Re: kvm: WARNING in mmu_spte_clear_track_bits

Dmitry Vyukov
2017-03-12T11:21:04Z

On Tue, Jan 17, 2017 at 5:00 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Jan 17, 2017 at 4:20 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>>
>> On 13/01/2017 12:15, Dmitry Vyukov wrote:
>>>
>>> I've commented out the WARNING for now, but I am seeing lots of
>>> use-after-free's and rcu stalls involving mmu_spte_clear_track_bits:
>>>
>>>
>>> BUG: KASAN: use-after-free in mmu_spte_clear_track_bits+0x186/0x190
>>> arch/x86/kvm/mmu.c:597 at addr ffff880068ae2008
>>> Read of size 8 by task syz-executor2/16715
>>> page:ffffea00016e6170 count:0 mapcount:0 mapping: (null) index:0x0
>>> flags: 0x500000000000000()
>>> raw: 0500000000000000 0000000000000000 0000000000000000 00000000ffffffff
>>> raw: ffffea00017ec5a0 ffffea0001783d48 ffff88006aec5d98
>>> page dumped because: kasan: bad access detected
>>> CPU: 2 PID: 16715 Comm: syz-executor2 Not tainted 4.10.0-rc3+ #163
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>> Call Trace:
>>> __dump_stack lib/dump_stack.c:15 [inline]
>>> dump_stack+0x292/0x3a2 lib/dump_stack.c:51
>>> kasan_report_error mm/kasan/report.c:213 [inline]
>>> kasan_report+0x42d/0x460 mm/kasan/report.c:307
>>> __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:333
>>> mmu_spte_clear_track_bits+0x186/0x190 arch/x86/kvm/mmu.c:597
>>> drop_spte+0x24/0x280 arch/x86/kvm/mmu.c:1182
>>> kvm_zap_rmapp+0x119/0x260 arch/x86/kvm/mmu.c:1401
>>> kvm_unmap_rmapp+0x1d/0x30 arch/x86/kvm/mmu.c:1412
>>> kvm_handle_hva_range+0x54a/0x7d0 arch/x86/kvm/mmu.c:1565
>>> kvm_unmap_hva_range+0x2e/0x40 arch/x86/kvm/mmu.c:1591
>>> kvm_mmu_notifier_invalidate_range_start+0xae/0x140
>>> arch/x86/kvm/../../../virt/kvm/kvm_main.c:360
>>> __mmu_notifier_invalidate_range_start+0x1f8/0x300 mm/mmu_notifier.c:199
>>> mmu_notifier_invalidate_range_start include/linux/mmu_notifier.h:282 [inline]
>>> unmap_vmas+0x14b/0x1b0 mm/memory.c:1368
>>> unmap_region+0x2f8/0x560 mm/mmap.c:2460
>>> do_munmap+0x7b8/0xfa0 mm/mmap.c:2657
>>> mmap_region+0x68f/0x18e0 mm/mmap.c:1612
>>> do_mmap+0x6a2/0xd40 mm/mmap.c:1450
>>> do_mmap_pgoff include/linux/mm.h:2031 [inline]
>>> vm_mmap_pgoff+0x1a9/0x200 mm/util.c:305
>>> SYSC_mmap_pgoff mm/mmap.c:1500 [inline]
>>> SyS_mmap_pgoff+0x22c/0x5d0 mm/mmap.c:1458
>>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
>>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
>>> entry_SYSCALL_64_fastpath+0x1f/0xc2
>>> RIP: 0033:0x445329
>>> RSP: 002b:00007fb33933cb58 EFLAGS: 00000282 ORIG_RAX: 0000000000000009
>>> RAX: ffffffffffffffda RBX: 0000000020000000 RCX: 0000000000445329
>>> RDX: 0000000000000003 RSI: 0000000000af1000 RDI: 0000000020000000
>>> RBP: 00000000006dfe90 R08: ffffffffffffffff R09: 0000000000000000
>>> R10: 0000000000000032 R11: 0000000000000282 R12: 0000000000700000
>>> R13: 0000000000000006 R14: ffffffffffffffff R15: 0000000020001000
>>> Memory state around the buggy address:
>>> ffff880068ae1f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> ffff880068ae1f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>> ffff880068ae2000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>> ^
>>> ffff880068ae2080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>> ffff880068ae2100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>> ==================================================================
>>
>> This could be related to the gfn_to_rmap issues.
>
>
> Humm... That's possible. Potentially I am not seeing any more of
> spte-related crashes after I applied the following patch:
>
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -968,8 +968,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> /* Check for overlaps */
> r = -EEXIST;
> kvm_for_each_memslot(slot, __kvm_memslots(kvm, as_id)) {
> - if ((slot->id >= KVM_USER_MEM_SLOTS) ||
> - (slot->id == id))
> + if (slot->id == id)
> continue;
> if (!((base_gfn + npages <= slot->base_gfn) ||
> (base_gfn >= slot->base_gfn + slot->npages)))

