3.2.53-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Theodore Ts'o <ty...@mit.edu>
commit 61875f30daf60305712e25b209ef41ced2635bad upstream.
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>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
drivers/char/random.c | 8 ++++----
include/linux/timex.h | 14 ++++++++++++++
2 files changed, 18 insertions(+), 4 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -668,7 +668,7 @@ static void set_timer_rand_state(unsigne
*/
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);
@@ -705,7 +705,7 @@ static void add_timer_randomness(struct
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);
@@ -772,7 +772,7 @@ void add_interrupt_randomness(int irq, i
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;
@@ -1503,7 +1503,7 @@ 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);
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -173,6 +173,20 @@ struct timex {
#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.
--
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