On Mon, Jan 2, 2017 at 7:01 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> On 02/01/2017 11:17, Dmitry Vyukov wrote:
>> On Mon, Jan 2, 2017 at 11:09 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>>
>>>
>>>
>>> On 01/01/2017 04:44, Wanpeng Li wrote:
>>>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>>>
>>>> This was reported by syzkaller:
>>>>
>>>> BUG: unable to handle kernel NULL pointer dereference at 00000000000001b0
>>>> IP: _raw_spin_lock+0xc/0x30
>>>> PGD 3e28eb067
>>>> PUD 3f0ac6067
>>>> PMD 0
>>>> Oops: 0002 [#1] SMP
>>>> CPU: 0 PID: 2431 Comm: test Tainted: G OE 4.10.0-rc1+ #3
>>>> Call Trace:
>>>> ? kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
>>>> kvm_arch_vcpu_ioctl_run+0x10a8/0x15f0 [kvm]
>>>> ? pick_next_task_fair+0xe1/0x4e0
>>>> ? kvm_arch_vcpu_load+0xea/0x260 [kvm]
>>>> kvm_vcpu_ioctl+0x33a/0x600 [kvm]
>>>> ? hrtimer_try_to_cancel+0x29/0x130
>>>> ? do_nanosleep+0x97/0xf0
>>>> do_vfs_ioctl+0xa1/0x5d0
>>>> ? __hrtimer_init+0x90/0x90
>>>> ? do_nanosleep+0x5b/0xf0
>>>> SyS_ioctl+0x79/0x90
>>>> do_syscall_64+0x6e/0x180
>>>> entry_SYSCALL64_slow_path+0x25/0x25
>>>> RIP: _raw_spin_lock+0xc/0x30 RSP: ffffa43688973cc0
>>>>
>>>> KVM will skip over create pic/ioapic if there is a created vCPU. However,
>>>> there is no guarantee whether ioapic is present when rescan ioapic which
>>>> results in NULL dereference ioapic->lock. This patch fix it by adding the
>>>> ioapic present check to ioapic scan.
>>>>
>>>> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>>>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
>>>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>>> ---
>>>> arch/x86/kvm/x86.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index 51ccfe0..9ca175c 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -6556,7 +6556,8 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>>>> else {
>>>> if (vcpu->arch.apicv_active)
>>>> kvm_x86_ops->sync_pir_to_irr(vcpu);
>>>> - kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>>>> + if (ioapic_irqchip(vcpu->kvm))
>>>> + kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>>>> }
>>>> bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
>>>> vcpu_to_synic(vcpu)->vec_bitmap, 256);
>>>
>>> Commit message for fuzzing bugs have usually included a beautified
>>> reproducer. However, you are not even saying if it is a race, or it is
>>> deterministic.
>>>
>>> The fix seems wrong to me at first impression, because "LAPIC enabled"
>>> and "irqchip not split" should imply the existence of an in-kernel
>>> IOAPIC. However, I cannot suggest the right course of action without
>>> seeing a testcase.
>>
>>
>>
>> I've created a reasonably beautified reproducer here:
>> https://groups.google.com/forum/#!msg/syzkaller/6V-KXaMDYi8/rOvBl-69DAAJ
>
> Thanks, this is beautiful enough. :)
>
> Hmm, the combination of 6c7caebc26c5 ("KVM: introduce
> kvm->created_vcpus", 2016-06-16) and 4c5ea0a9cd02 ("locking/static_key:
> Fix concurrent static_key_slow_inc()", 2016-06-24) should have fixed it
> for good.
>
> Is the ENABLE_CAP necessary to reproduce? Then, the bug is simply that
> the ENABLE_CAP should have failed without an irqchip (the
> KVM_CREATE_IRQCHIP in turn must have failed with EINVAL).
ENABLE_CAP is necessary to reproduce.
You are right KVM_CREATE_IRQCHIP fails with EINVAL:
ioctl(4, KVM_CREATE_IRQCHIP, 0) = -1 EINVAL (Invalid argument)
so I guess it is not necessary to reproduce.
It looks like ENABLE_CAP(KVM_CAP_HYPERV_SYNIC) badly races with exit in KVM_RUN.
