[PATCH] KVM: arm64: Reject attempts to set invalid debug arch version

[Oliver Upton <oliver.upton@linux.dev>]

The debug architecture is mandatory in ARMv8, so KVM should not allow
userspace to configure a vCPU with less than that. Of course, this isn't
handled elegantly by the generic ID register plumbing, as the respective
ID register fields have a nonzero starting value.

Add an explicit check for debug versions less than v8 of the
architecture.

Fixes: c118cead07a7 ("KVM: arm64: Use generic sanitisation for ID_(AA64)DFR0_EL1")
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/sys_regs.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1a13bab1a06c..5b25053a8e04 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1482,6 +1482,7 @@ static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 			       const struct sys_reg_desc *rd,
 			       u64 val)
 {
+	u8 debugver = SYS_FIELD_GET(ID_AA64DFR0_EL1, DebugVer, val);
 	u8 pmuver = SYS_FIELD_GET(ID_AA64DFR0_EL1, PMUVer, val);
 
 	/*
@@ -1501,6 +1502,13 @@ static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 	if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
 		val &= ~ID_AA64DFR0_EL1_PMUVer_MASK;
 
+	/*
+	 * ID_AA64DFR0_EL1.DebugVer is one of those awkward fields with a
+	 * nonzero minimum safe value.
+	 */
+	if (debugver < ID_AA64DFR0_EL1_DebugVer_IMP)
+		return -EINVAL;
+
 	return set_id_reg(vcpu, rd, val);
 }
 
@@ -1522,6 +1530,7 @@ static int set_id_dfr0_el1(struct kvm_vcpu *vcpu,
 			   u64 val)
 {
 	u8 perfmon = SYS_FIELD_GET(ID_DFR0_EL1, PerfMon, val);
+	u8 copdbg = SYS_FIELD_GET(ID_DFR0_EL1, CopDbg, val);
 
 	if (perfmon == ID_DFR0_EL1_PerfMon_IMPDEF) {
 		val &= ~ID_DFR0_EL1_PerfMon_MASK;
@@ -1537,6 +1546,9 @@ static int set_id_dfr0_el1(struct kvm_vcpu *vcpu,
 	if (perfmon != 0 && perfmon < ID_DFR0_EL1_PerfMon_PMUv3)
 		return -EINVAL;
 
+	if (copdbg < ID_DFR0_EL1_CopDbg_Armv8)
+		return -EINVAL;
+
 	return set_id_reg(vcpu, rd, val);
 }
 

base-commit: 192df2aa0113ddddee2a93e453ff46610807b425
-- 
2.41.0.178.g377b9f9a00-goog