Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Sun, 8 Apr 2018 11:37:37 +0800 "Huang, Ying" <ying.huang@xxxxxxxxx> wrote: > >> From: Huang Ying <ying.huang@xxxxxxxxx> >> >> 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 <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 ] Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Mark Seaborn <mseaborn@xxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Best Regards, Huang, Ying
