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" <ty...@mit.edu> --- drivers/char/random.c | 8 ++++---- include/linux/timex.h | 17 +++++++++++++++++ 2 files changed, 21 insertions(+), 4 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 9564144..ba23d5c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -707,7 +707,7 @@ 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; unsigned long flags; trace_add_device_randomness(size, _RET_IP_); @@ -751,7 +751,7 @@ 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); @@ -818,7 +818,7 @@ 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; @@ -1580,7 +1580,7 @@ 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); diff --git a/include/linux/timex.h b/include/linux/timex.h index b3726e6..f9780cc 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -64,6 +64,23 @@ #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. + */ +static inline cycles_t random_get_entropy(void) +{ + return 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. -- 1.7.12.rc0.22.gcdd159b -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/