Re: BUG: unable to handle kernel paging request in __kvm_mmu_prepare_zap_page

[Dmitry Vyukov <dvyukov@google.com>]

> Sean Christopherson wrote:
> On Mon, Feb 25, 2019 at 06:50:05AM -0800, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: 94a47529a645 Add linux-next specific files for 20190222
> > git tree: linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13c1c692c00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=51cd1c8c39e8a207
> > dashboard link: https://syzkaller.appspot.com/bug?extid=222746e0104bbb617d51
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11fcba7cc00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+222746...@syzkaller.appspotmail.com
> >
> > BUG: unable to handle kernel paging request at ffff88809c0e1000
> > #PF error: [PROT] [WRITE] [RSVD]
> > PGD b201067 P4D b201067 PUD 21ffff067 PMD 800000009c0001e3
> > Oops: 000b [#1] PREEMPT SMP KASAN
> > CPU: 1 PID: 7863 Comm: syz-executor.2 Not tainted 5.0.0-rc7-next-20190222
> > #41
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: 0010:__write_once_size include/linux/compiler.h:224 [inline]
> > RIP: 0010:__update_clear_spte_fast arch/x86/kvm/mmu.c:558 [inline]
> > RIP: 0010:mmu_spte_clear_no_track arch/x86/kvm/mmu.c:859 [inline]
> > RIP: 0010:drop_parent_pte arch/x86/kvm/mmu.c:2051 [inline]
> > RIP: 0010:kvm_mmu_unlink_parents arch/x86/kvm/mmu.c:2645 [inline]
> > RIP: 0010:__kvm_mmu_prepare_zap_page+0x1ee/0x11a0 arch/x86/kvm/mmu.c:2683
> > Code: f8 30 60 00 48 89 de 4c 89 e7 e8 bd ad fe ff 4c 89 e0 48 b9 00 00 00
> > 00 00 fc ff df 48 c1 e8 03 80 3c 08 00 0f 85 a5 0d 00 00 <49> c7 04 24 00 00
> > 00 00 e8 c5 30 60 00 4c 89 ea 4c 89 fe 48 89 df
> > RSP: 0018:ffff88809e96faf0 EFLAGS: 00010246
> > RAX: 1ffff1101381c200 RBX: ffff888098149820 RCX: dffffc0000000000
> > RDX: 0000000000000000 RSI: ffffffff810ed2f4 RDI: 0000000000000007
> > RBP: ffff88809e96fbd0 R08: ffff888094052700 R09: ffffed100e339d92
> > R10: ffffed100e339d91 R11: ffff8880719cec8b R12: ffff88809c0e1000
> > R13: ffff88809e96fb70 R14: ffffc90006a39000 R15: ffff88809e96fb68
> > FS: 000000000239b940(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: ffff88809c0e1000 CR3: 00000000a143a000 CR4: 00000000001426e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > __kvm_mmu_zap_all+0x1f6/0x350 arch/x86/kvm/mmu.c:5856
>
> This strongly suggests the recent MMU zapping changes[1] are to blame,
> but I haven't had any luck reproducing the bug.
>
> Paolo, were you able to make any headway on the kvm-unit-test issues
> that are potentially due to the MMU changes?
>
> [1] https://patchwork.kernel.org/cover/10798425/

Something has fixed this, let's consider it's this (I did not find any
better candidate):

#syz fix:
KVM: x86: fix handling of role.cr4_pae and rename it to 'gpte_size'


> > kvm_mmu_zap_all+0x18/0x20 arch/x86/kvm/mmu.c:5870
> > kvm_arch_flush_shadow_all+0x16/0x20 arch/x86/kvm/x86.c:9473
> > kvm_mmu_notifier_release+0x63/0xb0
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:499
> > mmu_notifier_unregister+0x137/0x440 mm/mmu_notifier.c:356
> > kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:745 [inline]
> > kvm_put_kvm+0x553/0xc70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:770
> > kvm_vcpu_release+0x7b/0xa0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2500
> > __fput+0x2e5/0x8d0 fs/file_table.c:278
> > ____fput+0x16/0x20 fs/file_table.c:309
> > task_work_run+0x14a/0x1c0 kernel/task_work.c:113
> > tracehook_notify_resume include/linux/tracehook.h:188 [inline]
> > exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
> > prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
> > syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
> > do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x411d31
> > Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 94 19 00 00 c3 48
> > 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89
> > c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> > RSP: 002b:00007ffe9da10de0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> > RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000411d31
> > RDX: 0000000000000000 RSI: 0000000000740528 RDI: 0000000000000005
> > RBP: 0000000000000000 R08: 0000000000740520 R09: 000000000000dec8
> > R10: 00007ffe9da10d00 R11: 0000000000000293 R12: 0000000000000000
> > R13: 0000000000000001 R14: 0000000000000007 R15: 0000000000000002
> > Modules linked in:
> > CR2: ffff88809c0e1000
> > ---[ end trace 4b53a3c1b491aa63 ]---
> > RIP: 0010:__write_once_size include/linux/compiler.h:224 [inline]
> > RIP: 0010:__update_clear_spte_fast arch/x86/kvm/mmu.c:558 [inline]
> > RIP: 0010:mmu_spte_clear_no_track arch/x86/kvm/mmu.c:859 [inline]
> > RIP: 0010:drop_parent_pte arch/x86/kvm/mmu.c:2051 [inline]
> > RIP: 0010:kvm_mmu_unlink_parents arch/x86/kvm/mmu.c:2645 [inline]
> > RIP: 0010:__kvm_mmu_prepare_zap_page+0x1ee/0x11a0 arch/x86/kvm/mmu.c:2683
> > Code: f8 30 60 00 48 89 de 4c 89 e7 e8 bd ad fe ff 4c 89 e0 48 b9 00 00 00
> > 00 00 fc ff df 48 c1 e8 03 80 3c 08 00 0f 85 a5 0d 00 00 <49> c7 04 24 00 00
> > 00 00 e8 c5 30 60 00 4c 89 ea 4c 89 fe 48 89 df
> > RSP: 0018:ffff88809e96faf0 EFLAGS: 00010246
> > RAX: 1ffff1101381c200 RBX: ffff888098149820 RCX: dffffc0000000000
> > RDX: 0000000000000000 RSI: ffffffff810ed2f4 RDI: 0000000000000007
> > RBP: ffff88809e96fbd0 R08: ffff888094052700 R09: ffffed100e339d92
> > R10: ffffed100e339d91 R11: ffff8880719cec8b R12: ffff88809c0e1000
> > R13: ffff88809e96fb70 R14: ffffc90006a39000 R15: ffff88809e96fb68
> > FS: 000000000239b940(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: ffff88809c0e1000 CR3: 00000000a143a000 CR4: 00000000001426e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >
> >
> > ---
> > This bug 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 syzk...@googlegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches