Am Mon, Sep 26, 2022 at 11:31:29PM +0200 schrieb Jason A. Donenfeld:
> The full RNG initialization relies on some timestamps, made possible
> with general functions like time_init() and timekeeping_init(). However,
> these are only available rather late in initialization. Meanwhile, other
> things, such as memory allocator functions, make use of the RNG much
> earlier.
>
> So split RNG initialization into two phases. We can give arch randomness
> very early on, and then later, after timekeeping and such are available,
> initialize the rest.
>
> This ensures that, for example, slabs are properly randomized if RDRAND
> is available. Without this, CONFIG_SLAB_FREELIST_RANDOM=y loses a degree
> of its security, because its random seed is potentially deterministic,
> since it hasn't yet incorporated RDRAND. It also makes it possible to
> use a better seed in kfence, which currently relies on only the cycle
> counter.
>
> Another positive consequence is that on systems with RDRAND, running
> with CONFIG_WARN_ALL_UNSEEDED_RANDOM=y results in no warnings at all.
Nice improvement. One question, though:
> #if defined(LATENT_ENTROPY_PLUGIN)
> static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
> @@ -803,34 +798,46 @@ int __init random_init(const char *command_line)
> i += longs;
> continue;
> }
> - entropy[0] = random_get_entropy();
> - _mix_pool_bytes(entropy, sizeof(*entropy));
> arch_bits -= sizeof(*entropy) * 8;
> ++i;
> }
Previously, random_get_entropy() was mixed into the pool ARRAY_SIZE(entropy)
times.
> +/*
> + * This is called a little bit after the prior function, and now there is
> + * access to timestamps counters. Interrupts are not yet enabled.
> + */
> +void __init random_init(void)
> +{
> + unsigned long entropy = random_get_entropy();
> + ktime_t now = ktime_get_real();
> +
> + _mix_pool_bytes(utsname(), sizeof(*(utsname())));
But now, it's only mixed into the pool once. Is this change on purpose?
Thanks,
Dominik
