[apple/xnu.git] / osfmk / prng / prng_random.c

/*
 * Copyright (c) 2013 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
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 */

#include <kern/locks.h>
#include <kern/cpu_number.h>
#include <libkern/section_keywords.h>
#include <libkern/crypto/sha2.h>
#include <machine/machine_cpu.h>
#include <machine/machine_routines.h>
#include <pexpert/pexpert.h>
#include <sys/random.h>
#include <prng/random.h>
#include <prng/entropy.h>
#include <corecrypto/ccdigest.h>
#include <corecrypto/ccdrbg.h>
#include <corecrypto/cckprng.h>
#include <corecrypto/ccsha2.h>

static struct cckprng_ctx *prng_ctx;

static SECURITY_READ_ONLY_LATE(struct cckprng_funcs) prng_funcs;
static SECURITY_READ_ONLY_LATE(int) prng_ready;

extern entropy_data_t EntropyData;

#define SEED_SIZE (SHA256_DIGEST_LENGTH)
static uint8_t bootseed[SEED_SIZE];

static void
bootseed_init_bootloader(const struct ccdigest_info * di, ccdigest_ctx_t ctx)
{
        uint8_t seed[64];
        uint32_t n;

        n = PE_get_random_seed(seed, sizeof(seed));
        if (n < sizeof(seed)) {
                /*
                 * Insufficient entropy is fatal.  We must fill the
                 * entire entropy buffer during initializaton.
                 */
                panic("Expected %lu seed bytes from bootloader, but got %u.\n", sizeof(seed), n);
        }

        ccdigest_update(di, ctx, sizeof(seed), seed);
        cc_clear(sizeof(seed), seed);
}

#if defined(__x86_64__)
#include <i386/cpuid.h>

static void
bootseed_init_native(const struct ccdigest_info * di, ccdigest_ctx_t ctx)
{
        uint64_t x;
        uint8_t ok;
        size_t i = 0;
        size_t n;

        if (cpuid_leaf7_features() & CPUID_LEAF7_FEATURE_RDSEED) {
                n = SEED_SIZE / sizeof(x);

                while (i < n) {
                        asm volatile ("rdseed %0; setc %1" : "=r"(x), "=qm"(ok) : : "cc");
                        if (ok) {
                                ccdigest_update(di, ctx, sizeof(x), &x);
                                i += 1;
                        } else {
                                // Intel recommends to pause between unsuccessful rdseed attempts.
                                cpu_pause();
                        }
                }
        } else if (cpuid_features() & CPUID_FEATURE_RDRAND) {
                // The Intel documentation guarantees a reseed every 512 rdrand calls.
                n = (SEED_SIZE / sizeof(x)) * 512;

                while (i < n) {
                        asm volatile ("rdrand %0; setc %1" : "=r"(x), "=qm"(ok) : : "cc");
                        if (ok) {
                                ccdigest_update(di, ctx, sizeof(x), &x);
                                i += 1;
                        } else {
                                // Intel does not recommend pausing between unsuccessful rdrand attempts.
                        }
                }
        }

        cc_clear(sizeof(x), &x);
}

#else

static void
bootseed_init_native(__unused const struct ccdigest_info * di, __unused ccdigest_ctx_t ctx)
{
}

#endif

static void
bootseed_init(void)
{
        const struct ccdigest_info * di = &ccsha256_ltc_di;

        ccdigest_di_decl(di, ctx);
        ccdigest_init(di, ctx);

        bootseed_init_bootloader(di, ctx);
        bootseed_init_native(di, ctx);

        ccdigest_final(di, ctx, bootseed);
        ccdigest_di_clear(di, ctx);
}

#define EARLY_RANDOM_STATE_STATIC_SIZE (264)

static struct {
        uint8_t drbg_state[EARLY_RANDOM_STATE_STATIC_SIZE];
        struct ccdrbg_info drbg_info;
        const struct ccdrbg_nisthmac_custom drbg_custom;
} erandom = {.drbg_custom = {
                     .di         = &ccsha256_ltc_di,
                     .strictFIPS = 0,
             }};

static void read_erandom(void * buf, size_t nbytes);

