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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_ARCHRANDOM_H
#define _ASM_ARCHRANDOM_H
#include <linux/arm-smccc.h>
#include <linux/bug.h>
#include <linux/kernel.h>
#include <linux/irqflags.h>
#include <asm/cpufeature.h>
#define ARM_SMCCC_TRNG_MIN_VERSION 0x10000UL
extern bool smccc_trng_available;
static inline bool __init smccc_probe_trng(void)
{
struct arm_smccc_res res;
arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res);
if ((s32)res.a0 < 0)
return false;
return res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION;
}
static inline bool __arm64_rndr(unsigned long *v)
{
bool ok;
/*
* 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");
return ok;
}
static inline bool __arm64_rndrrs(unsigned long *v)
{
bool ok;
/*
* 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");
return ok;
}
static __always_inline bool __cpu_has_rng(void)
{
if (unlikely(!system_capabilities_finalized() && !preemptible()))
return this_cpu_has_cap(ARM64_HAS_RNG);
return alternative_has_cap_unlikely(ARM64_HAS_RNG);
}
static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
{
/*
* Only support the generic interface after we have detected
* the system wide capability, avoiding complexity with the
* cpufeature code and with potential scheduling between CPUs
* with and without the feature.
*/
if (max_longs && __cpu_has_rng() && __arm64_rndr(v))
return 1;
return 0;
}
static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
{
if (!max_longs)
return 0;
/*
* We prefer the SMCCC call, since its semantics (return actual
* hardware backed entropy) is closer to the idea behind this
* function here than what even the RNDRSS register provides
* (the output of a pseudo RNG freshly seeded by a TRNG).
*/
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;
}
}
/*
* RNDRRS is not backed by an entropy source but by a DRBG that is
* reseeded after each invocation. This is not a 100% fit but good
* enough to implement this API if no other entropy source exists.
*/
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;
}
#endif /* _ASM_ARCHRANDOM_H */
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