lwn.git/fs/erofs/decompressor.c, branch v6.9-rc4

erofs: fix uninitialized page cache reported by KMSAN

2024-03-07T02:21:00+00:00

syzbot reports a KMSAN reproducer [1] which generates a crafted filesystem image and causes IMA to read uninitialized page cache. Later, (rq->outputsize > rq->inputsize) will be formally supported after either large uncompressed pclusters (> block size) or big lclusters are landed. However, currently there is no way to generate such filesystems by using mkfs.erofs. Thus, let's mark this condition as unsupported for now. [1] https://lore.kernel.org/r/0000000000002be12a0611ca7ff8@google.com Reported-and-tested-by: syzbot+7bc44a489f0ef0670bd5@syzkaller.appspotmail.com Fixes: 1ca01520148a ("erofs: refine z_erofs_transform_plain() for sub-page block support") Reviewed-by: Sandeep Dhavale Reviewed-by: Yue Hu Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20240304035339.425857-1-hsiangkao@linux.alibaba.com

erofs: relaxed temporary buffers allocation on readahead

2024-01-27T04:28:08+00:00

Even with inplace decompression, sometimes very few temporary buffers may be still needed for a single decompression shot (e.g. 16 pages for 64k sliding window or 4 pages for 16k sliding window). In low-memory scenarios, it would be better to try to allocate with GFP_NOWAIT on readahead first. That can help reduce the time spent on page allocation under durative memory pressure. Here are detailed performance numbers under multi-app launch benchmark workload [1] on ARM64 Android devices (8-core CPU and 8GB of memory) running a 5.15 LTS kernel with EROFS of 4k pclusters: +----------------------------------------------+ | LZ4 | vanilla | patched | diff | |----------------+---------+---------+---------| | Average (ms) | 3364 | 2684 | -20.21% | [64k sliding window] |----------------+---------+---------+---------| | Average (ms) | 2079 | 1610 | -22.56% | [16k sliding window] +----------------------------------------------+ The total size of system images for 4k pclusters is almost unchanged: (64k sliding window) 9,117,044 KB (16k sliding window) 9,113,096 KB Therefore, in addition to switch the sliding window from 64k to 16k, after applying this patch, it can eventually save 52.14% (3364 -> 1610) on average with no memory reservation. That is particularly useful for embedded devices with limited resources. [1] https://lore.kernel.org/r/20240109074143.4138783-1-guochunhai@vivo.com Suggested-by: Gao Xiang Signed-off-by: Chunhai Guo Signed-off-by: Gao Xiang Reviewed-by: Yue Hu Link: https://lore.kernel.org/r/20240126140142.201718-1-hsiangkao@linux.alibaba.com

Merge tag 'erofs-for-6.8-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

2024-01-19T02:12:26+00:00

Pull erofs fixes from Gao Xiang: - Fix a "BUG: kernel NULL pointer dereference" issue due to inconsistent on-disk indices of compressed inodes against per-sb `available_compr_algs` generated by Syzkaller - Don't use certain unnecessary folio_*() helpers if the folio type (page cache) is known * tag 'erofs-for-6.8-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs: erofs: Don't use certain unnecessary folio_*() functions erofs: fix inconsistent per-file compression format

erofs: fix inconsistent per-file compression format

2024-01-13T15:58:08+00:00

EROFS can select compression algorithms on a per-file basis, and each per-file compression algorithm needs to be marked in the on-disk superblock for initialization. However, syzkaller can generate inconsistent crafted images that use an unsupported algorithmtype for specific inodes, e.g. use MicroLZMA algorithmtype even it's not set in `sbi->available_compr_algs`. This can lead to an unexpected "BUG: kernel NULL pointer dereference" if the corresponding decompressor isn't built-in. Fix this by checking against `sbi->available_compr_algs` for each m_algorithmformat request. Incorrect !erofs_sb_has_compr_cfgs preset bitmap is now fixed together since it was harmless previously. Reported-by: Fixes: 8f89926290c4 ("erofs: get compression algorithms directly on mapping") Fixes: 622ceaddb764 ("erofs: lzma compression support") Reviewed-by: Yue Hu Link: https://lore.kernel.org/r/20240113150602.1471050-1-hsiangkao@linux.alibaba.com Signed-off-by: Gao Xiang

erofs: avoid debugging output for (de)compressed data

2024-01-10T11:59:39+00:00

Syzbot reported a KMSAN warning, erofs: (device loop0): z_erofs_lz4_decompress_mem: failed to decompress -12 in[46, 4050] out[917] ===================================================== BUG: KMSAN: uninit-value in hex_dump_to_buffer+0xae9/0x10f0 lib/hexdump.c:194 .. print_hex_dump+0x13d/0x3e0 lib/hexdump.c:276 z_erofs_lz4_decompress_mem fs/erofs/decompressor.c:252 [inline] z_erofs_lz4_decompress+0x257e/0x2a70 fs/erofs/decompressor.c:311 z_erofs_decompress_pcluster fs/erofs/zdata.c:1290 [inline] z_erofs_decompress_queue+0x338c/0x6460 fs/erofs/zdata.c:1372 z_erofs_runqueue+0x36cd/0x3830 z_erofs_read_folio+0x435/0x810 fs/erofs/zdata.c:1843 The root cause is that the printed decompressed buffer may be filled incompletely due to decompression failure. Since they were once only used for debugging, get rid of them now. Reported-and-tested-by: syzbot+6c746eea496f34b3161d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/000000000000321c24060d7cfa1c@google.com Reviewed-by: Yue Hu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231227151903.2900413-1-hsiangkao@linux.alibaba.com

