Re: [syzbot] [virtualization?] KMSAN: uninit-value in virtqueue_add (4)

[Stefan Hajnoczi]

On Tue, Jan 02, 2024 at 08:03:46AM -0500, Michael S. Tsirkin wrote:
> On Mon, Jan 01, 2024 at 05:38:24AM -0800, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    fbafc3e621c3 Merge tag 'for_linus' of git://git.kernel.org..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=173df3e9e80000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=e0c7078a6b901aa3
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d7521c1e3841ed075a42
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1300b4a1e80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=130b0379e80000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/1520f7b6daa4/disk-fbafc3e6.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/8b490af009d5/vmlinux-fbafc3e6.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/202ca200f4a4/bzImage-fbafc3e6.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+d7521c1e3841ed075a42@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 
> > =====================================================

Hi Alexander,
Please take a look at this KMSAN failure. The uninitialized memory was
created for the purpose of writing a coredump. vring_map_one_sg() should
have direction=DMA_TO_DEVICE.

I can't easily tell whether this is a genuine bug or an issue with
commit 88938359e2df ("virtio: kmsan: check/unpoison scatterlist in
vring_map_one_sg()"). Maybe coredump.c is writing out pages that KMSAN
thinks are uninitialized?

Stefan

> > BUG: KMSAN: uninit-value in vring_map_one_sg drivers/virtio/virtio_ring.c:380 [inline]
> > BUG: KMSAN: uninit-value in virtqueue_add_split drivers/virtio/virtio_ring.c:614 [inline]
> > BUG: KMSAN: uninit-value in virtqueue_add+0x21c6/0x6530 drivers/virtio/virtio_ring.c:2210
> >  vring_map_one_sg drivers/virtio/virtio_ring.c:380 [inline]
> >  virtqueue_add_split drivers/virtio/virtio_ring.c:614 [inline]
> >  virtqueue_add+0x21c6/0x6530 drivers/virtio/virtio_ring.c:2210
> >  virtqueue_add_sgs+0x186/0x1a0 drivers/virtio/virtio_ring.c:2244
> >  __virtscsi_add_cmd drivers/scsi/virtio_scsi.c:467 [inline]
> >  virtscsi_add_cmd+0x838/0xad0 drivers/scsi/virtio_scsi.c:501
> >  virtscsi_queuecommand+0x896/0xa60 drivers/scsi/virtio_scsi.c:598
> >  scsi_dispatch_cmd drivers/scsi/scsi_lib.c:1516 [inline]
> >  scsi_queue_rq+0x4874/0x5790 drivers/scsi/scsi_lib.c:1758
> >  blk_mq_dispatch_rq_list+0x13f8/0x3600 block/blk-mq.c:2049
> >  __blk_mq_do_dispatch_sched block/blk-mq-sched.c:170 [inline]
> >  blk_mq_do_dispatch_sched block/blk-mq-sched.c:184 [inline]
> >  __blk_mq_sched_dispatch_requests+0x10af/0x2500 block/blk-mq-sched.c:309
> >  blk_mq_sched_dispatch_requests+0x160/0x2d0 block/blk-mq-sched.c:333
> >  blk_mq_run_work_fn+0xd0/0x280 block/blk-mq.c:2434
> >  process_one_work kernel/workqueue.c:2627 [inline]
> >  process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700
> >  worker_thread+0xf45/0x1490 kernel/workqueue.c:2781
> >  kthread+0x3ed/0x540 kernel/kthread.c:388
> >  ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
> >  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> > 
> > Uninit was created at:
> >  __alloc_pages+0x9a4/0xe00 mm/page_alloc.c:4591
> >  alloc_pages_mpol+0x62b/0x9d0 mm/mempolicy.c:2133
> >  alloc_pages mm/mempolicy.c:2204 [inline]
> >  folio_alloc+0x1da/0x380 mm/mempolicy.c:2211
> >  filemap_alloc_folio+0xa5/0x430 mm/filemap.c:974
> >  __filemap_get_folio+0xa5a/0x1760 mm/filemap.c:1918
> >  ext4_da_write_begin+0x7f8/0xec0 fs/ext4/inode.c:2891
> >  generic_perform_write+0x3f5/0xc40 mm/filemap.c:3918
> >  ext4_buffered_write_iter+0x564/0xaa0 fs/ext4/file.c:299
> >  ext4_file_write_iter+0x20f/0x3460
> >  __kernel_write_iter+0x329/0x930 fs/read_write.c:517
> >  dump_emit_page fs/coredump.c:888 [inline]
> >  dump_user_range+0x593/0xcd0 fs/coredump.c:915
> >  elf_core_dump+0x528d/0x5a40 fs/binfmt_elf.c:2077
> >  do_coredump+0x32c9/0x4920 fs/coredump.c:764
> >  get_signal+0x2185/0x2d10 kernel/signal.c:2890
> >  arch_do_signal_or_restart+0x53/0xca0 arch/x86/kernel/signal.c:309
> >  exit_to_user_mode_loop+0xe8/0x320 kernel/entry/common.c:168
> >  exit_to_user_mode_prepare+0x163/0x220 kernel/entry/common.c:204
> >  irqentry_exit_to_user_mode+0xd/0x30 kernel/entry/common.c:309
> >  irqentry_exit+0x16/0x40 kernel/entry/common.c:412
> >  exc_page_fault+0x246/0x6f0 arch/x86/mm/fault.c:1564
> >  asm_exc_page_fault+0x2b/0x30 arch/x86/include/asm/idtentry.h:570
> > 
> > Bytes 0-4095 of 4096 are uninitialized
> > Memory access of size 4096 starts at ffff88812c79c000
> > 
> > CPU: 0 PID: 997 Comm: kworker/0:1H Not tainted 6.7.0-rc7-syzkaller-00003-gfbafc3e621c3 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> > Workqueue: kblockd blk_mq_run_work_fn
> > =====================================================
> > 
> > 
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > 
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> > 
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
> > 
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> > 
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> > 
> > If you want to undo deduplication, reply with:
> > #syz undup
>

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