* [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN
@ 2020-09-11 9:31 Vitaly Kuznetsov
2020-09-11 16:04 ` Sean Christopherson
2020-09-11 17:25 ` Paolo Bonzini
0 siblings, 2 replies; 4+ messages in thread
From: Vitaly Kuznetsov @ 2020-09-11 9:31 UTC (permalink / raw)
To: kvm, Paolo Bonzini
Cc: Sean Christopherson, Wanpeng Li, Jim Mattson,
Dr . David Alan Gilbert, linux-kernel
Even without in-kernel LAPIC we should allow writing '0' to
MSR_KVM_ASYNC_PF_EN as we're not enabling the mechanism. In
particular, QEMU with 'kernel-irqchip=off' fails to start
a guest with
qemu-system-x86_64: error: failed to set MSR 0x4b564d02 to 0x0
Fixes: 9d3c447c72fb2 ("KVM: X86: Fix async pf caused null-ptr-deref")
Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/x86.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d39d6cf1d473..44a86f7f2397 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2730,9 +2730,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
if (data & 0x30)
return 1;
- if (!lapic_in_kernel(vcpu))
- return 1;
-
vcpu->arch.apf.msr_en_val = data;
if (!kvm_pv_async_pf_enabled(vcpu)) {
@@ -2741,6 +2738,9 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
return 0;
}
+ if (!lapic_in_kernel(vcpu))
+ return 1;
+
if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
sizeof(u64)))
return 1;
--
2.25.4
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN
2020-09-11 9:31 [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN Vitaly Kuznetsov
@ 2020-09-11 16:04 ` Sean Christopherson
2020-09-11 17:27 ` Paolo Bonzini
2020-09-11 17:25 ` Paolo Bonzini
1 sibling, 1 reply; 4+ messages in thread
From: Sean Christopherson @ 2020-09-11 16:04 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: kvm, Paolo Bonzini, Wanpeng Li, Jim Mattson,
Dr . David Alan Gilbert, linux-kernel
On Fri, Sep 11, 2020 at 11:31:47AM +0200, Vitaly Kuznetsov wrote:
> Even without in-kernel LAPIC we should allow writing '0' to
> MSR_KVM_ASYNC_PF_EN as we're not enabling the mechanism. In
> particular, QEMU with 'kernel-irqchip=off' fails to start
> a guest with
>
> qemu-system-x86_64: error: failed to set MSR 0x4b564d02 to 0x0
>
> Fixes: 9d3c447c72fb2 ("KVM: X86: Fix async pf caused null-ptr-deref")
> Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/x86.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d39d6cf1d473..44a86f7f2397 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2730,9 +2730,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> if (data & 0x30)
> return 1;
>
> - if (!lapic_in_kernel(vcpu))
> - return 1;
> -
> vcpu->arch.apf.msr_en_val = data;
>
> if (!kvm_pv_async_pf_enabled(vcpu)) {
> @@ -2741,6 +2738,9 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> return 0;
> }
>
> + if (!lapic_in_kernel(vcpu))
This doesn't actually verify that @data == 0. kvm_pv_async_pf_enabled()
returns true iff KVM_ASYNC_PF_ENABLED and KVM_ASYNC_PF_DELIVERY_AS_INT are
set, e.g. this would allow setting one and not the other. This also allows
userspace to set vcpu->arch.apf.msr_en_val to an unsupported value, i.e.
@data has already been propagated to the vcpu and isn't unwound.
Why not just pivot on @data when lapic_in_kernel() is false? vcpu->arch.apic
is immutable so there's no need to update apf.msr_en_val in either direction.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 539ea1cd6020..36969d5ec291 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2735,7 +2735,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
return 1;
if (!lapic_in_kernel(vcpu))
- return 1;
+ return data ? 1 : 0;
vcpu->arch.apf.msr_en_val = data;
> + return 1;
> +
> if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
> sizeof(u64)))
> return 1;
> --
> 2.25.4
>
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN
2020-09-11 16:04 ` Sean Christopherson
@ 2020-09-11 17:27 ` Paolo Bonzini
0 siblings, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2020-09-11 17:27 UTC (permalink / raw)
To: Sean Christopherson, Vitaly Kuznetsov
Cc: kvm, Wanpeng Li, Jim Mattson, Dr . David Alan Gilbert, linux-kernel
On 11/09/20 18:04, Sean Christopherson wrote:
> This doesn't actually verify that @data == 0. kvm_pv_async_pf_enabled()
> returns true iff KVM_ASYNC_PF_ENABLED and KVM_ASYNC_PF_DELIVERY_AS_INT are
> set, e.g. this would allow setting one and not the other. This also allows
> userspace to set vcpu->arch.apf.msr_en_val to an unsupported value, i.e.
> @data has already been propagated to the vcpu and isn't unwound.
>
> Why not just pivot on @data when lapic_in_kernel() is false? vcpu->arch.apic
> is immutable so there's no need to update apf.msr_en_val in either direction.
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 539ea1cd6020..36969d5ec291 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2735,7 +2735,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> return 1;
>
> if (!lapic_in_kernel(vcpu))
> - return 1;
> + return data ? 1 : 0;
>
> vcpu->arch.apf.msr_en_val = data;
>
>
>> + return 1;
>> +
>> if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
>> sizeof(u64)))
>> return 1;
>> --
>> 2.25.4
>>
>
Committed this instead, though.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN
2020-09-11 9:31 [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN Vitaly Kuznetsov
2020-09-11 16:04 ` Sean Christopherson
@ 2020-09-11 17:25 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2020-09-11 17:25 UTC (permalink / raw)
To: Vitaly Kuznetsov, kvm
Cc: Sean Christopherson, Wanpeng Li, Jim Mattson,
Dr . David Alan Gilbert, linux-kernel
On 11/09/20 11:31, Vitaly Kuznetsov wrote:
> Even without in-kernel LAPIC we should allow writing '0' to
> MSR_KVM_ASYNC_PF_EN as we're not enabling the mechanism. In
> particular, QEMU with 'kernel-irqchip=off' fails to start
> a guest with
>
> qemu-system-x86_64: error: failed to set MSR 0x4b564d02 to 0x0
>
> Fixes: 9d3c447c72fb2 ("KVM: X86: Fix async pf caused null-ptr-deref")
> Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/x86.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d39d6cf1d473..44a86f7f2397 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2730,9 +2730,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> if (data & 0x30)
> return 1;
>
> - if (!lapic_in_kernel(vcpu))
> - return 1;
> -
> vcpu->arch.apf.msr_en_val = data;
>
> if (!kvm_pv_async_pf_enabled(vcpu)) {
> @@ -2741,6 +2738,9 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> return 0;
> }
>
> + if (!lapic_in_kernel(vcpu))
> + return 1;
> +
> if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
> sizeof(u64)))
> return 1;
>
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-09-11 17:27 UTC | newest]
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2020-09-11 9:31 [PATCH] KVM: x86: always allow writing '0' to MSR_KVM_ASYNC_PF_EN Vitaly Kuznetsov
2020-09-11 16:04 ` Sean Christopherson
2020-09-11 17:27 ` Paolo Bonzini
2020-09-11 17:25 ` Paolo Bonzini
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