On Wed, 6 Nov 2019 at 15:20, Richard Henderson
<richard.henderson@xxxxxxxxxx> wrote:
>
> 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.
> ---
> 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 | 79 +++++++++++++++++++
> arch/arm64/Kconfig | 12 +++
> arch/arm64/kernel/Makefile | 1 +
> drivers/char/Kconfig | 4 +-
> 9 files changed, 150 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..a13f082d88e6
> --- /dev/null
> +++ b/arch/arm64/kernel/random.c
> @@ -0,0 +1,79 @@
> +/* 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-preemptable context, current cpu has RNG.
> + * Case 1 is the expected case when RNG is deployed, but
> + * case 2 is present as a backup in case some big/little
> + * system only has RNG on big cpus, we can still add entropy
> + * from the interrupt handler of the big cpus.
I don't understand the reference to the interrupt handler here. It is
worth mentioning though that this arrangement permits
rand_initialize() to use the instructions regardless of whether they
are implemented only by the boot CPU or by all of them.
> + * 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
>
