random: use RDSEED instead of RDRAND in entropy extraction
commit 28f425e573e906a4c15f8392cc2b1561ef448595 upstream. When /dev/random was directly connected with entropy extraction, without any expansion stage, extract_buf() was called for every 10 bytes of data read from /dev/random. For that reason, RDRAND was used rather than RDSEED. At the same time, crng_reseed() was still only called every 5 minutes, so there RDSEED made sense. Those olden days were also a time when the entropy collector did not use a cryptographic hash function, which meant most bets were off in terms of real preimage resistance. For that reason too it didn't matter _that_ much whether RDSEED was mixed in before or after entropy extraction; both choices were sort of bad. But now we have a cryptographic hash function at work, and with that we get real preimage resistance. We also now only call extract_entropy() every 5 minutes, rather than every 10 bytes. This allows us to do two important things. First, we can switch to using RDSEED in extract_entropy(), as Dominik suggested. Second, we can ensure that RDSEED input always goes into the cryptographic hash function with other things before being used directly. This eliminates a category of attacks in which the CPU knows the current state of the crng and knows that we're going to xor RDSEED into it, and so it computes a malicious RDSEED. By going through our hash function, it would require the CPU to compute a preimage on the fly, which isn't going to happen. Cc: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net> Suggested-by: Dominik Brodowski <linux@dominikbrodowski.net> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jason A. Donenfeld
Greg Kroah-Hartman
parent
9924c212e0
commit
a07ddc05f9
@ -324,14 +324,11 @@ static struct crng_state primary_crng = {
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* its value (from 0->1->2).
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*/
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static int crng_init = 0;
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static bool crng_need_final_init = false;
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#define crng_ready() (likely(crng_init > 1))
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static int crng_init_cnt = 0;
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static unsigned long crng_global_init_time = 0;
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#define CRNG_INIT_CNT_THRESH (2 * CHACHA20_KEY_SIZE)
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static void _extract_crng(struct crng_state *crng, u8 out[CHACHA20_BLOCK_SIZE]);
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static void _crng_backtrack_protect(struct crng_state *crng,
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u8 tmp[CHACHA20_BLOCK_SIZE], int used);
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static void extract_crng(u8 out[CHACHA20_BLOCK_SIZE]);
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static void crng_backtrack_protect(u8 tmp[CHACHA20_BLOCK_SIZE], int used);
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static void process_random_ready_list(void);
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static void _get_random_bytes(void *buf, int nbytes);
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@ -366,7 +363,7 @@ static struct {
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static void extract_entropy(void *buf, size_t nbytes);
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static void crng_reseed(struct crng_state *crng);
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static void crng_reseed(void);
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/*
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* This function adds bytes into the entropy "pool". It does not
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@ -465,7 +462,7 @@ static void credit_entropy_bits(int nbits)
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trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_);
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if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
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crng_reseed(&primary_crng);
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crng_reseed();
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}
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/*********************************************************************
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@ -478,14 +475,6 @@ static void credit_entropy_bits(int nbits)
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static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
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/*
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* Hack to deal with crazy userspace progams when they are all trying
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* to access /dev/urandom in parallel. The programs are almost
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* certainly doing something terribly wrong, but we'll work around
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* their brain damage.
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*/
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static struct crng_state **crng_node_pool __read_mostly;
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static void invalidate_batched_entropy(void);
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static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
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@ -495,24 +484,6 @@ static int __init parse_trust_cpu(char *arg)
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}
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early_param("random.trust_cpu", parse_trust_cpu);
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static bool crng_init_try_arch(struct crng_state *crng)
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{
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int i;
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bool arch_init = true;
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unsigned long rv;
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for (i = 4; i < 16; i++) {
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if (!arch_get_random_seed_long(&rv) &&
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!arch_get_random_long(&rv)) {
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rv = random_get_entropy();
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arch_init = false;
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}
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crng->state[i] ^= rv;
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}
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return arch_init;
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}
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static bool __init crng_init_try_arch_early(void)
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{
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int i;
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@ -531,100 +502,17 @@ static bool __init crng_init_try_arch_early(void)
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return arch_init;
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}
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static void crng_initialize_secondary(struct crng_state *crng)
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{
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chacha_init_consts(crng->state);
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_get_random_bytes(&crng->state[4], sizeof(u32) * 12);
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crng_init_try_arch(crng);
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crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
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}
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static void __init crng_initialize_primary(void)
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static void __init crng_initialize(void)
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{
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extract_entropy(&primary_crng.state[4], sizeof(u32) * 12);
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if (crng_init_try_arch_early() && trust_cpu && crng_init < 2) {
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invalidate_batched_entropy();
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numa_crng_init();
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crng_init = 2;
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pr_notice("crng init done (trusting CPU's manufacturer)\n");
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}
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primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
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}
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static void crng_finalize_init(void)
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{
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if (!system_wq) {
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/* We can't call numa_crng_init until we have workqueues,
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* so mark this for processing later. */
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crng_need_final_init = true;
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return;
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}
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invalidate_batched_entropy();
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numa_crng_init();
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crng_init = 2;
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crng_need_final_init = false;
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process_random_ready_list();
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wake_up_interruptible(&crng_init_wait);
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kill_fasync(&fasync, SIGIO, POLL_IN);
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pr_notice("crng init done\n");
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if (unseeded_warning.missed) {
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pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
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unseeded_warning.missed);
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unseeded_warning.missed = 0;
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}
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if (urandom_warning.missed) {
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pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
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urandom_warning.missed);
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urandom_warning.missed = 0;
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}
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}
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static void do_numa_crng_init(struct work_struct *work)
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{
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int i;
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struct crng_state *crng;
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struct crng_state **pool;
