arm64/hwcap: Add hwcap for GCS

Provide a hwcap to enable userspace to detect support for GCS.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Link: https://lore.kernel.org/r/20241001-arm64-gcs-v13-18-222b78d87eee@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: broonie

Documentation/arch/arm64/elf_hwcaps.rst

@@ -170,6 +170,10 @@ HWCAP_PACG
     ID_AA64ISAR1_EL1.GPI == 0b0001, as described by
     Documentation/arch/arm64/pointer-authentication.rst.
 
+HWCAP_GCS
+    Functionality implied by ID_AA64PFR1_EL1.GCS == 0b1, as
+    described by Documentation/arch/arm64/gcs.rst.
+
 HWCAP2_DCPODP
     Functionality implied by ID_AA64ISAR1_EL1.DPB == 0b0010.
 

arch/arm64/include/asm/hwcap.h

@@ -92,6 +92,7 @@
 #define KERNEL_HWCAP_SB			__khwcap_feature(SB)
 #define KERNEL_HWCAP_PACA		__khwcap_feature(PACA)
 #define KERNEL_HWCAP_PACG		__khwcap_feature(PACG)
+#define KERNEL_HWCAP_GCS		__khwcap_feature(GCS)
 
 #define __khwcap2_feature(x)		(const_ilog2(HWCAP2_ ## x) + 64)
 #define KERNEL_HWCAP_DCPODP		__khwcap2_feature(DCPODP)

arch/arm64/include/uapi/asm/hwcap.h

@@ -21,7 +21,7 @@
  * HWCAP flags - for AT_HWCAP
  *
  * Bits 62 and 63 are reserved for use by libc.
- * Bits 32-61 are unallocated for potential use by libc.
+ * Bits 33-61 are unallocated for potential use by libc.
  */
 #define HWCAP_FP		(1 << 0)
 #define HWCAP_ASIMD		(1 << 1)
@@ -55,6 +55,7 @@
 #define HWCAP_SB		(1 << 29)
 #define HWCAP_PACA		(1 << 30)
 #define HWCAP_PACG		(1UL << 31)
+#define HWCAP_GCS		(1UL << 32)
 
 /*
  * HWCAP2 flags - for AT_HWCAP2

arch/arm64/kernel/cpufeature.c

@@ -3025,6 +3025,9 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64ZFR0_EL1, I8MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEI8MM),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, F32MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF32MM),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, F64MM, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEF64MM),
+#endif
+#ifdef CONFIG_ARM64_GCS
+	HWCAP_CAP(ID_AA64PFR1_EL1, GCS, IMP, CAP_HWCAP, KERNEL_HWCAP_GCS),
 #endif
 	HWCAP_CAP(ID_AA64PFR1_EL1, SSBS, SSBS2, CAP_HWCAP, KERNEL_HWCAP_SSBS),
 #ifdef CONFIG_ARM64_BTI

arch/arm64/kernel/cpuinfo.c

@@ -80,6 +80,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_SB]		= "sb",
 	[KERNEL_HWCAP_PACA]		= "paca",
 	[KERNEL_HWCAP_PACG]		= "pacg",
+	[KERNEL_HWCAP_GCS]		= "gcs",
 	[KERNEL_HWCAP_DCPODP]		= "dcpodp",
 	[KERNEL_HWCAP_SVE2]		= "sve2",
 	[KERNEL_HWCAP_SVEAES]		= "sveaes",