Hi Will,
On Thu, Aug 12, 2021 at 11:57 AM Will Deacon <will@xxxxxxxxxx> wrote:
>
> On Mon, Jul 19, 2021 at 05:03:45PM +0100, Fuad Tabba 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.
> >
> > Adapted from commit 22f553842b14 ("KVM: arm64: Handle Asymmetric
> > AArch32 systems")
> >
> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> > ---
> > arch/arm64/kvm/hyp/include/hyp/switch.h | 24 ++++++++++++++++++++++++
> > 1 file changed, 24 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> > index 8431f1514280..f09343e15a80 100644
> > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> > @@ -23,6 +23,7 @@
> > #include <asm/kprobes.h>
> > #include <asm/kvm_asm.h>
> > #include <asm/kvm_emulate.h>
> > +#include <asm/kvm_fixed_config.h>
> > #include <asm/kvm_hyp.h>
> > #include <asm/kvm_mmu.h>
> > #include <asm/fpsimd.h>
> > @@ -477,6 +478,29 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> > write_sysreg_el2(read_sysreg_el2(SYS_ELR) - 4, SYS_ELR);
> > }
> >
> > + /*
> > + * Protected VMs might not be allowed to run in AArch32. The check below
> > + * is based on the one in kvm_arch_vcpu_ioctl_run().
> > + * The ARMv8 architecture doesn't 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.
> > + */
> > + if (unlikely(is_nvhe_hyp_code() &&
> > + kvm_vm_is_protected(kern_hyp_va(vcpu->kvm)) &&
> > + FIELD_GET(FEATURE(ID_AA64PFR0_EL0),
> > + PVM_ID_AA64PFR0_ALLOW) <
> > + ID_AA64PFR0_ELx_32BIT_64BIT &&
> > + 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.
> > + */
> > + vcpu->arch.target = -1;
> > + *exit_code = ARM_EXCEPTION_IL;
> > + goto exit;
> > + }
>
> Would this be better off inside the nvhe-specific run loop? Seems like we
> could elide fixup_guest_exit() altogether if we've detect that we're in
> AArch32 state when we shouldn't be and it would keep the code off the shared
> path.
Yes, it makes more sense and would result in cleaner code to have it
there, especially in the future where there's likely to be a separate
run loop for protected VMs. I'll move it.
Thanks,
/fuad
> Will
