[PATCH v3 10/15] KVM: arm64: nv: Reinject PAC exceptions caused by HCR_EL2.API==0

Marc Zyngier
2024-03-21T15:54:33Z

In order for a L1 hypervisor to correctly handle PAuth instructions,
it must observe traps caused by a L1 PAuth instruction when
HCR_EL2.API==0. Since we already handle the case for API==1 as
a fixup, only the exception injection case needs to be handled.

Rework the kvm_handle_ptrauth() callback to reinject the trap
in this case. Note that APK==0 is already handled by the exising
triage_sysreg_trap() helper.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/handle_exit.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 6a88ec024e2f..1ba2f788b2c3 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -214,12 +214,34 @@ static int handle_sve(struct kvm_vcpu *vcpu)
}

/*
- * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into
- * a NOP). If we get here, it is that we didn't fixup ptrauth on exit, and all
- * that we can do is give the guest an UNDEF.
+ * Two possibilities to handle a trapping ptrauth instruction:
+ *
+ * - Guest usage of a ptrauth instruction (which the guest EL1 did not
+ * turn into a NOP). If we get here, it is that we didn't fixup
+ * ptrauth on exit, and all that we can do is give the guest an
+ * UNDEF (as the guest isn't supposed to use ptrauth without being
+ * told it could).
+ *
+ * - Running an L2 NV guest while L1 has left HCR_EL2.API==0, and for
+ * which we reinject the exception into L1. API==1 is handled as a
+ * fixup so the only way to get here is when API==0.
+ *
+ * Anything else is an emulation bug (hence the WARN_ON + UNDEF).
*/
static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu)
{
+ if (!vcpu_has_ptrauth(vcpu)) {
+ kvm_inject_undefined(vcpu);
+ return 1;
+ }
+
+ if (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu)) {
+ kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
+ return 1;
+ }
+
+ /* Really shouldn't be here! */
+ WARN_ON_ONCE(1);
kvm_inject_undefined(vcpu);
return 1;
}
--
2.39.2