Am Sonntag, 22. September 2013, 16:38:53 schrieb Theodore Ts'o:
Hi Theodore,
>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.
Are there any plans to get such function implemented on large list of
architectures without a get_cycles function?
Thanks
>
>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.
Ciao
Stephan
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