From: Richard Henderson <richard.henderson@xxxxxxxxxx>
Expose the ID_AA64ISAR0.RNDR field to userspace, as the
RNG system registers are always available at EL0.
Signed-off-by: Richard Henderson <richard.henderson@xxxxxxxxxx>
---
v2: Use __mrs_s and fix missing cc clobber (Mark),
Log rng failures with pr_warn (Mark),
Use __must_check; put RNDR in arch_get_random_long and RNDRRS
in arch_get_random_seed_long (Ard),
Use ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, and check this_cpu_has_cap
when reading random data. Move everything out of line, now that
there are 5 other function calls involved, and to unify the rate
limiting on the pr_warn.
v3: Keep arch_get_random{,_seed}_long in sync.
v4: Use __cpus_have_const_cap before falling back to this_cpu_has_cap.
v5: Improve commentary; fix some checkpatch warnings.
---
Documentation/arm64/cpu-feature-registers.rst | 2 +
arch/arm64/include/asm/archrandom.h | 35 ++++++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/sysreg.h | 4 +
arch/arm64/kernel/cpufeature.c | 13 +++
arch/arm64/kernel/random.c | 82 +++++++++++++++++++
arch/arm64/Kconfig | 12 +++
arch/arm64/kernel/Makefile | 1 +
drivers/char/Kconfig | 4 +-
9 files changed, 153 insertions(+), 3 deletions(-)
create mode 100644 arch/arm64/include/asm/archrandom.h
create mode 100644 arch/arm64/kernel/random.c
diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
index 2955287e9acc..78d6f5c6e824 100644
--- a/Documentation/arm64/cpu-feature-registers.rst
+++ b/Documentation/arm64/cpu-feature-registers.rst
@@ -117,6 +117,8 @@ infrastructure:
+------------------------------+---------+---------+
| Name | bits | visible |
+------------------------------+---------+---------+
+ | RNDR | [63-60] | y |
+ +------------------------------+---------+---------+
| TS | [55-52] | y |
+------------------------------+---------+---------+
| FHM | [51-48] | y |
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
new file mode 100644
index 000000000000..e796a6de7421
--- /dev/null
+++ b/arch/arm64/include/asm/archrandom.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARCHRANDOM_H
+#define _ASM_ARCHRANDOM_H
+
+#ifdef CONFIG_ARCH_RANDOM
+
+bool __must_check arch_get_random_long(unsigned long *v);
+bool __must_check arch_get_random_seed_long(unsigned long *v);
+
+static inline bool __must_check arch_get_random_int(unsigned int *v)
+{
+ unsigned long val;
+
+ if (arch_get_random_long(&val)) {
+ *v = val;
+ return true;
+ }
+
+ return false;
+}
+
+static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+{
+ unsigned long val;
+
+ if (arch_get_random_seed_long(&val)) {
+ *v = val;
+ return true;
+ }
+
+ return false;
+}
+
+#endif /* CONFIG_ARCH_RANDOM */
+#endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index ac1dbca3d0cd..1dd7644bc59a 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -54,7 +54,8 @@
#define ARM64_WORKAROUND_1463225 44
#define ARM64_WORKAROUND_CAVIUM_TX2_219_TVM 45
#define ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM 46
+#define ARM64_HAS_RNG 47
-#define ARM64_NCAPS 47
+#define ARM64_NCAPS 48
#endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 6e919fafb43d..5e718f279469 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -365,6 +365,9 @@
#define SYS_CTR_EL0 sys_reg(3, 3, 0, 0, 1)
#define SYS_DCZID_EL0 sys_reg(3, 3, 0, 0, 7)
+#define SYS_RNDR_EL0 sys_reg(3, 3, 2, 4, 0)
+#define SYS_RNDRRS_EL0 sys_reg(3, 3, 2, 4, 1)
+
#define SYS_PMCR_EL0 sys_reg(3, 3, 9, 12, 0)
#define SYS_PMCNTENSET_EL0 sys_reg(3, 3, 9, 12, 1)
#define SYS_PMCNTENCLR_EL0 sys_reg(3, 3, 9, 12, 2)
@@ -539,6 +542,7 @@
ENDIAN_SET_EL1 | SCTLR_EL1_UCI | SCTLR_EL1_RES1)
/* id_aa64isar0 */
+#define ID_AA64ISAR0_RNDR_SHIFT 60
#define ID_AA64ISAR0_TS_SHIFT 52
#define ID_AA64ISAR0_FHM_SHIFT 48
#define ID_AA64ISAR0_DP_SHIFT 44
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 80f459ad0190..456d5c461cbf 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -119,6 +119,7 @@ static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);
* sync with the documentation of the CPU feature register ABI.