Friendly ping. Just hit it on
mmotm/86292b33d4b79ee03e2f43ea0381ef85f077c760 (without the above
change):

------------[ cut here ]------------
WARNING: CPU: 1 PID: 31060 at arch/x86/kvm/mmu.c:682
mmu_spte_clear_track_bits+0x3a1/0x420 arch/x86/kvm/mmu.c:682
CPU: 1 PID: 31060 Comm: syz-executor0 Not tainted 4.11.0-rc1+ #328
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x1a7/0x26a lib/dump_stack.c:52
panic+0x1f8/0x40f kernel/panic.c:180
__warn+0x1c4/0x1e0 kernel/panic.c:541
warn_slowpath_null+0x2c/0x40 kernel/panic.c:584
mmu_spte_clear_track_bits+0x3a1/0x420 arch/x86/kvm/mmu.c:682
drop_spte+0x24/0x280 arch/x86/kvm/mmu.c:1323
mmu_page_zap_pte+0x223/0x350 arch/x86/kvm/mmu.c:2438
kvm_mmu_page_unlink_children arch/x86/kvm/mmu.c:2460 [inline]
kvm_mmu_prepare_zap_page+0x1ce/0x13d0 arch/x86/kvm/mmu.c:2504
kvm_zap_obsolete_pages arch/x86/kvm/mmu.c:5134 [inline]
kvm_mmu_invalidate_zap_all_pages+0x4d4/0x6b0 arch/x86/kvm/mmu.c:5175
kvm_arch_flush_shadow_all+0x15/0x20 arch/x86/kvm/x86.c:8364
kvm_mmu_notifier_release+0x71/0xb0
arch/x86/kvm/../../../virt/kvm/kvm_main.c:472
__mmu_notifier_release+0x1e5/0x6b0 mm/mmu_notifier.c:75
mmu_notifier_release include/linux/mmu_notifier.h:235 [inline]
exit_mmap+0x3a3/0x470 mm/mmap.c:2941
__mmput kernel/fork.c:890 [inline]
mmput+0x228/0x700 kernel/fork.c:912
exit_mm kernel/exit.c:558 [inline]
do_exit+0x9e8/0x1c20 kernel/exit.c:866
do_group_exit+0x149/0x400 kernel/exit.c:983
get_signal+0x6d9/0x1840 kernel/signal.c:2318
do_signal+0x94/0x1f30 arch/x86/kernel/signal.c:808
exit_to_usermode_loop+0x1e5/0x2d0 arch/x86/entry/common.c:157
prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
entry_SYSCALL_64_fastpath+0xc0/0xc2
RIP: 0033:0x4458d9
RSP: 002b:00007ffa472c3b58 EFLAGS: 00000286 ORIG_RAX: 00000000000000ce
RAX: fffffffffffffff4 RBX: 0000000000708000 RCX: 00000000004458d9
RDX: 0000000000000000 RSI: 000000002006bff8 RDI: 000000000000a05b
RBP: 0000000000000fe0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000006df0a0
R13: 000000000000a05b R14: 000000002006bff8 R15: 0000000000000000