[PATCH v6 2/6] KVM: arm64: Reject attempts to set invalid debug arch version

[Jing Zhang]

From: Oliver Upton <oliver.upton at 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.

Signed-off-by: Oliver Upton <oliver.upton at linux.dev>
Signed-off-by: Jing Zhang <jingzhangos at google.com>
---
 arch/arm64/kvm/sys_regs.c | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c1a5ec1a016e..053d8057ff1e 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1216,8 +1216,14 @@ static s64 kvm_arm64_ftr_safe_value(u32 id, const struct arm64_ftr_bits *ftrp,
 	/* Some features have different safe value type in KVM than host features */
 	switch (id) {
 	case SYS_ID_AA64DFR0_EL1:
-		if (kvm_ftr.shift == ID_AA64DFR0_EL1_PMUVer_SHIFT)
+		switch (kvm_ftr.shift) {
+		case ID_AA64DFR0_EL1_PMUVer_SHIFT:
 			kvm_ftr.type = FTR_LOWER_SAFE;
+			break;
+		case ID_AA64DFR0_EL1_DebugVer_SHIFT:
+			kvm_ftr.type = FTR_LOWER_SAFE;
+			break;
+		}
 		break;
 	case SYS_ID_DFR0_EL1:
 		if (kvm_ftr.shift == ID_DFR0_EL1_PerfMon_SHIFT)
@@ -1469,14 +1475,22 @@ static u64 read_sanitised_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 	return val;
 }
 
+#define ID_REG_LIMIT_FIELD_ENUM(val, reg, field, limit)			       \
+({									       \
+	u64 __f_val = FIELD_GET(reg##_##field##_MASK, val);		       \
+	(val) &= ~reg##_##field##_MASK;					       \
+	(val) |= FIELD_PREP(reg##_##field##_MASK,			       \
+			min(__f_val, (u64)reg##_##field##_##limit));	       \
+	(val);								       \
+})
+
 static u64 read_sanitised_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 					  const struct sys_reg_desc *rd)
 {
 	u64 val = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
 
 	/* Limit debug to ARMv8.0 */
-	val &= ~ID_AA64DFR0_EL1_DebugVer_MASK;
-	val |= SYS_FIELD_PREP_ENUM(ID_AA64DFR0_EL1, DebugVer, IMP);
+	val = ID_REG_LIMIT_FIELD_ENUM(val, ID_AA64DFR0_EL1, DebugVer, V8P8);
 
 	/*
 	 * Only initialize the PMU version if the vCPU was configured with one.
@@ -1496,6 +1510,7 @@ 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);
 
 	/*
@@ -1515,6 +1530,13 @@ 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);
 }
 
@@ -1528,6 +1550,8 @@ static u64 read_sanitised_id_dfr0_el1(struct kvm_vcpu *vcpu,
 	if (kvm_vcpu_has_pmu(vcpu))
 		val |= SYS_FIELD_PREP(ID_DFR0_EL1, PerfMon, perfmon);
 
+	val = ID_REG_LIMIT_FIELD_ENUM(val, ID_DFR0_EL1, CopDbg, Debugv8p8);
+
 	return val;
 }
 
@@ -1536,6 +1560,7 @@ 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;
@@ -1551,6 +1576,9 @@ 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);
 }
 
-- 
2.41.0.255.g8b1d071c50-goog