From 80ae56184b57176b908cd6a7ececf274a7e4b3c7 Mon Sep 17 00:00:00 2001 From: Fuad Tabba Date: Tue, 29 Sep 2026 10:00:29 +0100 Subject: [PATCH] KVM: arm64: Clear HCR_EL2.RW for 32-bit non-protected vCPUs pKVM keeps its own copy of each vCPU's HCR_EL2 at EL2, initialised with RW set unconditionally. Nothing stops userspace from creating a non-protected AArch32 VM, and with RW set, entering one of its vCPUs is an illegal exception return: KVM_RUN fails with KVM_EXIT_FAIL_ENTRY. Clear RW for a vCPU that is AArch32 at EL1, when the CPU has AArch32 EL1. On a CPU without it, RW stays set and the entry still fails, rather than EL2 switching *32_EL2 registers that are UNDEFINED there. The host already rejects such a vCPU, but EL2 takes the vCPU's features from the host and doesn't rely on that. Fixes: b56680de9c648 ("KVM: arm64: Initialize trap register values in hyp in pKVM") Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Link: https://patch.msgid.link/20260929090031.3829185-3-fuad.tabba@linux.dev Signed-off-by: Oliver Upton --- arch/arm64/kvm/hyp/nvhe/pkvm.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c index bb3e0dc0676e..cd09d8888202 100644 --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c @@ -54,6 +54,15 @@ static void pkvm_vcpu_reset_hcr(struct kvm_vcpu *vcpu) else vcpu->arch.hcr_el2 |= HCR_TID2; + /* + * Without AArch32 EL1, leave RW set and let the entry fail with an + * illegal exception return: the *32_EL2 registers EL2 would otherwise + * switch are UNDEFINED there. + */ + if (vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT) && + cpus_have_final_cap(ARM64_HAS_32BIT_EL1)) + vcpu->arch.hcr_el2 &= ~HCR_EL2_RW; + if (vcpu_has_ptrauth(vcpu)) vcpu->arch.hcr_el2 |= (HCR_API | HCR_APK);