On Tue, Apr 10, 2018 at 08:57:19AM +0800, Huang, Ying wrote: > >> the swap offset reported doesn't > >> reflect this. And in the loop to report information of each sub-page, > >> the swap offset isn't increased accordingly as that for PFN. > >> > >> BTW: migration swap entries have PFN information, do we need to > >> restrict whether to show them? > > > > For what reason? Address obfuscation? > > This is an existing feature for PFN report of /proc/<pid>/pagemap, > reason is in following commit log. I am wondering whether that is > necessary for migration swap entries too. > > ab676b7d6fbf4b294bf198fb27ade5b0e865c7ce > Author: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > AuthorDate: Mon Mar 9 23:11:12 2015 +0200 > Commit: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > CommitDate: Tue Mar 17 09:31:30 2015 -0700 > > pagemap: do not leak physical addresses to non-privileged userspace > > As pointed by recent post[1] on exploiting DRAM physical imperfection, > /proc/PID/pagemap exposes sensitive information which can be used to do > attacks. > > This disallows anybody without CAP_SYS_ADMIN to read the pagemap. > > [1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html > > [ Eventually we might want to do anything more finegrained, but for now > this is the simple model. - Linus ] Note that there's follow up to the commit: 1c90308e7a77 ("pagemap: hide physical addresses from non-privileged users") It introduces pm->show_pfn and it should be applied to swap entries too. -- Kirill A. Shutemov
