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SubjectRe: [PATCH v2 5/5] KVM: hyperv: Fix Direct Synthetic timers assert an interrupt w/o lapic_in_kernel
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On 06/09/19 03:30, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Reported by syzkaller:
>
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> RIP: 0010:__apic_accept_irq+0x46/0x740 arch/x86/kvm/lapic.c:1029
> Call Trace:
> kvm_apic_set_irq+0xb4/0x140 arch/x86/kvm/lapic.c:558
> stimer_notify_direct arch/x86/kvm/hyperv.c:648 [inline]
> stimer_expiration arch/x86/kvm/hyperv.c:659 [inline]
> kvm_hv_process_stimers+0x594/0x1650 arch/x86/kvm/hyperv.c:686
> vcpu_enter_guest+0x2b2a/0x54b0 arch/x86/kvm/x86.c:7896
> vcpu_run+0x393/0xd40 arch/x86/kvm/x86.c:8152
> kvm_arch_vcpu_ioctl_run+0x636/0x900 arch/x86/kvm/x86.c:8360
> kvm_vcpu_ioctl+0x6cf/0xaf0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2765
>
> The testcase programs HV_X64_MSR_STIMERn_CONFIG/HV_X64_MSR_STIMERn_COUNT,
> in addition, there is no lapic in the kernel, the counters value are small
> enough in order that kvm_hv_process_stimers() inject this already-expired
> timer interrupt into the guest through lapic in the kernel which triggers
> the NULL deferencing. This patch fixes it by don't advertise direct mode
> synthetic timers and discarding the inject when lapic is not in kernel.
>
> Reported-by: syzbot+dff25ee91f0c7d5c1695@syzkaller.appspotmail.com
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v1 -> v2:
> * don't advertise direct mode synthetic timers when lapic is not in kernel
>
> arch/x86/kvm/hyperv.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index c10a8b1..069e655 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -645,7 +645,9 @@ static int stimer_notify_direct(struct kvm_vcpu_hv_stimer *stimer)
> .vector = stimer->config.apic_vector
> };
>
> - return !kvm_apic_set_irq(vcpu, &irq, NULL);
> + if (lapic_in_kernel(vcpu))
> + return !kvm_apic_set_irq(vcpu, &irq, NULL);
> + return 0;
> }
>
> static void stimer_expiration(struct kvm_vcpu_hv_stimer *stimer)
> @@ -1849,7 +1851,13 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>
> ent->edx |= HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
> ent->edx |= HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;
> - ent->edx |= HV_STIMER_DIRECT_MODE_AVAILABLE;
> +
> + /*
> + * Direct Synthetic timers only make sense with in-kernel
> + * LAPIC
> + */
> + if (lapic_in_kernel(vcpu))
> + ent->edx |= HV_STIMER_DIRECT_MODE_AVAILABLE;
>
> break;
>
>

See replies to the previous version of the individual patches.

Paolo

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