*/
static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
+ ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_RNDR_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_TS_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_FHM_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_DP_SHIFT, 4, 0),
@@ -1565,6 +1566,18 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.sign = FTR_UNSIGNED,
.min_field_value = 1,
},
+#endif
+#ifdef CONFIG_ARCH_RANDOM
+ {
+ .desc = "Random Number Generator",
+ .capability = ARM64_HAS_RNG,
+ .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
+ .matches = has_cpuid_feature,
+ .sys_reg = SYS_ID_AA64ISAR0_EL1,
+ .field_pos = ID_AA64ISAR0_RNDR_SHIFT,
+ .sign = FTR_UNSIGNED,
+ .min_field_value = 1,
+ },
#endif
{},
};
diff --git a/arch/arm64/kernel/random.c b/arch/arm64/kernel/random.c
new file mode 100644
index 000000000000..e7ff29dd637c
--- /dev/null
+++ b/arch/arm64/kernel/random.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Random number generation using ARMv8.5-RNG.
+ */
+
+#include <linux/random.h>
+#include <linux/ratelimit.h>
+#include <linux/printk.h>
+#include <linux/preempt.h>
+#include <asm/cpufeature.h>
+
+static inline bool has_random(void)
+{
+ /*
+ * We "have" RNG if either
+ * (1) every cpu in the system has RNG, or
+ * (2) in a non-preemptible context, current cpu has RNG.
+ *
+ * Case 1 is the expected case when RNG is deployed, but
+ * case 2 is present as a backup. Case 2 has two effects:
+ * (A) rand_initialize() is able to use the instructions
+ * when present in the boot cpu, which happens before
+ * secondary cpus are enabled and before features are
+ * resolved for the full system.
+ * (B) add_interrupt_randomness() is able to use the
+ * instructions when present on the current cpu, in case
+ * some big/little system only has RNG on big cpus.
+ *
+ * We can use __cpus_have_const_cap because we then fall
+ * back to checking the current cpu.
+ */
+ return __cpus_have_const_cap(ARM64_HAS_RNG) ||
+ (!preemptible() && this_cpu_has_cap(ARM64_HAS_RNG));
+}
+
+bool arch_get_random_long(unsigned long *v)
+{
+ bool ok;
+
+ if (!has_random())
+ return false;
+
+ /*
+ * Reads of RNDR set PSTATE.NZCV to 0b0000 on success,
+ * and set PSTATE.NZCV to 0b0100 otherwise.
+ */
+ asm volatile(
+ __mrs_s("%0", SYS_RNDR_EL0) "\n"
+ " cset %w1, ne\n"
+ : "=r"(*v), "=r"(ok)
+ :
+ : "cc");
+
+ if (unlikely(!ok))
+ pr_warn_ratelimited("cpu%d: sys_rndr failed\n",
+ read_cpuid_id());
+ return ok;
+}
+
+bool arch_get_random_seed_long(unsigned long *v)
+{
+ bool ok;
+
+ if (!has_random())
+ return false;
+
+ /*
+ * Reads of RNDRRS set PSTATE.NZCV to 0b0000 on success,
+ * and set PSTATE.NZCV to 0b0100 otherwise.
+ */
+ asm volatile(
+ __mrs_s("%0", SYS_RNDRRS_EL0) "\n"
+ " cset %w1, ne\n"
+ : "=r"(*v), "=r"(ok)
+ :
+ : "cc");
+
+ if (unlikely(!ok))
+ pr_warn_ratelimited("cpu%d: sys_rndrrs failed\n",
+ read_cpuid_id());
+ return ok;
+}
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3f047afb982c..5bc88601f07b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1438,6 +1438,18 @@ config ARM64_PTR_AUTH
endmenu
+menu "ARMv8.5 architectural features"
+
+config ARCH_RANDOM
+ bool "Enable support for random number generation"
+ default y
+ help
+ Random number generation (part of the ARMv8.5 Extensions)
+ provides a high bandwidth, cryptographically secure
+ hardware random number generator.
+
+endmenu
+
config ARM64_SVE
bool "ARM Scalable Vector Extension support"
default y
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 478491f07b4f..a47c2b984da7 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o
obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
obj-$(CONFIG_ARM64_SSBD) += ssbd.o
obj-$(CONFIG_ARM64_PTR_AUTH) += pointer_auth.o
+obj-$(CONFIG_ARCH_RANDOM) += random.o
obj-y += vdso/ probes/
obj-$(CONFIG_COMPAT_VDSO) += vdso32/
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index df0fc997dc3e..f26a0a8cc0d0 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -539,7 +539,7 @@ endmenu
config RANDOM_TRUST_CPU
bool "Trust the CPU manufacturer to initialize Linux's CRNG"
- depends on X86 || S390 || PPC
+ depends on X86 || S390 || PPC || ARM64
default n
help
Assume that CPU manufacturer (e.g., Intel or AMD for RDSEED or
@@ -559,4 +559,4 @@ config RANDOM_TRUST_BOOTLOADER
device randomness. Say Y here to assume the entropy provided by the
booloader is trustworthy so it will be added to the kernel's entropy
pool. Otherwise, say N here so it will be regarded as device input that
- only mixes the entropy pool.
\ No newline at end of file
+ only mixes the entropy pool.
--
2.17.1
