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Wed, 18 Mar 2026 22:34:52 -0700 (PDT) Received: from aegis.localdomain ([49.148.247.44]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b06e441374sm44983075ad.29.2026.03.18.22.34.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 22:34:52 -0700 (PDT) From: Daniel J Blueman To: Chris Mason , David Sterba , Qu Wenruo Cc: Daniel J Blueman , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] btrfs: Fix BTRFS arm64 tagged KASAN false-positive Date: Thu, 19 Mar 2026 13:34:10 +0800 Message-ID: <20260319053413.14771-1-daniel@quora.org> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When booting Linux 7.0-rc4 on a Qualcomm Snapdragon X1 with KASAN software tagging with a BTRFS filesystem, we see: BUG: KASAN: invalid-access in xxh64_update (lib/xxhash.c:143 lib/xxhash.c:2= 83) Read of size 8 at addr 7bff000804fe1000 by task kworker/u49:2/138 Pointer tag: [7b], memory tag: [b2] CPU: 0 UID: 0 PID: 138 Comm: kworker/u49:2 Not tainted 7.0.0-rc4+ #34 PREEM= PTLAZY Hardware name: LENOVO 83ED/LNVNB161216, BIOS NHCN60WW 09/11/2025 Workqueue: btrfs-endio-meta simple_end_io_work Call trace: show_stack (arch/arm64/kernel/stacktrace.c:501) (C) dump_stack_lvl (lib/dump_stack.c:122) print_report (mm/kasan/report.c:379 mm/kasan/report.c:482) kasan_report (mm/kasan/report.c:597) kasan_check_range (mm/kasan/sw_tags.c:86 (discriminator 1)) __hwasan_loadN_noabort (mm/kasan/sw_tags.c:158) xxh64_update (lib/xxhash.c:143 lib/xxhash.c:283) btrfs_csum_update (fs/btrfs/fs.c:106) csum_tree_block (fs/btrfs/disk-io.c:103 (discriminator 3)) btrfs_validate_extent_buffer (fs/btrfs/disk-io.c:389) end_bbio_meta_read (fs/btrfs/extent_io.c:3853 (discriminator 1)) btrfs_bio_end_io (fs/btrfs/bio.c:152) simple_end_io_work (fs/btrfs/bio.c:388) process_one_work (./arch/arm64/include/asm/jump_label.h:36 ./include/trace/= events/workqueue.h:110 kernel/workqueue.c:3281) worker_thread (kernel/workqueue.c:3353 (discriminator 2) kernel/workqueue.c= :3440 (discriminator 2)) kthread (kernel/kthread.c:436) ret_from_fork (arch/arm64/kernel/entry.S:861) The buggy address belongs to the physical page: page: refcount:3 mapcount:0 mapping:f1ff00080055dee8 index:0x2467bd pfn:0x8= 84fe1 memcg:51ff000800e68ec0 aops:btree_aops ino:1 flags: 0x9340000000004000(private|zone=3D2|kasantag=3D0x4d) raw: 9340000000004000 0000000000000000 dead000000000122 f1ff00080055dee8 raw: 00000000002467bd 43ff00081d0cc6f0 00000003ffffffff 51ff000800e68ec0 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff000804fe0e00: 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b ffff000804fe0f00: 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b >ffff000804fe1000: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 ^ ffff000804fe1100: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 ffff000804fe1200: b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 b2 This occurs as contiguous pages may have different KASAN tags in the upper = address bits, leading to a tag mismatch if linear addressing is used. Fix this by treating them as discontiguous. Signed-off-by: Daniel J Blueman Fixes: 397239ed6a6c ("btrfs: allow extent buffer helpers to skip cross-page= handling") --- fs/btrfs/extent_io.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 5f97a3d2a8d7..e2b241fb6c0e 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3517,8 +3517,16 @@ struct extent_buffer *alloc_extent_buffer(struct btr= fs_fs_info *fs_info, * At this stage, either we allocated a large folio, thus @i * would only be 0, or we fall back to per-page allocation. */ - if (i && folio_page(eb->folios[i - 1], 0) + 1 !=3D folio_page(folio, 0)) - page_contig =3D false; + if (i > 0) { + struct page *prev =3D folio_page(eb->folios[i - 1], 0); + struct page *curr =3D folio_page(folio, 0); + + /* + * Contiguous pages may have different tags; can't be treated as contig= uous + */ + if (curr !=3D prev + 1 || page_kasan_tag(curr) !=3D page_kasan_tag(prev= )) + page_contig =3D false; + } =20 if (!btrfs_meta_folio_test_uptodate(folio, eb)) uptodate =3D 0; --=20 2.53.0