Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT
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
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.
Re: [PATCH v2] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT
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
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
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
Reviewed-by: Ram Pai
> ---
> 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
On Wed, 20 May 2020 19:43:08 +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
> ---
Reviewed-by: Greg Kurz
> 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:
