From: Greg KH <gregkh@linuxfoundation.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: stable@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com,
Song Liu <songliubraving@fb.com>, Adam Majer <amajer@suse.com>,
Dirk Mueller <dmueller@suse.com>, Takashi Iwai <tiwai@suse.de>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] mm/filemap: Fix handling of THPs in generic_file_buffered_read()
Date: Wed, 23 Feb 2022 18:44:16 +0100 [thread overview]
Message-ID: <YhZycDfxDo2K9Db+@kroah.com> (raw)
In-Reply-To: <20220223155918.927140-1-willy@infradead.org>
On Wed, Feb 23, 2022 at 03:59:18PM +0000, Matthew Wilcox (Oracle) wrote:
> When a THP is present in the page cache, we can return it several times,
> leading to userspace seeing the same data repeatedly if doing a read()
> that crosses a 64-page boundary. This is probably not a security issue
> (since the data all comes from the same file), but it can be interpreted
> as a transient data corruption issue. Fortunately, it is very rare as
> it can only occur when CONFIG_READ_ONLY_THP_FOR_FS is enabled, and it can
> only happen to executables. We don't often call read() on executables.
>
> This bug is fixed differently in v5.17 by commit 6b24ca4a1a8d
> ("mm: Use multi-index entries in the page cache"). That commit is
> unsuitable for backporting, so fix this in the clearest way. It
> sacrifices a little performance for clarity, but this should never
> be a performance path in these kernel versions.
>
> Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")
> Cc: stable@vger.kernel.org # v5.15, v5.16
> Link: https://lore.kernel.org/r/df3b5d1c-a36b-2c73-3e27-99e74983de3a@suse.cz/
> Analyzed-by: Adam Majer <amajer@suse.com>
> Analyzed-by: Dirk Mueller <dmueller@suse.com>
> Bisected-by: Takashi Iwai <tiwai@suse.de>
> Reported-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/filemap.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 82a17c35eb96..1293c3409e42 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2354,8 +2354,12 @@ static void filemap_get_read_batch(struct address_space *mapping,
> break;
> if (PageReadahead(head))
> break;
> - xas.xa_index = head->index + thp_nr_pages(head) - 1;
> - xas.xa_offset = (xas.xa_index >> xas.xa_shift) & XA_CHUNK_MASK;
> + if (PageHead(head)) {
> + xas_set(&xas, head->index + thp_nr_pages(head));
> + /* Handle wrap correctly */
> + if (xas.xa_index - 1 >= max)
> + break;
> + }
> continue;
> put_page:
> put_page(head);
> --
> 2.34.1
>
Now queued up, thanks!
greg k-h
prev parent reply other threads:[~2022-02-23 17:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-23 15:59 [PATCH] mm/filemap: Fix handling of THPs in generic_file_buffered_read() Matthew Wilcox (Oracle)
2022-02-23 17:05 ` Vlastimil Babka
2022-02-23 17:44 ` Greg KH [this message]
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