Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

From: Matthew Wilcox
Date: Wed Jan 16 2019 - 16:37:19 EST

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

> 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

> 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