[PATCH v8 09/38] arm64/cpufeature: Runtime detection of Guarded Control Stack (GCS)

Mark Brown
2024-02-03T12:30:30Z

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

Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/cpufeature.h | 6 ++++++
arch/arm64/kernel/cpufeature.c | 16 ++++++++++++++++
arch/arm64/tools/cpucaps | 1 +
3 files changed, 23 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 21c824edf8ce..3f3a685fa6e2 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -825,6 +825,12 @@ 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 8d1a634a403e..b606842ab8c1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -255,6 +255,8 @@ 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),
@@ -2250,6 +2252,12 @@ static void cpu_enable_mops(const struct arm64_cpu_capabilities *__unused)
sysreg_clear_set(sctlr_el1, 0, SCTLR_EL1_MSCEn);
}

+static void cpu_enable_gcs(const struct arm64_cpu_capabilities *__unused)
+{
+ /* GCS is not currently used at EL1 */
+ write_sysreg_s(0, SYS_GCSCR_EL1);
+}
+
/* Internal helper functions to match cpu capability type */
static bool
cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
@@ -2739,6 +2747,14 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.type = ARM64_CPUCAP_SYSTEM_FEATURE,
.matches = has_lpa2,
},
+ {
+ .desc = "Guarded Control Stack (GCS)",
+ .capability = ARM64_HAS_GCS,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .cpu_enable = cpu_enable_gcs,
+ .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 b912b1409fc0..148734504295 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -28,6 +28,7 @@ HAS_EPAN
HAS_EVT
HAS_FGT
HAS_FPSIMD
+HAS_GCS
HAS_GENERIC_AUTH
HAS_GENERIC_AUTH_ARCH_QARMA3
HAS_GENERIC_AUTH_ARCH_QARMA5

--
2.30.2