linux-kernel - [PATCH v9 09/39] arm64/cpufeature: Runtime detection of Guarded Control Stack (GCS)

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Date: Tue, 25 Jun 2024 15:57:37 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>, 
 Andrew Morton <akpm@...ux-foundation.org>, Marc Zyngier <maz@...nel.org>, 
 Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, Arnd Bergmann <arnd@...db.de>, 
 Oleg Nesterov <oleg@...hat.com>, Eric Biederman <ebiederm@...ssion.com>, 
 Shuah Khan <shuah@...nel.org>, 
 "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>, 
 Deepak Gupta <debug@...osinc.com>, Ard Biesheuvel <ardb@...nel.org>, 
 Szabolcs Nagy <Szabolcs.Nagy@....com>, Kees Cook <kees@...nel.org>
Cc: "H.J. Lu" <hjl.tools@...il.com>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Florian Weimer <fweimer@...hat.com>, Christian Brauner <brauner@...nel.org>, 
 Thiago Jung Bauermann <thiago.bauermann@...aro.org>, 
 Ross Burton <ross.burton@....com>, linux-arm-kernel@...ts.infradead.org, 
 linux-doc@...r.kernel.org, kvmarm@...ts.linux.dev, 
 linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org, 
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH v9 09/39] arm64/cpufeature: Runtime detection of Guarded
 Control Stack (GCS)

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

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
Signed-off-by: Mark Brown <broonie@...nel.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 8b904a757bd3..0ebed5dfe55f 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 48e7029f1054..056d394920f9 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),
@@ -2347,6 +2349,12 @@ 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)
@@ -2869,6 +2877,14 @@ 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,
+		.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 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