[PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Laurent Dufour]

The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
reserved to the Ultravisor.

However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
context of the VM calling UV_ESM. This allows the Hypervisor to return to
the guest without going through the Ultravisor. Thus the Secure bit of SRR1
is not set in that particular case.

In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
not set in that case.

Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 93493f0cbfe8..eb1f96cb7b72 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1099,9 +1099,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 			ret = kvmppc_h_svm_init_done(vcpu->kvm);
 		break;
 	case H_SVM_INIT_ABORT:
-		ret = H_UNSUPPORTED;
-		if (kvmppc_get_srr1(vcpu) & MSR_S)
-			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
+		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
 		break;
 
 	default:
-- 
2.26.2

Re: [PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Greg Kurz]

On Wed, 20 May 2020 18:51:10 +0200
Laurent Dufour <ldufour@linux.ibm.com> wrote:

> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
> reserved to the Ultravisor.
> 
> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
> context of the VM calling UV_ESM. This allows the Hypervisor to return to
> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
> is not set in that particular case.
> 
> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
> not set in that case.
> 

Why not checking vcpu->kvm->arch.secure_guest then ?

> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> ---
>  arch/powerpc/kvm/book3s_hv.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 93493f0cbfe8..eb1f96cb7b72 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1099,9 +1099,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>  			ret = kvmppc_h_svm_init_done(vcpu->kvm);
>  		break;
>  	case H_SVM_INIT_ABORT:
> -		ret = H_UNSUPPORTED;
> -		if (kvmppc_get_srr1(vcpu) & MSR_S)
> -			ret = kvmppc_h_svm_init_abort(vcpu->kvm);

or at least put a comment to explain why H_SVM_INIT_ABORT
doesn't have the same sanity check as the other SVM hcalls.

> +		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
>  		break;
>  
>  	default:

Re: [PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Laurent Dufour]

Le 20/05/2020 à 19:32, Greg Kurz a écrit :
> On Wed, 20 May 2020 18:51:10 +0200
> Laurent Dufour <ldufour@linux.ibm.com> wrote:
> 
>> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
>> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
>> reserved to the Ultravisor.
>>
>> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
>> context of the VM calling UV_ESM. This allows the Hypervisor to return to
>> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
>> is not set in that particular case.
>>
>> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
>> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
>> not set in that case.
>>
> 
> Why not checking vcpu->kvm->arch.secure_guest then ?

I don't think that's the right place.
> 
>> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>> ---
>>   arch/powerpc/kvm/book3s_hv.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 93493f0cbfe8..eb1f96cb7b72 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -1099,9 +1099,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>>   			ret = kvmppc_h_svm_init_done(vcpu->kvm);
>>   		break;
>>   	case H_SVM_INIT_ABORT:
>> -		ret = H_UNSUPPORTED;
>> -		if (kvmppc_get_srr1(vcpu) & MSR_S)
>> -			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
> 
> or at least put a comment to explain why H_SVM_INIT_ABORT
> doesn't have the same sanity check as the other SVM hcalls.

I agree that might help. I'll send a v2 with a comment there.

> 
>> +		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
>>   		break;
>>   
>>   	default:
> 

[PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Laurent Dufour]

The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
reserved to the Ultravisor.

However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
context of the VM calling UV_ESM. This allows the Hypervisor to return to
the guest without going through the Ultravisor. Thus the Secure bit of SRR1
is not set in that particular case.

In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
not set in that case.

Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 93493f0cbfe8..6ad1a3b14300 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1099,9 +1099,12 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 			ret = kvmppc_h_svm_init_done(vcpu->kvm);
 		break;
 	case H_SVM_INIT_ABORT:
-		ret = H_UNSUPPORTED;
-		if (kvmppc_get_srr1(vcpu) & MSR_S)
-			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
+		/*
+		 * Even if that call is made by the Ultravisor, the SSR1 value
+		 * is the guest context one, with the secure bit clear as it has
+		 * not yet been secured. So we can't check it here.
+		 */
+		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
 		break;
 
 	default:
-- 
2.26.2

Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Greg Kurz]

On Wed, 20 May 2020 19:43:08 +0200
Laurent Dufour <ldufour@linux.ibm.com> wrote:

> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
> reserved to the Ultravisor.
> 
> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
> context of the VM calling UV_ESM. This allows the Hypervisor to return to
> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
> is not set in that particular case.
> 
> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
> not set in that case.
> 
> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  arch/powerpc/kvm/book3s_hv.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 93493f0cbfe8..6ad1a3b14300 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1099,9 +1099,12 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>  			ret = kvmppc_h_svm_init_done(vcpu->kvm);
>  		break;
>  	case H_SVM_INIT_ABORT:
> -		ret = H_UNSUPPORTED;
> -		if (kvmppc_get_srr1(vcpu) & MSR_S)
> -			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
> +		/*
> +		 * Even if that call is made by the Ultravisor, the SSR1 value
> +		 * is the guest context one, with the secure bit clear as it has
> +		 * not yet been secured. So we can't check it here.
> +		 */
> +		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
>  		break;
>  
>  	default:

Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Ram Pai]

On Wed, May 20, 2020 at 07:43:08PM +0200, Laurent Dufour wrote:
> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
> reserved to the Ultravisor.
> 
> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
> context of the VM calling UV_ESM. This allows the Hypervisor to return to
> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
> is not set in that particular case.
> 
> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
> not set in that case.
> 
> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>


Reviewed-by: Ram Pai <linuxram@us.ibm.com>

> ---
>  arch/powerpc/kvm/book3s_hv.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 93493f0cbfe8..6ad1a3b14300 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1099,9 +1099,12 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>  			ret = kvmppc_h_svm_init_done(vcpu->kvm);
>  		break;
>  	case H_SVM_INIT_ABORT:
> -		ret = H_UNSUPPORTED;
> -		if (kvmppc_get_srr1(vcpu) & MSR_S)
> -			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
> +		/*
> +		 * Even if that call is made by the Ultravisor, the SSR1 value
> +		 * is the guest context one, with the secure bit clear as it has
> +		 * not yet been secured. So we can't check it here.
> +		 */

Frankly speaking, the comment above when read in isolation; i.e without
the delete code above, feels out of place.  The reasoning for change is
anyway captured in the changelog.  So, I think, we should delete this
comment.

Also the comment above assumes the Ultravisor will call H_SVM_INIT_ABORT
with SRR1(S) bit not set; which may or may not be true.  Regardless of
who and how H_SVM_INIT_ABORT is called, we should just call
kvmppc_h_svm_init_abort() and let it deal with the complexities.


RP

Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Paul Mackerras]

On Wed, May 20, 2020 at 07:43:08PM +0200, Laurent Dufour wrote:
> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
> reserved to the Ultravisor.
> 
> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
> context of the VM calling UV_ESM. This allows the Hypervisor to return to
> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
> is not set in that particular case.
> 
> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
> not set in that case.
> 
> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>

Thanks, applied to my kvm-ppc-next branch.  I expanded the comment in
the code a little.

Paul.

Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

[Laurent Dufour]

Le 27/05/2020 à 06:16, Paul Mackerras a écrit :
> On Wed, May 20, 2020 at 07:43:08PM +0200, Laurent Dufour wrote:
>> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
>> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
>> reserved to the Ultravisor.
>>
>> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
>> context of the VM calling UV_ESM. This allows the Hypervisor to return to
>> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
>> is not set in that particular case.
>>
>> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
>> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
>> not set in that case.
>>
>> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> 
> Thanks, applied to my kvm-ppc-next branch.  I expanded the comment in
> the code a little.

Thanks, the comment is more explicit now.

Laurent.