[PATCH v5 29/39] arm64: Add helpers to probe local CPU for PAC and BTI support

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb at kernel.org>

Add some helpers that will be used by the early kernel mapping code to
check feature support on the local CPU. This permits the early kernel
mapping to be created with the right attributes, removing the need for
tearing it down and recreating it.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/include/asm/cpufeature.h | 44 ++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 99c01417e544..301d4d2211d5 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -921,6 +921,50 @@ static inline bool kaslr_disabled_cmdline(void)
 u32 get_kvm_ipa_limit(void);
 void dump_cpu_features(void);
 
+static inline bool cpu_has_bti(void)
+{
+	u64 pfr1;
+
+	if (!IS_ENABLED(CONFIG_ARM64_BTI))
+		return false;
+
+	pfr1 = read_cpuid(ID_AA64PFR1_EL1);
+	pfr1 &= ~id_aa64pfr1_override.mask;
+	pfr1 |= id_aa64pfr1_override.val;
+
+	return cpuid_feature_extract_unsigned_field(pfr1,
+						    ID_AA64PFR1_EL1_BT_SHIFT);
+}
+
+static inline bool cpu_has_pac(void)
+{
+	u64 isar1, isar2;
+	u8 feat;
+
+	if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH))
+		return false;
+
+	isar1 = read_cpuid(ID_AA64ISAR1_EL1);
+	isar1 &= ~id_aa64isar1_override.mask;
+	isar1 |= id_aa64isar1_override.val;
+	feat = cpuid_feature_extract_unsigned_field(isar1,
+						    ID_AA64ISAR1_EL1_APA_SHIFT);
+	if (feat)
+		return true;
+
+	feat = cpuid_feature_extract_unsigned_field(isar1,
+						    ID_AA64ISAR1_EL1_API_SHIFT);
+	if (feat)
+		return true;
+
+	isar2 = read_sysreg_s(SYS_ID_AA64ISAR2_EL1);
+	isar2 &= ~id_aa64isar2_override.mask;
+	isar2 |= id_aa64isar2_override.val;
+	feat = cpuid_feature_extract_unsigned_field(isar2,
+						    ID_AA64ISAR2_EL1_APA3_SHIFT);
+	return feat;
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif
-- 
2.43.0.rc1.413.gea7ed67945-goog