[RFC PATCH v3 26/29] KVM: arm64: Trap disabled features of ID_AA64ISAR1_EL1

[Reiji Watanabe]

Add feature_config_ctrl for PTRAUTH, which is indicated in
ID_AA64ISAR1_EL1, to program configuration register to trap
guest's using the feature when it is not exposed to the guest.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 3d3b29515b8b..f1f975ce7b07 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -376,6 +376,30 @@ static int arm64_check_features(u64 check_types, u64 val, u64 lim)
 	(cpuid_feature_extract_unsigned_field(val, ID_AA64ISAR1_GPI_SHIFT) >= \
 	 ID_AA64ISAR1_GPI_IMP_DEF)
 
+/*
+ * Return true if ptrauth needs to be trapped.
+ * (i.e. if ptrauth is supported on the host but not exposed to the guest)
+ */
+static bool vcpu_need_trap_ptrauth(struct kvm_vcpu *vcpu)
+{
+	u64 val;
+	bool generic, address;
+
+	if (!system_has_full_ptr_auth())
+		/* The feature is not supported. */
+		return false;
+
+	val = __read_id_reg(vcpu, SYS_ID_AA64ISAR1_EL1);
+	generic = aa64isar1_has_gpi(val) || aa64isar1_has_gpa(val);
+	address = aa64isar1_has_api(val) || aa64isar1_has_apa(val);
+	if (generic && address)
+		/* The feature is available. */
+		return false;
+
+	/* The feature is supported but hidden. */
+	return true;
+}
+
 enum vcpu_config_reg {
 	VCPU_HCR_EL2 = 1,
 	VCPU_MDCR_EL2,
@@ -480,6 +504,14 @@ static struct feature_config_ctrl ftr_ctrl_lor = {
 	.cfg_val = HCR_TLOR,
 };
 
+/* For SYS_ID_AA64ISAR1_EL1 */
+static struct feature_config_ctrl ftr_ctrl_ptrauth = {
+	.ftr_need_trap = vcpu_need_trap_ptrauth,
+	.cfg_reg = VCPU_HCR_EL2,
+	.cfg_mask = (HCR_API | HCR_APK),
+	.cfg_val = 0,
+};
+
 struct id_reg_info {
 	u32	sys_reg;	/* Register ID */
 	u64	sys_val;	/* Sanitized system value */
@@ -977,6 +1009,10 @@ static struct id_reg_info id_aa64isar1_el1_info = {
 	.init = init_id_aa64isar1_el1_info,
 	.validate = validate_id_aa64isar1_el1,
 	.get_reset_val = get_reset_id_aa64isar1_el1,
+	.trap_features = &(const struct feature_config_ctrl *[]) {
+		&ftr_ctrl_ptrauth,
+		NULL,
+	},
 };
 
 static struct id_reg_info id_aa64mmfr0_el1_info = {
-- 
2.34.0.rc1.387.gb447b232ab-goog