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pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL | __GFP_NOFAIL);
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for_each_online_node(i) {
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crng = kmalloc_node(sizeof(struct crng_state),
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GFP_KERNEL | __GFP_NOFAIL, i);
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spin_lock_init(&crng->lock);
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crng_initialize_secondary(crng);
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pool[i] = crng;
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}
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/* pairs with READ_ONCE() in select_crng() */
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if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) {
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for_each_node(i)
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kfree(pool[i]);
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kfree(pool);
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}
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}
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static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);
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static void numa_crng_init(void)
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{
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if (IS_ENABLED(CONFIG_NUMA))
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schedule_work(&numa_crng_init_work);
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}
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static struct crng_state *select_crng(void)
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{
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if (IS_ENABLED(CONFIG_NUMA)) {
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struct crng_state **pool;
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int nid = numa_node_id();
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/* pairs with cmpxchg_release() in do_numa_crng_init() */
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pool = READ_ONCE(crng_node_pool);
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if (pool && pool[nid])
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return pool[nid];
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}
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return &primary_crng;
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}
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/*
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* crng_fast_load() can be called by code in the interrupt service
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* path. So we can't afford to dilly-dally. Returns the number of
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@ -753,73 +641,71 @@ static int crng_slow_load(const u8 *cp, size_t len)
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return 1;
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}
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static void crng_reseed(struct crng_state *crng)
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static void crng_reseed(void)
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{
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unsigned long flags;
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int i;
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int i, entropy_count;
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union {
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u8 block[CHACHA20_BLOCK_SIZE];
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u32 key[8];
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} buf;
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if (crng == &primary_crng) {
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int entropy_count;
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do {
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entropy_count = READ_ONCE(input_pool.entropy_count);
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if (entropy_count < POOL_MIN_BITS)
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return;
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} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
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extract_entropy(buf.key, sizeof(buf.key));
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wake_up_interruptible(&random_write_wait);
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kill_fasync(&fasync, SIGIO, POLL_OUT);
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} else {
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_extract_crng(&primary_crng, buf.block);
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_crng_backtrack_protect(&primary_crng, buf.block,
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CHACHA20_KEY_SIZE);
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}
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spin_lock_irqsave(&crng->lock, flags);
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for (i = 0; i < 8; i++) {
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unsigned long rv;
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if (!arch_get_random_seed_long(&rv) &&
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!arch_get_random_long(&rv))
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rv = random_get_entropy();
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crng->state[i + 4] ^= buf.key[i] ^ rv;
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}
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do {
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entropy_count = READ_ONCE(input_pool.entropy_count);
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if (entropy_count < POOL_MIN_BITS)
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return;
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} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
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extract_entropy(buf.key, sizeof(buf.key));
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wake_up_interruptible(&random_write_wait);
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kill_fasync(&fasync, SIGIO, POLL_OUT);
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spin_lock_irqsave(&primary_crng.lock, flags);
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for (i = 0; i < 8; i++)
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primary_crng.state[i + 4] ^= buf.key[i];
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memzero_explicit(&buf, sizeof(buf));
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WRITE_ONCE(crng->init_time, jiffies);
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spin_unlock_irqrestore(&crng->lock, flags);
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if (crng == &primary_crng && crng_init < 2)
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crng_finalize_init();
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}
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static void _extract_crng(struct crng_state *crng, u8 out[CHACHA20_BLOCK_SIZE])
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{
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unsigned long flags, init_time;
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if (crng_ready()) {
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init_time = READ_ONCE(crng->init_time);
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if (time_after(READ_ONCE(crng_global_init_time), init_time) ||
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time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))
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crng_reseed(crng);
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WRITE_ONCE(primary_crng.init_time, jiffies);
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spin_unlock_irqrestore(&primary_crng.lock, flags);
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if (crng_init < 2) {
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invalidate_batched_entropy();
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crng_init = 2;
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process_random_ready_list();
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wake_up_interruptible(&crng_init_wait);
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kill_fasync(&fasync, SIGIO, POLL_IN);
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pr_notice("crng init done\n");
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if (unseeded_warning.missed) {
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pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
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unseeded_warning.missed);
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unseeded_warning.missed = 0;
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}
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if (urandom_warning.missed) {
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pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
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urandom_warning.missed);
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urandom_warning.missed = 0;
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}
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}
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spin_lock_irqsave(&crng->lock, flags);
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chacha20_block(&crng->state[0], out);
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if (crng->state[12] == 0)
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crng->state[13]++;
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spin_unlock_irqrestore(&crng->lock, flags);
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}
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static void extract_crng(u8 out[CHACHA20_BLOCK_SIZE])
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{
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_extract_crng(select_crng(), out);
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unsigned long flags, init_time;
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if (crng_ready()) {
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init_time = READ_ONCE(primary_crng.init_time);
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if (time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))
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crng_reseed();
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}
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spin_lock_irqsave(&primary_crng.lock, flags);
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chacha20_block(&primary_crng.state[0], out);
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if (primary_crng.state[12] == 0)
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primary_crng.state[13]++;
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spin_unlock_irqrestore(&primary_crng.lock, flags);
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}
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/*
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* Use the leftover bytes from the CRNG block output (if there is
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* enough) to mutate the CRNG key to provide backtracking protection.
