Re: [PATCH 3/3] mm/mincore: provide mapped status when cached status is not allowed

From: Vlastimil Babka
Date: Fri Feb 01 2019 - 04:27:43 EST

On 2/1/19 10:11 AM, Michal Hocko wrote:
> On Fri 01-02-19 10:04:23, Vlastimil Babka wrote:
>> The side channel exists anyway as long as process can e.g. check if
>> its rss shrinked, and I doubt we are going to remove that possibility.
> Well, but rss update will not tell you that the page has been faulted in
> which is the most interesting part.

Sure, but the patch doesn't add back that capability neither. It allows
to recognize page being reclaimed, and I argue you can infer that from
rss change as well. That change is mentioned in the last paragraph in
changelog, and I thought "add a hard to evaluate side channel" in your
reply referred to that. It doesn't add back the "original" side channel
to detect somebody else accessed a page.

> You shouldn't be able to sniff on
> /proc/$vicimt/smaps as an attacker.