diff options
Diffstat (limited to 'module')
| -rw-r--r-- | module/spl/spl-generic.c | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/module/spl/spl-generic.c b/module/spl/spl-generic.c index dc3e74aa5..88a0fcc51 100644 --- a/module/spl/spl-generic.c +++ b/module/spl/spl-generic.c @@ -41,6 +41,8 @@ #include <sys/kstat.h> #include <sys/file.h> #include <linux/ctype.h> +#include <sys/disp.h> +#include <sys/random.h> #include <linux/kmod.h> #include <linux/math64_compat.h> #include <linux/proc_compat.h> @@ -56,6 +58,112 @@ MODULE_PARM_DESC(spl_hostid, "The system hostid."); proc_t p0 = { 0 }; EXPORT_SYMBOL(p0); +/* + * Xorshift Pseudo Random Number Generator based on work by Sebastiano Vigna + * + * "Further scramblings of Marsaglia's xorshift generators" + * http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf + * + * random_get_pseudo_bytes() is an API function on Illumos whose sole purpose + * is to provide bytes containing random numbers. It is mapped to /dev/urandom + * on Illumos, which uses a "FIPS 186-2 algorithm". No user of the SPL's + * random_get_pseudo_bytes() needs bytes that are of cryptographic quality, so + * we can implement it using a fast PRNG that we seed using Linux' actual + * equivalent to random_get_pseudo_bytes(). We do this by providing each CPU + * with an independent seed so that all calls to random_get_pseudo_bytes() are + * free of atomic instructions. + * + * A consequence of using a fast PRNG is that using random_get_pseudo_bytes() + * to generate words larger than 128 bits will paradoxically be limited to + * `2^128 - 1` possibilities. This is because we have a sequence of `2^128 - 1` + * 128-bit words and selecting the first will implicitly select the second. If + * a caller finds this behavior undesireable, random_get_bytes() should be used + * instead. + * + * XXX: Linux interrupt handlers that trigger within the critical section + * formed by `s[1] = xp[1];` and `xp[0] = s[0];` and call this function will + * see the same numbers. Nothing in the code currently calls this in an + * interrupt handler, so this is considered to be okay. If that becomes a + * problem, we could create a set of per-cpu variables for interrupt handlers + * and use them when in_interrupt() from linux/preempt_mask.h evaluates to + * true. + */ +static DEFINE_PER_CPU(uint64_t[2], spl_pseudo_entropy); + +/* + * spl_rand_next()/spl_rand_jump() are copied from the following CC-0 licensed + * file: + * + * http://xorshift.di.unimi.it/xorshift128plus.c + */ + +static inline uint64_t +spl_rand_next(uint64_t *s) { + uint64_t s1 = s[0]; + const uint64_t s0 = s[1]; + s[0] = s0; + s1 ^= s1 << 23; // a + s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5); // b, c + return (s[1] + s0); +} + +static inline void +spl_rand_jump(uint64_t *s) { + static const uint64_t JUMP[] = { 0x8a5cd789635d2dff, 0x121fd2155c472f96 }; + + uint64_t s0 = 0; + uint64_t s1 = 0; + int i, b; + for(i = 0; i < sizeof JUMP / sizeof *JUMP; i++) + for(b = 0; b < 64; b++) { + if (JUMP[i] & 1ULL << b) { + s0 ^= s[0]; + s1 ^= s[1]; + } + (void) spl_rand_next(s); + } + + s[0] = s0; + s[1] = s1; +} + +int +random_get_pseudo_bytes(uint8_t *ptr, size_t len) +{ + uint64_t *xp, s[2]; + + ASSERT(ptr); + + xp = get_cpu_var(spl_pseudo_entropy); + + s[0] = xp[0]; + s[1] = xp[1]; + + while (len) { + union { + uint64_t ui64; + uint8_t byte[sizeof (uint64_t)]; + }entropy; + int i = MIN(len, sizeof (uint64_t)); + + len -= i; + entropy.ui64 = spl_rand_next(s); + + while (i--) + *ptr++ = entropy.byte[i]; + } + + xp[0] = s[0]; + xp[1] = s[1]; + + put_cpu_var(spl_pseudo_entropy); + + return (0); +} + + +EXPORT_SYMBOL(random_get_pseudo_bytes); + #if BITS_PER_LONG == 32 /* * Support 64/64 => 64 division on a 32-bit platform. While the kernel @@ -502,6 +610,44 @@ spl_kvmem_init(void) return (rc); } +/* + * We initialize the random number generator with 128 bits of entropy from the + * system random number generator. In the improbable case that we have a zero + * seed, we fallback to the system jiffies, unless it is also zero, in which + * situation we use a preprogrammed seed. We step forward by 2^64 iterations to + * initialize each of the per-cpu seeds so that the sequences generated on each + * CPU are guaranteed to never overlap in practice. + */ +static void __init +spl_random_init(void) +{ + uint64_t s[2]; + int i; + + get_random_bytes(s, sizeof (s)); + + if (s[0] == 0 && s[1] == 0) { + if (jiffies != 0) { + s[0] = jiffies; + s[1] = ~0 - jiffies; + } else { + (void) memcpy(s, "improbable seed", sizeof (s)); + } + printk("SPL: get_random_bytes() returned 0 " + "when generating random seed. Setting initial seed to " + "0x%016llx%016llx.", cpu_to_be64(s[0]), cpu_to_be64(s[1])); + } + + for (i = 0; i < NR_CPUS; i++) { + uint64_t *wordp = per_cpu(spl_pseudo_entropy, i); + + spl_rand_jump(s); + + wordp[0] = s[0]; + wordp[1] = s[1]; + } +} + static void spl_kvmem_fini(void) { @@ -514,6 +660,8 @@ spl_init(void) { int rc = 0; + spl_random_init(); + if ((rc = spl_kvmem_init())) goto out1; |