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Date: Wed, 16 Jan 2019 04:36:07 -0800
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged
Message-ID: <20190116123607.GG6310@bombadil.infradead.org>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Snyder <joshs@netflix.com>, Dominique Martinet <asmadeus@codewreck.org>, Dave Chinner <david@fromorbit.com>, Jiri Kosina <jikos@kernel.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>

On Wed, Jan 16, 2019 at 05:00:25PM +1200, Linus Torvalds wrote:
> And if you're not the owner of the file, do you have another
> suggestion for that "Yes, I have the right to see what's in-core for
> this file". Because the problem is literally that if it's some random
> read-only system file, the kernel shouldn't leak access patterns to
> it..

This probably isn't a good heuristic, but thought I'd mention it
anyway ...  if the file is executable and you're not the owner, mincore
always/never says its pages are resident.  That'd fix all library leaks,
but then there's probably a smart way of figuring out something from
access patterns to a data file of some kind (/etc/passwd?)