From: Vlastimil Babka <vbabka@suse.cz>
To: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
Jann Horn <jannh@google.com>, Michal Hocko <mhocko@kernel.org>,
Nadav Amit <namit@vmware.com>, Rik van Riel <riel@surriel.com>,
Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Peter Xu <peterx@redhat.com>, Donald Dutile <ddutile@redhat.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Jan Kara <jack@suse.cz>, Liang Zhang <zhangliang5@huawei.com>,
linux-mm@kvack.org
Subject: Re: [PATCH v3 4/9] mm: streamline COW logic in do_swap_page()
Date: Thu, 10 Mar 2022 10:41:36 +0100 [thread overview]
Message-ID: <5b108bbb-0ddc-0f46-1b4b-6ceaa95727f2@suse.cz> (raw)
In-Reply-To: <20220131162940.210846-5-david@redhat.com>
On 1/31/22 17:29, David Hildenbrand wrote:
> Currently we have a different COW logic when:
> * triggering a read-fault to swapin first and then trigger a write-fault
> -> do_swap_page() + do_wp_page()
> * triggering a write-fault to swapin
> -> do_swap_page() + do_wp_page() only if we fail reuse in do_swap_page()
>
> The COW logic in do_swap_page() is different than our reuse logic in
> do_wp_page(). The COW logic in do_wp_page() -- page_count() == 1 -- makes
> currently sure that we certainly don't have a remaining reference, e.g.,
> via GUP, on the target page we want to reuse: if there is any unexpected
> reference, we have to copy to avoid information leaks.
>
> As do_swap_page() behaves differently, in environments with swap enabled we
> can currently have an unintended information leak from the parent to the
> child, similar as known from CVE-2020-29374:
>
> 1. Parent writes to anonymous page
> -> Page is mapped writable and modified
> 2. Page is swapped out
> -> Page is unmapped and replaced by swap entry
> 3. fork()
> -> Swap entries are copied to child
> 4. Child pins page R/O
> -> Page is mapped R/O into child
> 5. Child unmaps page
> -> Child still holds GUP reference
> 6. Parent writes to page
> -> Page is reused in do_swap_page()
> -> Child can observe changes
>
> Exchanging 2. and 3. should have the same effect.
>
> Let's apply the same COW logic as in do_wp_page(), conditionally trying to
> remove the page from the swapcache after freeing the swap entry, however,
> before actually mapping our page. We can change the order now that
> we use try_to_free_swap(), which doesn't care about the mapcount,
> instead of reuse_swap_page().
>
> To handle references from the LRU pagevecs, conditionally drain the local
> LRU pagevecs when required, however, don't consider the page_count() when
> deciding whether to drain to keep it simple for now.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
next prev parent reply other threads:[~2022-03-10 9:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 16:29 [PATCH v3 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap David Hildenbrand
2022-01-31 16:29 ` [PATCH v3 1/9] mm: optimize do_wp_page() for exclusive pages in the swapcache David Hildenbrand
2022-01-31 16:29 ` [PATCH v3 2/9] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs David Hildenbrand
2022-03-09 17:53 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 3/9] mm: slightly clarify KSM logic in do_swap_page() David Hildenbrand
2022-03-09 18:03 ` Vlastimil Babka
2022-03-09 18:48 ` Yang Shi
2022-03-09 19:15 ` David Hildenbrand
2022-03-09 20:50 ` Andrew Morton
2022-01-31 16:29 ` [PATCH v3 4/9] mm: streamline COW " David Hildenbrand
2022-03-10 9:41 ` Vlastimil Babka [this message]
2022-01-31 16:29 ` [PATCH v3 5/9] mm/huge_memory: streamline COW logic in do_huge_pmd_wp_page() David Hildenbrand
2022-03-10 9:52 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 6/9] mm/khugepaged: remove reuse_swap_page() usage David Hildenbrand
2022-02-01 21:31 ` Yang Shi
2022-03-10 10:37 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 7/9] mm/swapfile: remove stale reuse_swap_page() David Hildenbrand
2022-02-02 14:35 ` Christoph Hellwig
2022-02-02 17:01 ` David Hildenbrand
2022-03-10 10:44 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 8/9] mm/huge_memory: remove stale page_trans_huge_mapcount() David Hildenbrand
2022-03-10 10:50 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 9/9] mm/huge_memory: remove stale locking logic from __split_huge_pmd() David Hildenbrand
2022-03-10 11:02 ` Vlastimil Babka
2022-02-01 18:59 ` [PATCH v3 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap Linus Torvalds
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 \
--in-reply-to=5b108bbb-0ddc-0f46-1b4b-6ceaa95727f2@suse.cz \
--to=vbabka@suse.cz \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=david@redhat.com \
--cc=ddutile@redhat.com \
--cc=guro@fb.com \
--cc=hch@lst.de \
--cc=hughd@google.com \
--cc=jack@suse.cz \
--cc=jannh@google.com \
--cc=jgg@nvidia.com \
--cc=jhubbard@nvidia.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=mike.kravetz@oracle.com \
--cc=namit@vmware.com \
--cc=oleg@redhat.com \
--cc=peterx@redhat.com \
--cc=riel@surriel.com \
--cc=rientjes@google.com \
--cc=rppt@linux.ibm.com \
--cc=shakeelb@google.com \
--cc=shy828301@gmail.com \
--cc=torvalds@linux-foundation.org \
--cc=willy@infradead.org \
--cc=zhangliang5@huawei.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).