame = pte_pfn(pte);
> flags |= PM_PRESENT;
> page = vm_normal_page(vma, addr, pte);
> if (pte_soft_dirty(pte))

Don't you need the same if (pm->show_pfn) check in is_swap_pte path, too?
(although I don't think that it can be exploited by row hammer attack ...)

Thanks,
Naoya Horiguchi