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Subject[ 34/44] random: mix in architectural randomness in extract_buf()
Date
From: Greg KH <gregkh@linuxfoundation.org>

3.0-stable review patch. If anyone has any objections, please let me know.

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

From: "H. Peter Anvin" <hpa@linux.intel.com>

commit d2e7c96af1e54b507ae2a6a7dd2baf588417a7e5 upstream.

Mix in any architectural randomness in extract_buf() instead of
xfer_secondary_buf(). This allows us to mix in more architectural
randomness, and it also makes xfer_secondary_buf() faster, moving a
tiny bit of additional CPU overhead to process which is extracting the
randomness.

[ Commit description modified by tytso to remove an extended
advertisement for the RDRAND instruction. ]

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: DJ Johnston <dj.johnston@intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/char/random.c | 56 ++++++++++++++++++++++++++++----------------------
1 file changed, 32 insertions(+), 24 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -277,6 +277,8 @@
#define SEC_XFER_SIZE 512
#define EXTRACT_SIZE 10

+#define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
+
/*
* The minimum number of bits of entropy before we wake up a read on
* /dev/random. Should be enough to do a significant reseed.
@@ -813,11 +815,7 @@ static ssize_t extract_entropy(struct en
*/
static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
{
- union {
- __u32 tmp[OUTPUT_POOL_WORDS];
- long hwrand[4];
- } u;
- int i;
+ __u32 tmp[OUTPUT_POOL_WORDS];

if (r->pull && r->entropy_count < nbytes * 8 &&
r->entropy_count < r->poolinfo->POOLBITS) {
@@ -828,23 +826,17 @@ static void xfer_secondary_pool(struct e
/* pull at least as many as BYTES as wakeup BITS */
bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
/* but never more than the buffer size */
- bytes = min_t(int, bytes, sizeof(u.tmp));
+ bytes = min_t(int, bytes, sizeof(tmp));

DEBUG_ENT("going to reseed %s with %d bits "
"(%d of %d requested)\n",
r->name, bytes * 8, nbytes * 8, r->entropy_count);

- bytes = extract_entropy(r->pull, u.tmp, bytes,
+ bytes = extract_entropy(r->pull, tmp, bytes,
random_read_wakeup_thresh / 8, rsvd);
- mix_pool_bytes(r, u.tmp, bytes, NULL);
+ mix_pool_bytes(r, tmp, bytes, NULL);
credit_entropy_bits(r, bytes*8);
}
- kmemcheck_mark_initialized(&u.hwrand, sizeof(u.hwrand));
- for (i = 0; i < 4; i++)
- if (arch_get_random_long(&u.hwrand[i]))
- break;
- if (i)
- mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
}

/*
@@ -901,15 +893,19 @@ static size_t account(struct entropy_sto
static void extract_buf(struct entropy_store *r, __u8 *out)
{
int i;
- __u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
+ union {
+ __u32 w[5];
+ unsigned long l[LONGS(EXTRACT_SIZE)];
+ } hash;
+ __u32 workspace[SHA_WORKSPACE_WORDS];
__u8 extract[64];
unsigned long flags;

/* Generate a hash across the pool, 16 words (512 bits) at a time */
- sha_init(hash);
+ sha_init(hash.w);
spin_lock_irqsave(&r->lock, flags);
for (i = 0; i < r->poolinfo->poolwords; i += 16)
- sha_transform(hash, (__u8 *)(r->pool + i), workspace);
+ sha_transform(hash.w, (__u8 *)(r->pool + i), workspace);

/*
* We mix the hash back into the pool to prevent backtracking
@@ -920,14 +916,14 @@ static void extract_buf(struct entropy_s
* brute-forcing the feedback as hard as brute-forcing the
* hash.
*/
- __mix_pool_bytes(r, hash, sizeof(hash), extract);
+ __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract);
spin_unlock_irqrestore(&r->lock, flags);

/*
* To avoid duplicates, we atomically extract a portion of the
* pool while mixing, and hash one final time.
*/
- sha_transform(hash, extract, workspace);
+ sha_transform(hash.w, extract, workspace);
memset(extract, 0, sizeof(extract));
memset(workspace, 0, sizeof(workspace));

@@ -936,11 +932,23 @@ static void extract_buf(struct entropy_s
* pattern, we fold it in half. Thus, we always feed back
* twice as much data as we output.
*/
- hash[0] ^= hash[3];
- hash[1] ^= hash[4];
- hash[2] ^= rol32(hash[2], 16);
- memcpy(out, hash, EXTRACT_SIZE);
- memset(hash, 0, sizeof(hash));
+ hash.w[0] ^= hash.w[3];
+ hash.w[1] ^= hash.w[4];
+ hash.w[2] ^= rol32(hash.w[2], 16);
+
+ /*
+ * If we have a architectural hardware random number
+ * generator, mix that in, too.
+ */
+ for (i = 0; i < LONGS(EXTRACT_SIZE); i++) {
+ unsigned long v;
+ if (!arch_get_random_long(&v))
+ break;
+ hash.l[i] ^= v;
+ }
+
+ memcpy(out, &hash, EXTRACT_SIZE);
+ memset(&hash, 0, sizeof(hash));
}

static ssize_t extract_entropy(struct entropy_store *r, void *buf,



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