linux-kernel - Re: [RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps

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Date:	Mon, 13 Jun 2016 13:43:13 -0700
From:	Kees Cook <kees@...flux.net>
To:	Topi Miettinen <toiwoton@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps

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@...il.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.

-Kees

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

-- 
Kees Cook                                            @outflux.net