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    Subject[ 163/180] random: Use arch_get_random_int instead of cycle counter if avail
    2.6.32-longterm review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Linus Torvalds <torvalds@linux-foundation.org>

    commit cf833d0b9937874b50ef2867c4e8badfd64948ce upstream.

    We still don't use rdrand in /dev/random, which just seems stupid. We
    accept the *cycle*counter* as a random input, but we don't accept
    rdrand? That's just broken.

    Sure, people can do things in user space (write to /dev/random, use
    rdrand in addition to /dev/random themselves etc etc), but that
    *still* seems to be a particularly stupid reason for saying "we
    shouldn't bother to try to do better in /dev/random".

    And even if somebody really doesn't trust rdrand as a source of random
    bytes, it seems singularly stupid to trust the cycle counter *more*.

    So I'd suggest the attached patch. I'm not going to even bother
    arguing that we should add more bits to the entropy estimate, because
    that's not the point - I don't care if /dev/random fills up slowly or
    not, I think it's just stupid to not use the bits we can get from
    rdrand and mix them into the strong randomness pool.

    Link: http://lkml.kernel.org/r/CA%2B55aFwn59N1=m651QAyTy-1gO1noGbK18zwKDwvwqnravA84A@mail.gmail.com
    Acked-by: "David S. Miller" <davem@davemloft.net>
    Acked-by: "Theodore Ts'o" <tytso@mit.edu>
    Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
    Cc: Matt Mackall <mpm@selenic.com>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    ---
    drivers/char/random.c | 8 ++++++--
    1 files changed, 6 insertions(+), 2 deletions(-)

    diff --git a/drivers/char/random.c b/drivers/char/random.c
    index f2a1651..ac74029 100644
    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -624,8 +624,8 @@ static struct timer_rand_state input_timer_state;
    static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
    {
    struct {
    - cycles_t cycles;
    long jiffies;
    + unsigned cycles;
    unsigned num;
    } sample;
    long delta, delta2, delta3;
    @@ -637,7 +637,11 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
    goto out;

    sample.jiffies = jiffies;
    - sample.cycles = get_cycles();
    +
    + /* Use arch random value, fall back to cycles */
    + if (!arch_get_random_int(&sample.cycles))
    + sample.cycles = get_cycles();
    +
    sample.num = num;
    mix_pool_bytes(&input_pool, &sample, sizeof(sample));

    --
    1.7.2.1.45.g54fbc




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