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Subject: Re: [RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps
To: Kees Cook <kees@outflux.net>
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Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Jerome Marchand <jmarchan@redhat.com>,
        Laurent Dufour <ldufour@linux.vnet.ibm.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>
From: Topi Miettinen <toiwoton@gmail.com>
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Date: Mon, 13 Jun 2016 20:52:22 +0000
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On 06/13/16 20:43, Kees Cook wrote:
> On Mon, Jun 13, 2016 at 10:44:25PM +0300, Topi Miettinen wrote:
>> Add a flag to /proc/self/maps to show that the memory area is locked.
>>
>> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
>> ---
>>  fs/proc/task_mmu.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index 4648c7f..8229509 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
> 
> If you change the maps format, you'll need to update task_nommu.c too.
> 
>> @@ -313,13 +313,14 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
>>  		end -= PAGE_SIZE;
>>  
>>  	seq_setwidth(m, 25 + sizeof(void *) * 6 - 1);
> 
> I think the width needs to be adjusted for the new character.
> 
>> -	seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
>> +	seq_printf(m, "%08lx-%08lx %c%c%c%c%c %08llx %02x:%02x %lu ",
> 
> Have you checked that no userspace tools that parse "maps" will break with
> this flag addition?
> 
>>  			start,
>>  			end,
>>  			flags & VM_READ ? 'r' : '-',
>>  			flags & VM_WRITE ? 'w' : '-',
>>  			flags & VM_EXEC ? 'x' : '-',
>>  			flags & VM_MAYSHARE ? 's' : 'p',
>> +			flags & VM_LOCKED ? 'l' : '-',
> 
> IIUC, the smaps file already includes the locked information in VmFlags as
> "lo" (see show_smap_vma_flags), so I think you probably don't want this
> patch at all.

Yes. the amount of locked memory is also shown:
Locked:                8 kB
VmFlags: rd wr mr mw me lo ac sd

Sorry, I didn't notice that. I'll drop the patch.

-Topi

> 
> -Kees
> 
>>  			pgoff,
>>  			MAJOR(dev), MINOR(dev), ino);
>>  
>> -- 
>> 2.8.1
>