From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C117C433F5 for ; Wed, 23 Feb 2022 17:44:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243444AbiBWRou (ORCPT ); Wed, 23 Feb 2022 12:44:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243436AbiBWRos (ORCPT ); Wed, 23 Feb 2022 12:44:48 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C369741331; Wed, 23 Feb 2022 09:44:19 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 608D6612B5; Wed, 23 Feb 2022 17:44:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B843C340EF; Wed, 23 Feb 2022 17:44:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1645638258; bh=ieSfUD0+w+fPqm2Dn3xrJaap6YZ7Coy/YY/N9ES6v70=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JAQR+4JUavxhFq+hS9+sZQ+fTnx8cWxy+hJe3MeOmKcAh1s0T0hBHHTxloDSCvmL8 MaegYED3lXb+3C0pzTUwT4XHQOrbqWAZCGXxf1kipuxtGej65WVPC3LQpMmH3tE2Db m2VDBXTn6Z1ATw5C0zDk5YPyPYNT5rPxre2wC/4g= Date: Wed, 23 Feb 2022 18:44:16 +0100 From: Greg KH To: "Matthew Wilcox (Oracle)" Cc: stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, Song Liu , Adam Majer , Dirk Mueller , Takashi Iwai , Vlastimil Babka Subject: Re: [PATCH] mm/filemap: Fix handling of THPs in generic_file_buffered_read() Message-ID: References: <20220223155918.927140-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220223155918.927140-1-willy@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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 > Analyzed-by: Dirk Mueller > Bisected-by: Takashi Iwai > Reported-by: Vlastimil Babka > Signed-off-by: Matthew Wilcox (Oracle) > --- > 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