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Date: Wed, 11 Apr 2018 08:56:58 +0800 From: "Huang\, Ying" <ying.huang@...el.com> To: "Kirill A. Shutemov" <kirill@...temov.name> Cc: Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andrei Vagin <avagin@...nvz.org>, Dan Williams <dan.j.williams@...el.com>, Jerome Glisse <jglisse@...hat.com>, Daniel Colascione <dancol@...gle.com>, Zi Yan <zi.yan@...rutgers.edu>, Naoya Horiguchi <n-horiguchi@...jp.nec.com> Subject: Re: [PATCH -mm] mm, pagemap: Fix swap offset value for PMD migration entry "Kirill A. Shutemov" <kirill@...temov.name> writes: > 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@...ux.intel.com> >> AuthorDate: Mon Mar 9 23:11:12 2015 +0200 >> Commit: Linus Torvalds <torvalds@...ux-foundation.org> >> 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. So you think we should hide all swap entry information if (!pm->show_pfn) regardless they are migration swap entries or not? Best Regards, Huang, Ying
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