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Date: Mon, 13 Jun 2016 13:43:13 -0700
From: Kees Cook <kees@outflux.net>
To: Topi Miettinen <toiwoton@gmail.com>
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>
Subject: Re: [RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps
Message-ID: <20160613204312.GP3346@outflux.net>
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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.

-Kees

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

-- 
Kees Cook                                            @outflux.net