linux-kernel - Re: [PATCH] mm/mincore: allow for making sys

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Message-ID: <20190116213708.GN6310@bombadil.infradead.org>
Date:   Wed, 16 Jan 2019 13:37:08 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Snyder <joshs@...flix.com>,
        Dave Chinner <david@...morbit.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

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"