random: remove early archrandom abstraction
Commit Message
The arch_get_random*_early() abstraction is not completely useful and
adds complexity, because it's not a given that there will be no calls to
arch_get_random*() between random_init_early(), which uses
arch_get_random*_early(), and init_cpu_features(). During that gap,
crng_reseed() might be called, which uses arch_get_random*(), since it's
mostly not init code.
Instead we can test whether we're in the early phase in
arch_get_random*() itself, and in doing so avoid all ambiguity about
where we are. Fortunately, the only architecture that currently
implements arch_get_random*_early() also has an alternatives-based cpu
feature system, one flag of which determines whether the other flags
have been initialized. This makes it possible to do the early check with
zero cost once the system is initialized.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
Catalin - Though this touches arm64's archrandom.h, I intend to take
this through the random.git tree, if that's okay. I have other patches
that will build off of this one. -Jason
arch/arm64/include/asm/archrandom.h | 57 ++++++-----------------------
drivers/char/random.c | 4 +-
include/linux/random.h | 20 ----------
3 files changed, 14 insertions(+), 67 deletions(-)
Comments
On Sat, Oct 29, 2022 at 01:40:25AM +0200, Jason A. Donenfeld wrote:
> diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
> index 109e2a4454be..8a059a9033af 100644
> --- a/arch/arm64/include/asm/archrandom.h
> +++ b/arch/arm64/include/asm/archrandom.h
> @@ -58,6 +58,16 @@ static inline bool __arm64_rndrrs(unsigned long *v)
> return ok;
> }
>
> +static __always_inline bool __cpu_has_rng(void)
> +{
> + if (!system_capabilities_finalized()) {
> + /* Open code as we run prior to the first call to cpufeature. */
> + unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
> + return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
> + }
> + return cpus_have_const_cap(ARM64_HAS_RNG);
> +}
We need to be careful with this check as it is only valid on the CPU it
was called on. Is the result used only on this CPU and with the
preemption disabled? We have big.LITTLE systems where CPUs may differ
and the ARM64_HAS_RNG feature may not be enabled once all the CPUs have
been initialised (capabilities finalised).
We could make this capability an ARM64_CPUCAP_BOOT_CPU_FEATURE, though
I'd have to check whether any systems in the wild have such mixed CPUs.
Hi Catalin,
> > +static __always_inline bool __cpu_has_rng(void)
> > +{
> > + if (!system_capabilities_finalized()) {
> > + /* Open code as we run prior to the first call to cpufeature. */
> > + unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
> > + return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
> > + }
> > + return cpus_have_const_cap(ARM64_HAS_RNG);
> > +}
>
> We need to be careful with this check as it is only valid on the CPU it
> was called on. Is the result used only on this CPU and with the
> preemption disabled? We have big.LITTLE systems where CPUs may differ
> and the ARM64_HAS_RNG feature may not be enabled once all the CPUs have
> been initialised (capabilities finalised).
>
> We could make this capability an ARM64_CPUCAP_BOOT_CPU_FEATURE, though
> I'd have to check whether any systems in the wild have such mixed CPUs.
This occurred to me too and I wasn't quite sure how the interaction
worked out. It sounds like system_capabilities_finalized() might still
be false when SMP brings up other cores? In that case, I guess we just
have to make sure the system is still booting / in single CPU mode,
before interrupts have been enabled. This should be straight forward to
do; I'll send a v2.
Jason
@@ -58,6 +58,16 @@ static inline bool __arm64_rndrrs(unsigned long *v)
return ok;
}
+static __always_inline bool __cpu_has_rng(void)
+{
+ if (!system_capabilities_finalized()) {
+ /* Open code as we run prior to the first call to cpufeature. */
+ unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
+ return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
+ }
+ return cpus_have_const_cap(ARM64_HAS_RNG);
+}
+
static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
{
/*
@@ -66,7 +76,7 @@ static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t
* cpufeature code and with potential scheduling between CPUs
* with and without the feature.
*/
- if (max_longs && cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v))
+ if (max_longs && __cpu_has_rng() && __arm64_rndr(v))
return 1;
return 0;
}
@@ -108,53 +118,10 @@ static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, s
* reseeded after each invocation. This is not a 100% fit but good
* enough to implement this API if no other entropy source exists.
*/
- if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndrrs(v))
+ if (__cpu_has_rng() && __arm64_rndrrs(v))
return 1;
return 0;
}
-static inline bool __init __early_cpu_has_rndr(void)
-{
- /* Open code as we run prior to the first call to cpufeature. */
- unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
- return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
-}
-
-static inline size_t __init __must_check
-arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs)
-{
- WARN_ON(system_state != SYSTEM_BOOTING);
-
- if (!max_longs)
- return 0;
-
- if (smccc_trng_available) {
- struct arm_smccc_res res;
-
- max_longs = min_t(size_t, 3, max_longs);
- arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res);
- if ((int)res.a0 >= 0) {
- switch (max_longs) {
- case 3:
- *v++ = res.a1;
- fallthrough;
- case 2:
- *v++ = res.a2;
- fallthrough;
- case 1:
- *v++ = res.a3;
- break;
- }
- return max_longs;
- }
- }
-
- if (__early_cpu_has_rndr() && __arm64_rndr(v))
- return 1;
-
- return 0;
-}
-#define arch_get_random_seed_longs_early arch_get_random_seed_longs_early
-
#endif /* _ASM_ARCHRANDOM_H */
@@ -813,13 +813,13 @@ void __init random_init_early(const char *command_line)
#endif
for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
- longs = arch_get_random_seed_longs_early(entropy, ARRAY_SIZE(entropy) - i);
+ longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
if (longs) {
_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
i += longs;
continue;
}
- longs = arch_get_random_longs_early(entropy, ARRAY_SIZE(entropy) - i);
+ longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
if (longs) {
_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
i += longs;
@@ -153,26 +153,6 @@ declare_get_random_var_wait(long, unsigned long)
#include <asm/archrandom.h>
-/*
- * Called from the boot CPU during startup; not valid to call once
- * secondary CPUs are up and preemption is possible.
- */
-#ifndef arch_get_random_seed_longs_early
-static inline size_t __init arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs)
-{
- WARN_ON(system_state != SYSTEM_BOOTING);
- return arch_get_random_seed_longs(v, max_longs);
-}
-#endif
-
-#ifndef arch_get_random_longs_early
-static inline bool __init arch_get_random_longs_early(unsigned long *v, size_t max_longs)
-{
- WARN_ON(system_state != SYSTEM_BOOTING);
- return arch_get_random_longs(v, max_longs);
-}
-#endif
-
#ifdef CONFIG_SMP
int random_prepare_cpu(unsigned int cpu);
int random_online_cpu(unsigned int cpu);