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: "Theodore Ts'o" <tytso@mit.edu> Cc: stable@vger.kernel.org
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@ -643,7 +643,7 @@ struct timer_rand_state {
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*/
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void add_device_randomness(const void *buf, unsigned int size)
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{
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unsigned long time = get_cycles() ^ jiffies;
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unsigned long time = random_get_entropy() ^ jiffies;
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mix_pool_bytes(&input_pool, buf, size, NULL);
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mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
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@ -680,7 +680,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
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goto out;
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sample.jiffies = jiffies;
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sample.cycles = get_cycles();
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sample.cycles = random_get_entropy();
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sample.num = num;
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mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
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@ -747,7 +747,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
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struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
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struct pt_regs *regs = get_irq_regs();
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unsigned long now = jiffies;
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__u32 input[4], cycles = get_cycles();
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__u32 input[4], cycles = random_get_entropy();
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input[0] = cycles ^ jiffies;
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input[1] = irq;
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@ -1485,7 +1485,7 @@ unsigned int get_random_int(void)
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hash = get_cpu_var(get_random_int_hash);
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hash[0] += current->pid + jiffies + get_cycles();
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hash[0] += current->pid + jiffies + random_get_entropy();
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md5_transform(hash, random_int_secret);
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ret = hash[0];
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put_cpu_var(get_random_int_hash);
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@ -64,6 +64,20 @@
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#include <asm/timex.h>
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#ifndef random_get_entropy
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/*
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* The random_get_entropy() function is used by the /dev/random driver
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* in order to extract entropy via the relative unpredictability of
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* when an interrupt takes places versus a high speed, fine-grained
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* timing source or cycle counter. Since it will be occurred on every
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* single interrupt, it must have a very low cost/overhead.
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*
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* By default we use get_cycles() for this purpose, but individual
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* architectures may override this in their asm/timex.h header file.
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*/
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#define random_get_entropy() get_cycles()
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#endif
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/*
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* SHIFT_PLL is used as a dampening factor to define how much we
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* adjust the frequency correction for a given offset in PLL mode.
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