Messages in this thread | | | Subject | Re: [PATCH] mm: dump_page: add debugfs file for dumping page state by pfn | From | Konstantin Khlebnikov <> | Date | Mon, 25 May 2020 19:05:08 +0300 |
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On 25/05/2020 19.03, Konstantin Khlebnikov wrote: > > > On 25/05/2020 18.33, Matthew Wilcox wrote: >> On Mon, May 25, 2020 at 05:19:11PM +0300, Konstantin Khlebnikov wrote: >>> Tool 'page-types' could list pages mapped by process or file cache pages, >>> but it shows only limited amount of state exported via procfs. >>> >>> Let's employ existing helper dump_page() to reach remaining information: >>> writing pfn into /sys/kernel/debug/dump_page dumps state into kernel log. >>> >>> # echo 0x37c43c > /sys/kernel/debug/dump_page >>> # dmesg | tail -6 >>> page:ffffcb0b0df10f00 refcount:1 mapcount:0 mapping:000000007755d3d9 index:0x30 >>> 0xffffffffae4239e0 name:"libGeoIP.so.1.6.9" >>> flags: 0x200000000020014(uptodate|lru|mappedtodisk) >>> raw: 0200000000020014 ffffcb0b187fd288 ffffcb0b189e6248 ffff9528a04afe10 >>> raw: 0000000000000030 0000000000000000 00000001ffffffff 0000000000000000 >>> page dumped because: debugfs request >> >> This makes me deeply uncomfortable. We're using %px, and %lx >> (for the 'raw' lines) so we actually get to see kernel addresses. >> We've rationalised this in the past as being acceptable because you're >> already in an "assert triggered" kind of situation. Now you're adding >> a way for any process with CAP_SYS_ADMIN to get kernel addresses dumped >> into the syslog. >> >> I think we need a different function for this, or we need to re-audit >> dump_page() for exposing kernel pointers, and not expose the raw data >> in struct page. >> > > It's better to add switch for disabling paranoia if bad things happening. > I.e. keep everything safe by default (or whatever sysctl/config set) and > flip the switch when needed.
Also I'm ok to seal this interface if kernel in mode of serious paranoia.
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