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From:   Sandy Harris <sandyinchina@gmail.com>
Date:   Thu, 9 Sep 2021 10:49:20 +0800
Message-ID: <CACXcFmm798P6mPErh9B4thz7uvBG1sUO-eJpa1MB+7ayDyTCvw@mail.gmail.com>
Subject: [PATCH] In _extract-crng mix in 64 bits if possible
To:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        "Ted Ts'o" <tytso@mit.edu>,
        Herbert Xu <herbert@gondor.apana.org.au>
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Precedence: bulk

On some machines arch_get_random_long() gives 64 bits.
XORing it into a 32-bit state word uses only half of it.
This change makes it use it all instead.

Signed-off-by: Sandy Harris <sandyinchina@gmail.com>

---
 drivers/char/random.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 57fe011fb5e4..fe7f3366b934 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -988,7 +988,8 @@ static void crng_reseed(struct crng_state *crng,
struct entropy_store *r)
 static void _extract_crng(struct crng_state *crng,
               __u8 out[CHACHA_BLOCK_SIZE])
 {
-    unsigned long v, flags;
+    unsigned long v, flags, *last;
+    last = (unsigned long *) &crng->state[14] ;

     if (crng_ready() &&
         (time_after(crng_global_init_time, crng->init_time) ||
@@ -996,7 +997,7 @@ static void _extract_crng(struct crng_state *crng,
         crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
     spin_lock_irqsave(&crng->lock, flags);
     if (arch_get_random_long(&v))
-        crng->state[14] ^= v;
+        *last ^= v;
     chacha20_block(&crng->state[0], out);
     if (crng->state[12] == 0)
         crng->state[13]++;
--