[PATCH v10 10/40] arm64/cpufeature: Runtime detection of Guarded Control Stack (GCS)

[Mark Brown]

Add a cpufeature for GCS, allowing other code to conditionally support it
at runtime.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann at linaro.org>
Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/include/asm/cpufeature.h | 6 ++++++
 arch/arm64/kernel/cpufeature.c      | 9 +++++++++
 arch/arm64/tools/cpucaps            | 1 +
 3 files changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 558434267271..e0f0e4c24544 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -832,6 +832,12 @@ static inline bool system_supports_lpa2(void)
 	return cpus_have_final_cap(ARM64_HAS_LPA2);
 }
 
+static inline bool system_supports_gcs(void)
+{
+	return IS_ENABLED(CONFIG_ARM64_GCS) &&
+		alternative_has_cap_unlikely(ARM64_HAS_GCS);
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 646ecd3069fd..315bd7be1106 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -291,6 +291,8 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr1[] = {
+	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_GCS),
+		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_GCS_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SME),
 		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_SME_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR1_EL1_MPAM_frac_SHIFT, 4, 0),
@@ -2870,6 +2872,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = has_nv1,
 		ARM64_CPUID_FIELDS_NEG(ID_AA64MMFR4_EL1, E2H0, NI_NV1)
 	},
+	{
+		.desc = "Guarded Control Stack (GCS)",
+		.capability = ARM64_HAS_GCS,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_cpuid_feature,
+		ARM64_CPUID_FIELDS(ID_AA64PFR1_EL1, GCS, IMP)
+	},
 	{},
 };
 
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index ac3429d892b9..66eff95c0824 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -29,6 +29,7 @@ HAS_EVT
 HAS_FPMR
 HAS_FGT
 HAS_FPSIMD
+HAS_GCS
 HAS_GENERIC_AUTH
 HAS_GENERIC_AUTH_ARCH_QARMA3
 HAS_GENERIC_AUTH_ARCH_QARMA5

-- 
2.39.2