erofs: refine z_erofs_transform_plain() for sub-page block support

2023-12-18T07:49:39+00:00

Sub-page block support is still unusable even with previous commits if interlaced PLAIN pclusters exist. Such pclusters can be found if the fragment feature is enabled. This commit tries to handle "the head part" of interlaced PLAIN pclusters first: it was once explained in commit fdffc091e6f9 ("erofs: support interlaced uncompressed data for compressed files"). It uses a unique way for both shifted and interlaced PLAIN pclusters. As an added bonus, PLAIN pclusters larger than the block size is also supported now for the upcoming large lclusters. Reviewed-by: Yue Hu Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231206091057.87027-5-hsiangkao@linux.alibaba.com

erofs: fix lz4 inplace decompression

2023-12-14T16:22:16+00:00

Currently EROFS can map another compressed buffer for inplace decompression, that was used to handle the cases that some pages of compressed data are actually not in-place I/O. However, like most simple LZ77 algorithms, LZ4 expects the compressed data is arranged at the end of the decompressed buffer and it explicitly uses memmove() to handle overlapping: __________________________________________________________ |_ direction of decompression --> ____ |_ compressed data _| Although EROFS arranges compressed data like this, it typically maps two individual virtual buffers so the relative order is uncertain. Previously, it was hardly observed since LZ4 only uses memmove() for short overlapped literals and x86/arm64 memmove implementations seem to completely cover it up and they don't have this issue. Juhyung reported that EROFS data corruption can be found on a new Intel x86 processor. After some analysis, it seems that recent x86 processors with the new FSRM feature expose this issue with "rep movsb". Let's strictly use the decompressed buffer for lz4 inplace decompression for now. Later, as an useful improvement, we could try to tie up these two buffers together in the correct order. Reported-and-tested-by: Juhyung Park Closes: https://lore.kernel.org/r/CAD14+f2AVKf8Fa2OO1aAUdDNTDsVzzR6ctU_oJSmTyd6zSYR2Q@mail.gmail.com Fixes: 0ffd71bcc3a0 ("staging: erofs: introduce LZ4 decompression inplace") Fixes: 598162d05080 ("erofs: support decompress big pcluster for lz4 backend") Cc: stable # 5.4+ Tested-by: Yifan Zhao Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231206045534.3920847-1-hsiangkao@linux.alibaba.com

erofs: tidy up redundant includes

2023-10-30T22:58:49+00:00

- Remove unused includes like and ; - Move common includes into "internal.h". Signed-off-by: Ferry Meng Reviewed-by: Gao Xiang Reviewed-by: Yue Hu Reviewed-by: Chao Yu Link: https://lore.kernel.org/r/20231026021627.23284-2-mengferry@linux.alibaba.com Signed-off-by: Gao Xiang

erofs: simplify compression configuration parser

2023-10-30T22:57:19+00:00

Move erofs_load_compr_cfgs() into decompressor.c as well as introduce a callback instead of a hard-coded switch for each algorithm for simplicity. Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231022130957.11398-1-xiang@kernel.org

erofs: DEFLATE compression support

2023-08-11T04:11:17+00:00

Add DEFLATE compression as the 3rd supported algorithm. DEFLATE is a popular generic-purpose compression algorithm for quite long time (many advanced formats like gzip, zlib, zip, png are all based on that) as Apple documentation written "If you require interoperability with non-Apple devices, use COMPRESSION_ZLIB. [1]". Due to its popularity, there are several hardware on-market DEFLATE accelerators, such as (s390) DFLTCC, (Intel) IAA/QAT, (HiSilicon) ZIP accelerator, etc. In addition, there are also several high-performence IP cores and even open-source FPGA approches available for DEFLATE. Therefore, it's useful to support DEFLATE compression in order to find a way to utilize these accelerators for asynchronous I/Os and get benefits from these later. Besides, it's a good choice to trade off between compression ratios and performance compared to LZ4 and LZMA. The DEFLATE core format is simple as well as easy to understand, therefore the code size of its decompressor is small even for the bootloader use cases. The runtime memory consumption is quite limited too (e.g. 32K + ~7K for each zlib stream). As usual, EROFS ourperforms similar approaches too. Alternatively, DEFLATE could still be used for some specific files since EROFS supports multiple compression algorithms in one image. [1] https://developer.apple.com/documentation/compression/compression_algorithm Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20230810154859.118330-1-hsiangkao@linux.alibaba.com