Andrew Morton <[email protected]> writes: > On Sun, 8 Apr 2018 11:37:37 +0800 "Huang, Ying" <[email protected]> wrote: > >> From: Huang Ying <[email protected]> >> >> The swap offset reported by /proc/<pid>/pagemap may be not correct for >> PMD migration entry. If addr passed into pagemap_range() isn't > > pagemap_pmd_range(), yes?
Yes. Sorry for typo. >> aligned with PMD start address, > > How can this situation come about? After open /proc/<pid>/pagemap, if user seeks to a page whose address doesn't aligned with PMD start address. I have verified this with a simple test program. >> 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 <[email protected]> AuthorDate: Mon Mar 9 23:11:12 2015 +0200 Commit: Linus Torvalds <[email protected]> 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 ] Signed-off-by: Kirill A. Shutemov <[email protected]> Acked-by: Konstantin Khlebnikov <[email protected]> Acked-by: Andy Lutomirski <[email protected]> Cc: Pavel Emelyanov <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Mark Seaborn <[email protected]> Cc: [email protected] Signed-off-by: Linus Torvalds <[email protected]> Best Regards, Huang, Ying
