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Commit 61875f30 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: allow architectures to optionally define random_get_entropy() 



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: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent 47d06e53

drivers/char/random.c

+4 −4
Original line number Diff line number Diff line
@@ -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);

include/linux/timex.h

+14 −0
Original line number Diff line number Diff line
@@ -64,6 +64,20 @@ 


#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

 * adjust the frequency correction for a given offset in PLL mode.