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    Subject[PATCH 4.19 126/234] random: mix build-time latent entropy into pool at init
    Date
    From: "Jason A. Donenfeld" <Jason@zx2c4.com>

    commit 1754abb3e7583c570666fa1e1ee5b317e88c89a0 upstream.

    Prior, the "input_pool_data" array needed no real initialization, and so
    it was easy to mark it with __latent_entropy to populate it during
    compile-time. In switching to using a hash function, this required us to
    specifically initialize it to some specific state, which means we
    dropped the __latent_entropy attribute. An unfortunate side effect was
    this meant the pool was no longer seeded using compile-time random data.
    In order to bring this back, we declare an array in rand_initialize()
    with __latent_entropy and call mix_pool_bytes() on that at init, which
    accomplishes the same thing as before. We make this __initconst, so that
    it doesn't take up space at runtime after init.

    Fixes: 6e8ec2552c7d ("random: use computational hash for entropy extraction")
    Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
    Reviewed-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -967,6 +967,11 @@ int __init rand_initialize(void)
    bool arch_init = true;
    unsigned long rv;

    +#if defined(LATENT_ENTROPY_PLUGIN)
    + static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
    + _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
    +#endif
    +
    for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
    if (!arch_get_random_seed_long_early(&rv) &&
    !arch_get_random_long_early(&rv)) {

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