From 41011e2de3480f9adb6420b35b67628b2d903355 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Tue, 28 May 2024 11:06:31 +0100 Subject: KVM: arm64: nv: Fix relative priorities of exceptions generated by ERETAx ERETAx can fail in multiple ways: (1) ELR_EL2 points lalaland (2) we get a PAC failure (3) SPSR_EL2 has the wrong mode (1) is easy, as we just let the CPU do its thing and deliver an Instruction Abort. However, (2) and (3) are interesting, because the PAC failure priority is way below that of the Illegal Execution State exception. Which means that if we have detected a PAC failure (and that we have FPACCOMBINE), we must be careful to give priority to the Illegal Execution State exception, should one be pending. Solving this involves hoisting the SPSR calculation earlier and testing for the IL bit before injecting the FPAC exception. In the extreme case of a ERETAx returning to an invalid mode *and* failing its PAC check, we end up with an Instruction Abort (due to the new PC being mangled by the failed Auth) *and* PSTATE.IL being set. Which matches the requirements of the architecture. Whilst we're at it, remove a stale comment that states the obvious and only confuses the reader. Fixes: 213b3d1ea161 ("KVM: arm64: nv: Handle ERETA[AB] instructions") Reviewed-by: Joey Gouly Reviewed-by: Oliver Upton Link: https://lore.kernel.org/r/20240528100632.1831995-2-maz@kernel.org Signed-off-by: Marc Zyngier --- arch/arm64/kvm/emulate-nested.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) (limited to 'arch/arm64/kvm') diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c index 72d733c74a38..54090967a335 100644 --- a/arch/arm64/kvm/emulate-nested.c +++ b/arch/arm64/kvm/emulate-nested.c @@ -2181,16 +2181,23 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu) if (forward_traps(vcpu, HCR_NV)) return; + spsr = vcpu_read_sys_reg(vcpu, SPSR_EL2); + spsr = kvm_check_illegal_exception_return(vcpu, spsr); + /* Check for an ERETAx */ esr = kvm_vcpu_get_esr(vcpu); if (esr_iss_is_eretax(esr) && !kvm_auth_eretax(vcpu, &elr)) { /* - * Oh no, ERETAx failed to authenticate. If we have - * FPACCOMBINE, deliver an exception right away. If we - * don't, then let the mangled ELR value trickle down the + * Oh no, ERETAx failed to authenticate. + * + * If we have FPACCOMBINE and we don't have a pending + * Illegal Execution State exception (which has priority + * over FPAC), deliver an exception right away. + * + * Otherwise, let the mangled ELR value trickle down the * ERET handling, and the guest will have a little surprise. */ - if (kvm_has_pauth(vcpu->kvm, FPACCOMBINE)) { + if (kvm_has_pauth(vcpu->kvm, FPACCOMBINE) && !(spsr & PSR_IL_BIT)) { esr &= ESR_ELx_ERET_ISS_ERETA; esr |= FIELD_PREP(ESR_ELx_EC_MASK, ESR_ELx_EC_FPAC); kvm_inject_nested_sync(vcpu, esr); @@ -2201,17 +2208,11 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu) preempt_disable(); kvm_arch_vcpu_put(vcpu); - spsr = __vcpu_sys_reg(vcpu, SPSR_EL2); - spsr = kvm_check_illegal_exception_return(vcpu, spsr); if (!esr_iss_is_eretax(esr)) elr = __vcpu_sys_reg(vcpu, ELR_EL2); trace_kvm_nested_eret(vcpu, elr, spsr); - /* - * Note that the current exception level is always the virtual EL2, - * since we set HCR_EL2.NV bit only when entering the virtual EL2. - */ *vcpu_pc(vcpu) = elr; *vcpu_cpsr(vcpu) = spsr; -- cgit v1.2.3