On Sun, 10 Oct 2021 15:56:36 +0100, Fuad Tabba <tabba@xxxxxxxxxx> wrote: > > Protected KVM does not support protected AArch32 guests. However, > it is possible for the guest to force run AArch32, potentially > causing problems. Add an extra check so that if the hypervisor > catches the guest doing that, it can prevent the guest from > running again by resetting vcpu->arch.target and returning > ARM_EXCEPTION_IL. > > If this were to happen, The VMM can try and fix it by re- > initializing the vcpu with KVM_ARM_VCPU_INIT, however, this is > likely not possible for protected VMs. > > Adapted from commit 22f553842b14 ("KVM: arm64: Handle Asymmetric > AArch32 systems") > > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx> > --- > arch/arm64/kvm/hyp/nvhe/switch.c | 34 ++++++++++++++++++++++++++++++++ > 1 file changed, 34 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c > index 2c72c31e516e..f25b6353a598 100644 > --- a/arch/arm64/kvm/hyp/nvhe/switch.c > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c > @@ -232,6 +232,37 @@ static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm *kvm) > return hyp_exit_handlers; > } > > +/* > + * Some guests (e.g., protected VMs) are not be allowed to run in AArch32. > + * The ARMv8 architecture does not give the hypervisor a mechanism to prevent a > + * guest from dropping to AArch32 EL0 if implemented by the CPU. If the > + * hypervisor spots a guest in such a state ensure it is handled, and don't > + * trust the host to spot or fix it. The check below is based on the one in > + * kvm_arch_vcpu_ioctl_run(). > + * > + * Returns false if the guest ran in AArch32 when it shouldn't have, and > + * thus should exit to the host, or true if a the guest run loop can continue. > + */ > +static bool handle_aarch32_guest(struct kvm_vcpu *vcpu, u64 *exit_code) > +{ > + struct kvm *kvm = kern_hyp_va(vcpu->kvm); > + > + if (kvm_vm_is_protected(kvm) && vcpu_mode_is_32bit(vcpu)) { > + /* > + * As we have caught the guest red-handed, decide that it isn't > + * fit for purpose anymore by making the vcpu invalid. The VMM > + * can try and fix it by re-initializing the vcpu with > + * KVM_ARM_VCPU_INIT, however, this is likely not possible for > + * protected VMs. > + */ > + vcpu->arch.target = -1; > + *exit_code = ARM_EXCEPTION_IL; Aren't we losing a potential SError here, which the original commit doesn't need to handle? I'd expect something like: *exit_code &= BIT(ARM_EXIT_WITH_SERROR_BIT); *exit_code |= ARM_EXCEPTION_IL; > + return false; > + } > + > + return true; > +} > + > /* Switch to the guest for legacy non-VHE systems */ > int __kvm_vcpu_run(struct kvm_vcpu *vcpu) > { > @@ -294,6 +325,9 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu) > /* Jump in the fire! */ > exit_code = __guest_enter(vcpu); > > + if (unlikely(!handle_aarch32_guest(vcpu, &exit_code))) > + break; > + > /* And we're baaack! */ > } while (fixup_guest_exit(vcpu, &exit_code)); > Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm