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KVM: arm64: Clear HCR_EL2.RW for 32-bit non-protected vCPUs

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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: b56680de9c ("KVM: arm64: Initialize trap register values in hyp in pKVM")
Cc: stable@vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20260929090031.3829185-3-fuad.tabba@linux.dev
Signed-off-by: Oliver Upton <oupton@kernel.org>
This commit is contained in:
Fuad Tabba 2026-09-29 10:00:29 +01:00 committed by Oliver Upton
parent 4bdd2b3a70
commit 80ae56184b
1 changed files with 9 additions and 0 deletions
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9
arch/arm64/kvm/hyp/nvhe/pkvm.c
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@ -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);