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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
Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/char/random.c
View File

@@ -643,7 +643,7 @@ struct timer_rand_state {
*/ */
void add_device_randomness(const void *buf, unsigned int size) 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, buf, size, NULL);
mix_pool_bytes(&input_pool, &time, sizeof(time), 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; goto out;
sample.jiffies = jiffies; sample.jiffies = jiffies;
sample.cycles = get_cycles(); sample.cycles = random_get_entropy();
sample.num = num; sample.num = num;
mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL); 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 fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
struct pt_regs *regs = get_irq_regs(); struct pt_regs *regs = get_irq_regs();
unsigned long now = jiffies; unsigned long now = jiffies;
__u32 input[4], cycles = get_cycles(); __u32 input[4], cycles = random_get_entropy();
input[0] = cycles ^ jiffies; input[0] = cycles ^ jiffies;
input[1] = irq; input[1] = irq;
@@ -1485,7 +1485,7 @@ unsigned int get_random_int(void)
hash = get_cpu_var(get_random_int_hash); 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); md5_transform(hash, random_int_secret);
ret = hash[0]; ret = hash[0];
put_cpu_var(get_random_int_hash); put_cpu_var(get_random_int_hash);

14
include/linux/timex.h
View File

@@ -64,6 +64,20 @@
#include <asm/timex.h> #include <asm/timex.h>
#ifndef random_get_entropy
/*
* The random_get_entropy() function is used by the /dev/random driver
* in order to extract entropy via the relative unpredictability of
* when an interrupt takes places versus a high speed, fine-grained
* timing source or cycle counter. Since it will be occurred on every
* single interrupt, it must have a very low cost/overhead.
*
* By default we use get_cycles() for this purpose, but individual
* architectures may override this in their asm/timex.h header file.
*/
#define random_get_entropy() get_cycles()
#endif
/* /*
* SHIFT_PLL is used as a dampening factor to define how much we * SHIFT_PLL is used as a dampening factor to define how much we
* adjust the frequency correction for a given offset in PLL mode. * adjust the frequency correction for a given offset in PLL mode.