>> FWIW the patch has fixed the crash, but there is another similar one
>> that happens slightly earlier:
>>
>> general protection fault: 0000 [#1] SMP KASAN
>> Dumping ftrace buffer:
>> (ftrace buffer empty)
>> Modules linked in:
>> CPU: 1 PID: 17462 Comm: syz-executor4 Not tainted 4.10.0-rc1+ #119
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> task: ffff88003d6a2280 task.stack: ffff8800357e8000
>> RIP: 0010:kvm_apic_hw_enabled arch/x86/kvm/lapic.h:156 [inline]
>> RIP: 0010:vcpu_scan_ioapic arch/x86/kvm/x86.c:6559 [inline]
>> RIP: 0010:vcpu_enter_guest arch/x86/kvm/x86.c:6691 [inline]
>> RIP: 0010:vcpu_run arch/x86/kvm/x86.c:6944 [inline]
>> RIP: 0010:kvm_arch_vcpu_ioctl_run+0x272c/0x4660 arch/x86/kvm/x86.c:7102
>> RSP: 0018:ffff8800357ef7d8 EFLAGS: 00010206
>> RAX: 0000000000000000 RBX: ffff88003a459170 RCX: ffffc90000a76000
>> RDX: 0000000000000014 RSI: ffffffff810ec1ce RDI: 00000000000000a0
>> RBP: ffff8800357efa50 R08: ffff88003d7f2560 R09: 0000000000000000
>> R10: 38260856151e7596 R11: dffffc0000000000 R12: dffffc0000000000
>> R13: ffff8800357ef9e0 R14: ffff88003a459140 R15: 0000000000000000
>> FS: 00007faa53a40700(0000) GS:ffff88003fd00000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000000000000 CR3: 000000003d5c6000 CR4: 00000000000026e0
>> Call Trace:
>> kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2569
>> vfs_ioctl fs/ioctl.c:43 [inline]
>> do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:683
>> SYSC_ioctl fs/ioctl.c:698 [inline]
>> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
>> entry_SYSCALL_64_fastpath+0x1f/0xc2
>> RIP: 0033:0x443a19
>> RSP: 002b:00007faa53a3fb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 0000000000000018 RCX: 0000000000443a19
>> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000018
>> RBP: 00000000006ddb30 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000286 R12: 00000000007000a8
>> R13: 00007faa53c23328 R14: 00007faa53c25358 R15: 0000000000000003
>> Code: e0 03 00 00 48 89 f8 48 c1 e8 03 42 80 3c 20 00 0f 85 82 1a 00
>> 00 49 8b 86 e0 03 00 00 48 8d b8 a0 00 00 00 48 89 fa 48 c1 ea 03 <42>
>> 80 3c 22 00 0f 85 3f 15 00 00 48 8b 80 a0 00 00 00 48 8d b8
>> RIP: kvm_apic_hw_enabled arch/x86/kvm/lapic.h:156 [inline] RSP: ffff8800357ef7d8
>> RIP: vcpu_scan_ioapic arch/x86/kvm/x86.c:6559 [inline] RSP: ffff8800357ef7d8
>> RIP: vcpu_enter_guest arch/x86/kvm/x86.c:6691 [inline] RSP: ffff8800357ef7d8
>> RIP: vcpu_run arch/x86/kvm/x86.c:6944 [inline] RSP: ffff8800357ef7d8
>> RIP: kvm_arch_vcpu_ioctl_run+0x272c/0x4660 arch/x86/kvm/x86.c:7102
>> RSP: ffff8800357ef7d8
>> ---[ end trace 72f3e29e9ea09f21 ]---
>> Kernel panic - not syncing: Fatal exception
>> Dumping ftrace buffer:
>> (ftrace buffer empty)
>> Kernel Offset: disabled
>>
>>
>> static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>> {
>> u64 eoi_exit_bitmap[4];
>>
>> if (!kvm_apic_hw_enabled(vcpu->arch.apic)) // <-----HERE
>> return;
>>
>>
>> static inline int kvm_apic_hw_enabled(struct kvm_lapic *apic)
>> {
>> if (static_key_false(&apic_hw_disabled.key))
>> return apic->vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE; // <--- HERE
>> return MSR_IA32_APICBASE_ENABLE;
>> }
>>
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