[RFC PATCH 09/25] KVM: arm64: Make ID_AA64ISAR1_EL1 writable

[Reiji Watanabe]

This patch adds id_reg_info for ID_AA64ISAR1_EL1 to make it
writable by userspace.

Return an error if userspace tries to set PTRAUTH related fields
of the register to values that conflict with PTRAUTH configuration
for the guest (via KVM_ARM_VCPU_INIT).

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 79 +++++++++++++++++++++++++++++++++++----
 1 file changed, 72 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 73b5dad0b2ee..7819a07ee248 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -263,6 +263,24 @@ static bool trap_raz_wi(struct kvm_vcpu *vcpu,
 		return read_zero(vcpu, p);
 }
 
+#define PTRAUTH_MASK	(ARM64_FEATURE_MASK(ID_AA64ISAR1_APA) |	\
+			 ARM64_FEATURE_MASK(ID_AA64ISAR1_API) | \
+			 ARM64_FEATURE_MASK(ID_AA64ISAR1_GPA) |	\
+			 ARM64_FEATURE_MASK(ID_AA64ISAR1_GPI))
+
+#define aa64isar1_has_apa(val)	\
+	(cpuid_feature_extract_unsigned_field(val, ID_AA64ISAR1_APA_SHIFT) >= \
+	 ID_AA64ISAR1_APA_ARCHITECTED)
+#define aa64isar1_has_api(val)	\
+	(cpuid_feature_extract_unsigned_field(val, ID_AA64ISAR1_API_SHIFT) >= \
+	 ID_AA64ISAR1_API_IMP_DEF)
+#define aa64isar1_has_gpa(val)	\
+	(cpuid_feature_extract_unsigned_field(val, ID_AA64ISAR1_GPA_SHIFT) >= \
+	 ID_AA64ISAR1_GPA_ARCHITECTED)
+#define aa64isar1_has_gpi(val)	\
+	(cpuid_feature_extract_unsigned_field(val, ID_AA64ISAR1_GPI_SHIFT) >= \
+	 ID_AA64ISAR1_GPI_IMP_DEF)
+
 struct id_reg_info {
 	u32	sys_reg;	/* Register ID */
 	u64	sys_val;	/* Sanitized system value */
@@ -353,6 +371,37 @@ static int validate_id_aa64isar0_el1(struct kvm_vcpu *vcpu, u64 val)
 	return 0;
 }
 
+static int validate_id_aa64isar1_el1(struct kvm_vcpu *vcpu, u64 val)
+{
+	unsigned int gpi, gpa, api, apa;
+	bool generic, address;
+	bool vcpu_ptrauth = vcpu_has_ptrauth(vcpu);
+
+	gpi = aa64isar1_has_gpi(val);
+	gpa = aa64isar1_has_gpa(val);
+	api = aa64isar1_has_api(val);
+	apa = aa64isar1_has_apa(val);
+	if ((gpi && gpa) || (api && apa))
+		return -EINVAL;
+
+	generic = gpi || gpa;
+	address = api || apa;
+
+	/*
+	 * Since the current KVM guest implementation works by enabling
+	 * both address/generic pointer authentication features,
+	 * return an error if they conflict.
+	 */
+	if (generic ^ address)
+		return -EPERM;
+
+	/* Check if there is a conflict with a request via KVM_ARM_VCPU_INIT */
+	if (vcpu_ptrauth ^ (generic && address))
+		return -EPERM;
+
+	return 0;
+}
+
 static void init_id_aa64pfr0_el1_info(struct id_reg_info *id_reg)
 {
 	u64 limit;
@@ -388,6 +437,14 @@ static void init_id_aa64pfr1_el1_info(struct id_reg_info *id_reg)
 		(id_reg->sys_val & ~ARM64_FEATURE_MASK(ID_AA64PFR1_MTE)));
 }
 
+static void init_id_aa64isar1_el1_info(struct id_reg_info *id_reg)
+{
+	id_reg->sys_val = read_sanitised_ftr_reg(id_reg->sys_reg);
+	id_reg->vcpu_limit_val = system_has_full_ptr_auth() ?
+				 id_reg->sys_val :
+				 (id_reg->sys_val & ~PTRAUTH_MASK);
+}
+
 static u64 get_reset_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 				     struct id_reg_info *idr)
 {
@@ -404,6 +461,13 @@ static u64 get_reset_id_aa64pfr1_el1(struct kvm_vcpu *vcpu,
 	       (idr->vcpu_limit_val & ~(ARM64_FEATURE_MASK(ID_AA64PFR1_MTE)));
 }
 
+static u64 get_reset_id_aa64isar1_el1(struct kvm_vcpu *vcpu,
+				      struct id_reg_info *idr)
+{
+	return vcpu_has_ptrauth(vcpu) ?
+	       idr->vcpu_limit_val : (idr->vcpu_limit_val & ~PTRAUTH_MASK);
+}
+
 static struct id_reg_info id_aa64pfr0_el1_info = {
 	.sys_reg = SYS_ID_AA64PFR0_EL1,
 	.init = init_id_aa64pfr0_el1_info,
@@ -426,6 +490,13 @@ static struct id_reg_info id_aa64isar0_el1_info = {
 	.validate = validate_id_aa64isar0_el1,
 };
 
+static struct id_reg_info id_aa64isar1_el1_info = {
+	.sys_reg = SYS_ID_AA64ISAR1_EL1,
+	.init = init_id_aa64isar1_el1_info,
+	.validate = validate_id_aa64isar1_el1,
+	.get_reset_val = get_reset_id_aa64isar1_el1,
+};
+
 /*
  * An ID register that needs special handling to control the value for the
  * guest must have its own id_reg_info in id_reg_info_table.
@@ -438,6 +509,7 @@ static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {
 	[IDREG_IDX(SYS_ID_AA64PFR0_EL1)] = &id_aa64pfr0_el1_info,
 	[IDREG_IDX(SYS_ID_AA64PFR1_EL1)] = &id_aa64pfr1_el1_info,
 	[IDREG_IDX(SYS_ID_AA64ISAR0_EL1)] = &id_aa64isar0_el1_info,
+	[IDREG_IDX(SYS_ID_AA64ISAR1_EL1)] = &id_aa64isar1_el1_info,
 };
 
 static int validate_id_reg(struct kvm_vcpu *vcpu,
@@ -1274,13 +1346,6 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 	u64 val = raz ? 0 : __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id));
 
 	switch (id) {
-	case SYS_ID_AA64ISAR1_EL1:
-		if (!vcpu_has_ptrauth(vcpu))
-			val &= ~(ARM64_FEATURE_MASK(ID_AA64ISAR1_APA) |
-				 ARM64_FEATURE_MASK(ID_AA64ISAR1_API) |
-				 ARM64_FEATURE_MASK(ID_AA64ISAR1_GPA) |
-				 ARM64_FEATURE_MASK(ID_AA64ISAR1_GPI));
-		break;
 	case SYS_ID_AA64DFR0_EL1:
 		/* Limit debug to ARMv8.0 */
 		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
-- 
2.33.0.882.g93a45727a2-goog