Re: [PATCH v4 4/5] arm64: Add support for SMCCC TRNG entropy source
From: Mark Brown <broonie@kernel.org>
Date: 2020-12-11 17:31:59
Also in:
kvmarm, lkml
On Fri, Dec 11, 2020 at 04:00:04PM +0000, Andre Przywara wrote:
static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
{
+ struct arm_smccc_res res;
+
+ /*
+ * 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).
+ */This logic...
quoted hunk ↗ jump to hunk
@@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long *v) { WARN_ON(system_state != SYSTEM_BOOTING); - if (!__early_cpu_has_rndr()) - return false; + if (__early_cpu_has_rndr()) + return __arm64_rndr(v); + + if (smccc_trng_available) { + struct arm_smccc_res res; - return __arm64_rndr(v); + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res); + if ((int)res.a0 >= 0) { + *v = res.a3; + return true; + } + } + + return false;
...seems to also apply here but we prefer the RNDR instead of the SMCC. We probably want to either do the same thing or add a comment saying what's going on.