[v3] KVM: hyperv: Fix Direct Synthetic timers assert an interrupt w/o lapic_in_kernel
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Message ID 1568619752-3885-1-git-send-email-wanpengli@tencent.com
State New
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  • [v3] KVM: hyperv: Fix Direct Synthetic timers assert an interrupt w/o lapic_in_kernel
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Commit Message

Wanpeng Li Sept. 16, 2019, 7:42 a.m. UTC
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.

syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=1752fe0a600000

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>
---
v2 -> v3:
 * add the link of syzkaller source
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(-)

Comments

Vitaly Kuznetsov Sept. 16, 2019, 8:55 a.m. UTC | #1
Wanpeng Li <kernellwp@gmail.com> writes:

> 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.
>
> syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=1752fe0a600000
>
> 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>
> ---
> v2 -> v3:
>  * add the link of syzkaller source
> 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;

We can go even further and forbid to enable direct mode by adding
lapic_in_kernel() check to stimer_set_config() but the guest (or
userspace setting CPUIDs) is already misbehaving and we can't magically
fix things in KVM.

>  }
>  
>  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;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Paolo Bonzini Sept. 17, 2019, 1:38 p.m. UTC | #2
On 16/09/19 09:42, 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.
> 
> syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=1752fe0a600000
> 
> 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>
> ---
> v2 -> v3:
>  * add the link of syzkaller source
> 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;
>  
> 

Queued, thanks.

Paolo

Patch
diff mbox series

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;