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Date: Wed, 16 Jan 2019 13:37:08 -0800
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged
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To: Jiri Kosina <jikos@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Dominique Martinet <asmadeus@codewreck.org>, Andy Lutomirski <luto@amacapital.net>, Josh Snyder <joshs@netflix.com>, Dave Chinner <david@fromorbit.com>, 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 09:23:04PM +0100, Jiri Kosina wrote:
> On Thu, 17 Jan 2019, Linus Torvalds wrote:
> > As I suggested earlier in the thread, the fix for RWF_NOWAIT might be
> > to just move the test down to after readahead.

Your patch 3/3 just removes the test.  Am I right in thinking that it
doesn't need to be *moved* because the existing test after !PageUptodate
catches it?

Of course, there aren't any tests for RWF_NOWAIT in xfstests.  Are there
any in LTP?

Some typos in the commit messages:

> Another aproach (checking file access permissions in order to decide
"approach"

> Subject: [PATCH 2/3] mm/mincore: make mincore() more conservative
> 
> The semantics of what mincore() considers to be resident is not completely
> clearar, but Linux has always (since 2.3.52, which is when mincore() was
"clear"

> initially done) treated it as "page is available in page cache".
> 
> That's potentially a problem, as that [in]directly exposes meta-information
> about pagecache / memory mapping state even about memory not strictly belonging
> to the process executing the syscall, opening possibilities for sidechannel
> attacks.
> 
> Change the semantics of mincore() so that it only reveals pagecache information
> for non-anonymous mappings that belog to files that the calling process could
"belong"