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

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Date:	Tue, 21 Jul 2015 11:39:56 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Mark Williamson <mwilliamson@...o-software.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v4 4/5] pagemap: hide physical addresses from
 non-privileged users

On Tue, Jul 21, 2015 at 11:11 AM, Naoya Horiguchi
<n-horiguchi@...jp.nec.com> 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@...dex-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 ...)

Yeah, but I see no reason for that.
Probably except swap on ramdrive, but this too weird =)

>
> Thanks,
> Naoya Horiguchi
> --
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