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*/
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static void _crng_backtrack_protect(struct crng_state *crng,
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u8 tmp[CHACHA20_BLOCK_SIZE], int used)
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static void crng_backtrack_protect(u8 tmp[CHACHA20_BLOCK_SIZE], int used)
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{
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unsigned long flags;
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u32 *s, *d;
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@ -830,17 +716,12 @@ static void _crng_backtrack_protect(struct crng_state *crng,
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extract_crng(tmp);
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used = 0;
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}
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spin_lock_irqsave(&crng->lock, flags);
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spin_lock_irqsave(&primary_crng.lock, flags);
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s = (u32 *)&tmp[used];
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d = &crng->state[4];
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d = &primary_crng.state[4];
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for (i = 0; i < 8; i++)
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*d++ ^= *s++;
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spin_unlock_irqrestore(&crng->lock, flags);
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}
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static void crng_backtrack_protect(u8 tmp[CHACHA20_BLOCK_SIZE], int used)
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{
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_crng_backtrack_protect(select_crng(), tmp, used);
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spin_unlock_irqrestore(&primary_crng.lock, flags);
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}
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static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
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@ -1105,16 +986,17 @@ static void extract_entropy(void *buf, size_t nbytes)
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unsigned long flags;
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u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
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struct {
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unsigned long rdrand[32 / sizeof(long)];
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unsigned long rdseed[32 / sizeof(long)];
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size_t counter;
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} block;
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size_t i;
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trace_extract_entropy(nbytes, input_pool.entropy_count);
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for (i = 0; i < ARRAY_SIZE(block.rdrand); ++i) {
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if (!arch_get_random_long(&block.rdrand[i]))
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block.rdrand[i] = random_get_entropy();
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for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
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if (!arch_get_random_seed_long(&block.rdseed[i]) &&
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!arch_get_random_long(&block.rdseed[i]))
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block.rdseed[i] = random_get_entropy();
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}
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spin_lock_irqsave(&input_pool.lock, flags);
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@ -1122,7 +1004,7 @@ static void extract_entropy(void *buf, size_t nbytes)
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/* seed = HASHPRF(last_key, entropy_input) */
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blake2s_final(&input_pool.hash, seed);
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/* next_key = HASHPRF(seed, RDRAND || 0) */
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/* next_key = HASHPRF(seed, RDSEED || 0) */
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block.counter = 0;
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blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
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blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
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@ -1132,7 +1014,7 @@ static void extract_entropy(void *buf, size_t nbytes)
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while (nbytes) {
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i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
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/* output = HASHPRF(seed, RDRAND || ++counter) */
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/* output = HASHPRF(seed, RDSEED || ++counter) */
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++block.counter;
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blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
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nbytes -= i;
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@ -1426,10 +1308,7 @@ static void __init init_std_data(void)
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int __init rand_initialize(void)
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{
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init_std_data();
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if (crng_need_final_init)
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crng_finalize_init();
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crng_initialize_primary();
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crng_global_init_time = jiffies;
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crng_initialize();
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if (ratelimit_disable) {
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urandom_warning.interval = 0;
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unseeded_warning.interval = 0;
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@ -1599,8 +1478,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
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return -EPERM;
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if (crng_init < 2)
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return -ENODATA;
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crng_reseed(&primary_crng);
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WRITE_ONCE(crng_global_init_time, jiffies - 1);
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crng_reseed();
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return 0;
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default:
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return -EINVAL;
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