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    Subject[PATCH 5.10 405/563] random: do not throw away excess input to crng_fast_load
    Date
    From: Jason A. Donenfeld <Jason@zx2c4.com>

    [ Upstream commit 73c7733f122e8d0107f88655a12011f68f69e74b ]

    When crng_fast_load() is called by add_hwgenerator_randomness(), we
    currently will advance to crng_init==1 once we've acquired 64 bytes, and
    then throw away the rest of the buffer. Usually, that is not a problem:
    When add_hwgenerator_randomness() gets called via EFI or DT during
    setup_arch(), there won't be any IRQ randomness. Therefore, the 64 bytes
    passed by EFI exactly matches what is needed to advance to crng_init==1.
    Usually, DT seems to pass 64 bytes as well -- with one notable exception
    being kexec, which hands over 128 bytes of entropy to the kexec'd kernel.
    In that case, we'll advance to crng_init==1 once 64 of those bytes are
    consumed by crng_fast_load(), but won't continue onward feeding in bytes
    to progress to crng_init==2. This commit fixes the issue by feeding
    any leftover bytes into the next phase in add_hwgenerator_randomness().

    [linux@dominikbrodowski.net: rewrite commit message]
    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/char/random.c | 19 ++++++++++++-------
    1 file changed, 12 insertions(+), 7 deletions(-)

    diff --git a/drivers/char/random.c b/drivers/char/random.c
    index 8c94380e7a463..5444206f35e22 100644
    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -922,12 +922,14 @@ static struct crng_state *select_crng(void)

    /*
    * crng_fast_load() can be called by code in the interrupt service
    - * path. So we can't afford to dilly-dally.
    + * path. So we can't afford to dilly-dally. Returns the number of
    + * bytes processed from cp.
    */
    -static int crng_fast_load(const char *cp, size_t len)
    +static size_t crng_fast_load(const char *cp, size_t len)
    {
    unsigned long flags;
    char *p;
    + size_t ret = 0;

    if (!spin_trylock_irqsave(&primary_crng.lock, flags))
    return 0;
    @@ -938,7 +940,7 @@ static int crng_fast_load(const char *cp, size_t len)
    p = (unsigned char *) &primary_crng.state[4];
    while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {
    p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp;
    - cp++; crng_init_cnt++; len--;
    + cp++; crng_init_cnt++; len--; ret++;
    }
    spin_unlock_irqrestore(&primary_crng.lock, flags);
    if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
    @@ -946,7 +948,7 @@ static int crng_fast_load(const char *cp, size_t len)
    crng_init = 1;
    pr_notice("fast init done\n");
    }
    - return 1;
    + return ret;
    }

    /*
    @@ -1299,7 +1301,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
    if (unlikely(crng_init == 0)) {
    if ((fast_pool->count >= 64) &&
    crng_fast_load((char *) fast_pool->pool,
    - sizeof(fast_pool->pool))) {
    + sizeof(fast_pool->pool)) > 0) {
    fast_pool->count = 0;
    fast_pool->last = now;
    }
    @@ -2319,8 +2321,11 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
    struct entropy_store *poolp = &input_pool;

    if (unlikely(crng_init == 0)) {
    - crng_fast_load(buffer, count);
    - return;
    + size_t ret = crng_fast_load(buffer, count);
    + count -= ret;
    + buffer += ret;
    + if (!count || crng_init == 0)
    + return;
    }

    /* Suspend writing if we're above the trickle threshold.
    --
    2.34.1


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