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

[Mark Williamson]

Reviewed-by: Mark Williamson <mwilliamson@xxxxxxxxxxxxxxxxx>

On Tue, Jul 21, 2015 at 9:39 AM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> wrote:
> On Tue, Jul 21, 2015 at 11:11 AM, Naoya Horiguchi
> <n-horiguchi@xxxxxxxxxxxxx> wrote:
>> 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@xxxxxxxxxxxxxx>
>>> 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@xxxxxxxxxxxxx
>>> ---
>>>  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 ...)
>
> Yeah, but I see no reason for that.
> Probably except swap on ramdrive, but this too weird =)
>
>>
>> Thanks,
>> Naoya Horiguchi
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