random: use lockless techniques in the interrupt path
The real-time Linux folks don't like add_interrupt_randomness() taking a spinlock since it is called in the low-level interrupt routine. This also allows us to reduce the overhead in the fast path, for the random driver, which is the interrupt collection path. Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Cc: stable@vger.kernel.org
This commit is contained in:
Theodore Ts'o
Родитель
775f4b297b
Коммит
902c098a36
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@ -418,9 +418,9 @@ struct entropy_store {
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/* read-write data: */
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spinlock_t lock;
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unsigned add_ptr;
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unsigned input_rotate;
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int entropy_count;
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int entropy_total;
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int input_rotate;
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unsigned int initialized:1;
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__u8 last_data[EXTRACT_SIZE];
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};
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@ -468,26 +468,24 @@ static __u32 const twist_table[8] = {
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* it's cheap to do so and helps slightly in the expected case where
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* the entropy is concentrated in the low-order bits.
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*/
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static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
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int nbytes, __u8 out[64])
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static void __mix_pool_bytes(struct entropy_store *r, const void *in,
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int nbytes, __u8 out[64])
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{
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unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
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int input_rotate;
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int wordmask = r->poolinfo->poolwords - 1;
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const char *bytes = in;
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__u32 w;
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unsigned long flags;
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/* Taps are constant, so we can load them without holding r->lock. */
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tap1 = r->poolinfo->tap1;
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tap2 = r->poolinfo->tap2;
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tap3 = r->poolinfo->tap3;
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tap4 = r->poolinfo->tap4;
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tap5 = r->poolinfo->tap5;
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spin_lock_irqsave(&r->lock, flags);
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input_rotate = r->input_rotate;
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i = r->add_ptr;
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smp_rmb();
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input_rotate = ACCESS_ONCE(r->input_rotate);
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i = ACCESS_ONCE(r->add_ptr);
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/* mix one byte at a time to simplify size handling and churn faster */
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while (nbytes--) {
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@ -514,19 +512,23 @@ static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
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input_rotate += i ? 7 : 14;
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}
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r->input_rotate = input_rotate;
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r->add_ptr = i;
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ACCESS_ONCE(r->input_rotate) = input_rotate;
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ACCESS_ONCE(r->add_ptr) = i;
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smp_wmb();
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if (out)
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for (j = 0; j < 16; j++)
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((__u32 *)out)[j] = r->pool[(i - j) & wordmask];
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spin_unlock_irqrestore(&r->lock, flags);
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}
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static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)
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static void mix_pool_bytes(struct entropy_store *r, const void *in,
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int nbytes, __u8 out[64])
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{
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mix_pool_bytes_extract(r, in, bytes, NULL);
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unsigned long flags;
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spin_lock_irqsave(&r->lock, flags);
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__mix_pool_bytes(r, in, nbytes, out);
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spin_unlock_irqrestore(&r->lock, flags);
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}
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struct fast_pool {
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@ -564,23 +566,22 @@ static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
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*/
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static void credit_entropy_bits(struct entropy_store *r, int nbits)
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{
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unsigned long flags;
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int entropy_count;
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int entropy_count, orig;
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if (!nbits)
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return;
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spin_lock_irqsave(&r->lock, flags);
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DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
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entropy_count = r->entropy_count;
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retry:
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entropy_count = orig = ACCESS_ONCE(r->entropy_count);
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entropy_count += nbits;
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if (entropy_count < 0) {
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DEBUG_ENT("negative entropy/overflow\n");
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entropy_count = 0;
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} else if (entropy_count > r->poolinfo->POOLBITS)
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entropy_count = r->poolinfo->POOLBITS;
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r->entropy_count = entropy_count;
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if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
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goto retry;
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if (!r->initialized && nbits > 0) {
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r->entropy_total += nbits;
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@ -593,7 +594,6 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
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wake_up_interruptible(&random_read_wait);
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kill_fasync(&fasync, SIGIO, POLL_IN);
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}
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spin_unlock_irqrestore(&r->lock, flags);
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}
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/*********************************************************************
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@ -680,7 +680,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
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sample.cycles = get_cycles();
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sample.num = num;
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mix_pool_bytes(&input_pool, &sample, sizeof(sample));
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mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
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/*
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* Calculate number of bits of randomness we probably added.
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@ -764,7 +764,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
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fast_pool->last = now;
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r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
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mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool));
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__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
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/*
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* If we don't have a valid cycle counter, and we see
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* back-to-back timer interrupts, then skip giving credit for
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@ -829,7 +829,7 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
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bytes = extract_entropy(r->pull, tmp, bytes,
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random_read_wakeup_thresh / 8, rsvd);
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mix_pool_bytes(r, tmp, bytes);
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mix_pool_bytes(r, tmp, bytes, NULL);
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credit_entropy_bits(r, bytes*8);
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}
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}
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@ -890,9 +890,11 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
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int i;
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__u32 hash[5], workspace[SHA_WORKSPACE_WORDS];
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__u8 extract[64];
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unsigned long flags;
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/* Generate a hash across the pool, 16 words (512 bits) at a time */
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sha_init(hash);
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spin_lock_irqsave(&r->lock, flags);
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for (i = 0; i < r->poolinfo->poolwords; i += 16)
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sha_transform(hash, (__u8 *)(r->pool + i), workspace);
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@ -905,7 +907,8 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
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* brute-forcing the feedback as hard as brute-forcing the
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* hash.
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*/
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mix_pool_bytes_extract(r, hash, sizeof(hash), extract);
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__mix_pool_bytes(r, hash, sizeof(hash), extract);
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spin_unlock_irqrestore(&r->lock, flags);
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/*
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* To avoid duplicates, we atomically extract a portion of the
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@ -928,11 +931,10 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
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}
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static ssize_t extract_entropy(struct entropy_store *r, void *buf,
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size_t nbytes, int min, int reserved)
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size_t nbytes, int min, int reserved)
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{
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ssize_t ret = 0, i;
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__u8 tmp[EXTRACT_SIZE];
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unsigned long flags;
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xfer_secondary_pool(r, nbytes);
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nbytes = account(r, nbytes, min, reserved);
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@ -941,6 +943,8 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
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extract_buf(r, tmp);
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if (fips_enabled) {
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unsigned long flags;
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spin_lock_irqsave(&r->lock, flags);
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if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
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panic("Hardware RNG duplicated output!\n");
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@ -1034,22 +1038,18 @@ EXPORT_SYMBOL(get_random_bytes);
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static void init_std_data(struct entropy_store *r)
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{
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int i;
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ktime_t now;
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unsigned long flags;
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ktime_t now = ktime_get_real();
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unsigned long rv;
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spin_lock_irqsave(&r->lock, flags);
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r->entropy_count = 0;
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r->entropy_total = 0;
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spin_unlock_irqrestore(&r->lock, flags);
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now = ktime_get_real();
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mix_pool_bytes(r, &now, sizeof(now));
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for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof flags) {
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if (!arch_get_random_long(&flags))
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mix_pool_bytes(r, &now, sizeof(now), NULL);
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for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
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if (!arch_get_random_long(&rv))
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break;
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mix_pool_bytes(r, &flags, sizeof(flags));
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mix_pool_bytes(r, &rv, sizeof(rv), NULL);
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}
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mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
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mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL);
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}
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static int rand_initialize(void)
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@ -1186,7 +1186,7 @@ write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
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count -= bytes;
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p += bytes;
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mix_pool_bytes(r, buf, bytes);
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mix_pool_bytes(r, buf, bytes, NULL);
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cond_resched();
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}
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