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:

quoted

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"