From: Dave Hansen <firstname.lastname@example.org> To: Minchan Kim <email@example.com>, Michal Hocko <firstname.lastname@example.org> Cc: Jann Horn <email@example.com>, Linux-MM <firstname.lastname@example.org>, kernel list <email@example.com>, Daniel Colascione <firstname.lastname@example.org>, "Joel Fernandes (Google)" <email@example.com>, Andrew Morton <firstname.lastname@example.org> Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings? Date: Thu, 12 Mar 2020 13:26:16 -0700 Message-ID: <email@example.com> (raw) In-Reply-To: <20200312201602.GA68817@google.com> On 3/12/20 1:16 PM, Minchan Kim wrote: > On Thu, Mar 12, 2020 at 09:22:48AM +0100, Michal Hocko wrote: > I't likde to wait Jann's reply since Dave gave his opinion about the vulnerability. > https://firstname.lastname@example.org/ > Jann, could you give your insigh about that practically it's possible? FWIW, just checking for mapcount>=1 seems like a pretty sane fix to me. I went looking at doing it another way, but Michal was quite correct. We'd probably end up having to special-case something underneath shrink_page_list(). > A real dumb question to understand vulnerability: > > The attacker would be able to trigger heavy memory consumption so that he > could make paging them out without MADV_PAGEOUT. I know MADV_PAGEOUT makes > it easier but he still could do without MADV_PAGEOUT. > What makes difference here? Causing memory pressure is quite a bit more disruptive than MADV_PAGEOUT. It's a much more blunt instrument and is likely to result in a lot of collateral damage and a lot of I/O. MADV_PAGEOUT is *surgical*. You can target one very specific page if, for instance, you think that your victim is reading it in a way that is vulnerable. You can also do it with zero I/O (after the initial pageout). > To clarify how MADV_PAGEWORK works: > If other process has accessed the page so that his page table has access > bit marked, MADV_PAGEOUT couldn't page it out. The attacker doesn't need to get the victim to get a major fault, it just needs to induce *a* fault. I actually did an experiment to see how this would work in practice. 1. Allocate some memory(), touch it 2. fork() 3. In the parent: Loop reading the memory 4. In the child: loop running MADV_PAGEOUT The pages stayed in the swap cache and the parent reading the memory saw a constant stream of faults.
next prev parent reply index Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-10 18:08 Jann Horn 2020-03-10 18:48 ` Michal Hocko 2020-03-10 19:11 ` Jann Horn 2020-03-10 21:09 ` Michal Hocko 2020-03-10 22:48 ` Dave Hansen 2020-03-11 8:45 ` Michal Hocko 2020-03-11 22:02 ` Minchan Kim 2020-03-11 23:53 ` Shakeel Butt 2020-03-12 0:18 ` Minchan Kim 2020-03-12 2:03 ` Daniel Colascione 2020-03-12 15:15 ` Shakeel Butt 2020-03-10 20:19 ` Daniel Colascione 2020-03-10 21:40 ` Jann Horn 2020-03-10 21:52 ` Daniel Colascione 2020-03-10 22:14 ` Minchan Kim 2020-03-12 8:22 ` Michal Hocko 2020-03-12 15:40 ` Vlastimil Babka 2020-03-12 20:16 ` Minchan Kim 2020-03-12 20:26 ` Dave Hansen [this message] 2020-03-12 20:41 ` Michal Hocko 2020-03-13 2:08 ` Minchan Kim 2020-03-13 8:05 ` Michal Hocko 2020-03-13 20:59 ` Minchan Kim 2020-03-16 9:20 ` Michal Hocko 2020-03-17 1:43 ` Minchan Kim 2020-03-17 7:12 ` Michal Hocko 2020-03-17 15:00 ` Minchan Kim 2020-03-17 15:58 ` Michal Hocko 2020-03-17 17:20 ` Minchan Kim 2020-03-12 21:41 ` Dave Hansen 2020-03-13 2:00 ` Minchan Kim 2020-03-13 16:59 ` Dave Hansen 2020-03-13 21:13 ` Minchan Kim 2020-03-12 23:29 ` Jann Horn
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-mm Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \ email@example.com public-inbox-index linux-mm Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kvack.linux-mm AGPL code for this site: git clone https://public-inbox.org/public-inbox.git