linux-kernel - Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4529b057-19ae-408b-8433-7d220f1871c0@lucifer.local>
Date:   Tue, 2 May 2023 13:52:17 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Matthew Wilcox <willy@...radead.org>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Leon Romanovsky <leon@...nel.org>,
        Christian Benvenuti <benve@...co.com>,
        Nelson Escobar <neescoba@...co.com>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Bjorn Topel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Richard Cochran <richardcochran@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Pavel Begunkov <asml.silence@...il.com>,
        Mika Penttila <mpenttil@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Theodore Ts'o <tytso@....edu>, Peter Xu <peterx@...hat.com>,
        Paul McKenney <paulmck@...nel.org>
Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing
 to file-backed mappings

On Tue, May 02, 2023 at 02:47:22PM +0200, David Hildenbrand wrote:
> On 02.05.23 14:40, Peter Zijlstra wrote:
> > On Tue, May 02, 2023 at 02:08:10PM +0200, Peter Zijlstra wrote:
> >
> > > > >
> > > > >
> > > > > 	if (folio_test_anon(folio))
> > > > > 		return true;
> > > >
> > > > This relies on the mapping so belongs below the lockdep assert imo.
> > >
> > > Oh, right you are.
> > >
> > > > >
> > > > > 	/*
> > > > > 	 * Having IRQs disabled (as per GUP-fast) also inhibits RCU
> > > > > 	 * grace periods from making progress, IOW. they imply
> > > > > 	 * rcu_read_lock().
> > > > > 	 */
> > > > > 	lockdep_assert_irqs_disabled();
> > > > >
> > > > > 	/*
> > > > > 	 * Inodes and thus address_space are RCU freed and thus safe to
> > > > > 	 * access at this point.
> > > > > 	 */
> > > > > 	mapping = folio_mapping(folio);
> > > > > 	if (mapping && shmem_mapping(mapping))
> > > > > 		return true;
> > > > >
> > > > > 	return false;
> > > > >
> > > > > > +}
> >
> > So arguably you should do *one* READ_ONCE() load of mapping and
> > consistently use that, this means open-coding both folio_test_anon() and
> > folio_mapping().
>
> Open-coding folio_test_anon() should not be required. We only care about
> PAGE_MAPPING_FLAGS stored alongside folio->mapping, that will stick around
> until the anon page was freed.
>

Ack, good point!

> @Lorenzo, you might also want to special-case hugetlb directly using
> folio_test_hugetlb().
>

I already am :) I guess you mean when I respin along these lines? Will port
that across to.

> --
> Thanks,
>
> David / dhildenb
>