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random: allow architectures to optionally define random_get_entropy()

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Allow architectures which have a disabled get_cycles() function to
provide a random_get_entropy() function which provides a fine-grained,
rapidly changing counter that can be used by the /dev/random driver.

For example, an architecture might have a rapidly changing register
used to control random TLB cache eviction, or DRAM refresh that
doesn't meet the requirements of get_cycles(), but which is good
enough for the needs of the random driver.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
This commit is contained in:
Theodore Ts'o
2013-09-21 13:58:22 -04:00
parent 47d06e532e
commit 61875f30da
2 changed files with 18 additions and 4 deletions
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drivers/char/random.c
+4 -4
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@@ -643,7 +643,7 @@ struct timer_rand_state {
*/
void add_device_randomness(const void *buf, unsigned int size)
{
unsigned long time = get_cycles() ^ jiffies;
unsigned long time = random_get_entropy() ^ jiffies;
mix_pool_bytes(&input_pool, buf, size, NULL);
mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
@@ -680,7 +680,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
goto out;
sample.jiffies = jiffies;
sample.cycles = get_cycles();
sample.cycles = random_get_entropy();
sample.num = num;
mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
@@ -747,7 +747,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
struct pt_regs *regs = get_irq_regs();
unsigned long now = jiffies;
__u32 input[4], cycles = get_cycles();
__u32 input[4], cycles = random_get_entropy();
input[0] = cycles ^ jiffies;
input[1] = irq;
@@ -1485,7 +1485,7 @@ unsigned int get_random_int(void)
hash = get_cpu_var(get_random_int_hash);
hash[0] += current->pid + jiffies + get_cycles();
hash[0] += current->pid + jiffies + random_get_entropy();
md5_transform(hash, random_int_secret);
ret = hash[0];
put_cpu_var(get_random_int_hash);