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Date:   Wed, 9 Jan 2019 03:31:35 +0100 (CET)
From:   Jiri Kosina <jikos@kernel.org>
To:     Dave Chinner <david@fromorbit.com>
cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jann Horn <jannh@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Michal Hocko <mhocko@suse.com>, Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged
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On Wed, 9 Jan 2019, Dave Chinner wrote:

> > But mincore is certainly the easiest interface, and the one that
> > doesn't require much effort or setup.
> 
> Off the top of my head, here's a few vectors for reading the page
> cache residency state without perturbing the page cache residency
> pattern:
> 	- mincore
> 	- preadv2(RWF_NOWAIT)
> 	- fadvise(POSIX_FADV_RANDOM); timed read(2) syscalls
> 	- madvise(MADV_RANDOM); timed read of first byte in each page

While I obviously agree that all those are creating pagecache sidechannel 
in principle, I think we really should mostly focus on the first two (with 
mincore() already having been covered).

Rationale has been provided by Daniel Gruss in this thread -- if the 
attacker is left with cache timing as the only available vector, he's 
going to be much more successful with mounting hardware cache timing 
attack anyway.

Thanks,

-- 
Jiri Kosina
SUSE Labs