/*
 * Return a uniformly distributed 64-bit random number.
 *
 * This interface should have minimal dependencies on kernel services,
 * and thus be available very early in the life of the kernel.
 *
 * This provides cryptographically secure randomness contingent on the
 * quality of the seed. It is seeded (lazily) with entropy provided by
 * the Booter.
 *
 * The implementation is a NIST HMAC-SHA256 DRBG instance used as
 * follows:
 *
 *  - When first called (on macOS this is very early while page tables
 *    are being built) early_random() calls ccdrbg_factory_hmac() to
 *    set-up a ccdbrg info structure.
 *
 *  - The boot seed (64 bytes) is hashed with SHA256. Where available,
 *    hardware RNG outputs are mixed into the seed. (See
 *    bootseed_init.) The resulting seed is 32 bytes.
 *
 *  - The ccdrbg state structure is a statically allocated area which
 *    is then initialized by calling the ccdbrg_init method. The
 *    initial entropy is the 32-byte seed described above. The nonce
 *    is an 8-byte timestamp from ml_get_timebase(). The
 *    personalization data provided is a fixed string.
 *
 *  - 64-bit outputs are generated via read_erandom, a wrapper around
 *    the ccdbrg_generate method. (Since "strict FIPS" is disabled,
 *    the DRBG will never request a reseed.)
 *
 *  - After the kernel PRNG is initialized, read_erandom defers
 *    generation to it via read_random_generate. (Note that this
 *    function acquires a per-processor mutex.)
 */
uint64_t
early_random(void)
{
        uint64_t result;
        uint64_t nonce;
        int rc;
        const char ps[] = "xnu early random";
        static int init = 0;

        if (init == 0) {
                bootseed_init();

                /* Init DRBG for NIST HMAC */
                ccdrbg_factory_nisthmac(&erandom.drbg_info, &erandom.drbg_custom);
                assert(erandom.drbg_info.size <= sizeof(erandom.drbg_state));

                /*
                 * Init our DBRG from the boot entropy and a timestamp as nonce
                 * and the cpu number as personalization.
                 */
                assert(sizeof(bootseed) > sizeof(nonce));
                nonce = ml_get_timebase();
                rc = ccdrbg_init(&erandom.drbg_info, (struct ccdrbg_state *)erandom.drbg_state, sizeof(bootseed), bootseed, sizeof(nonce), &nonce, sizeof(ps) - 1, ps);
                if (rc != CCDRBG_STATUS_OK) {
                        panic("ccdrbg_init() returned %d", rc);
                }

                cc_clear(sizeof(nonce), &nonce);

                init = 1;
        }

        read_erandom(&result, sizeof(result));

        return result;
}

static void
read_random_generate(uint8_t *buffer, size_t numbytes);

static void
read_erandom(void * buf, size_t nbytes)
{
        uint8_t * buffer_bytes = buf;
        size_t n;
        int rc;

        // We defer to the kernel PRNG after it has been installed and
        // initialized. This happens during corecrypto kext
        // initialization.
        if (prng_ready) {
                read_random_generate(buf, nbytes);
                return;
        }

        // The DBRG request size is limited, so we break the request into
        // chunks.
        while (nbytes > 0) {
                n = MIN(nbytes, PAGE_SIZE);

                // Since "strict FIPS" is disabled, the DRBG will never
                // request a reseed; therefore, we panic on any error
                rc = ccdrbg_generate(&erandom.drbg_info, (struct ccdrbg_state *)erandom.drbg_state, n, buffer_bytes, 0, NULL);
                if (rc != CCDRBG_STATUS_OK) {
                        panic("read_erandom ccdrbg error %d\n", rc);
                }

                buffer_bytes += n;
                nbytes -= n;
        }
}

void
read_frandom(void * buffer, u_int numBytes)
{
        read_erandom(buffer, numBytes);
}

void
register_and_init_prng(struct cckprng_ctx *ctx, const struct cckprng_funcs *funcs)
{
        assert(cpu_number() == master_cpu);
        assert(!prng_ready);

        entropy_buffer_init();

        prng_ctx = ctx;
        prng_funcs = *funcs;

        uint64_t nonce = ml_get_timebase();
        prng_funcs.init(prng_ctx, MAX_CPUS, EntropyData.buffer_size, EntropyData.buffer, &EntropyData.sample_count, sizeof(bootseed), bootseed, sizeof(nonce), &nonce);
        prng_funcs.initgen(prng_ctx, master_cpu);
        prng_ready = 1;

        cc_clear(sizeof(bootseed), bootseed);
        cc_clear(sizeof(erandom), &erandom);
}

void
random_cpu_init(int cpu)
{
        assert(cpu != master_cpu);

        if (!prng_ready) {
                panic("random_cpu_init: kernel prng has not been installed");
        }

        prng_funcs.initgen(prng_ctx, cpu);
}

/* export good random numbers to the rest of the kernel */
void
read_random(void * buffer, u_int numbytes)
{
        prng_funcs.refresh(prng_ctx);
        read_random_generate(buffer, numbytes);
}

static void
ensure_gsbase(void)
{
#if defined(__x86_64__) && (DEVELOPMENT || DEBUG)
        /*
         * Calling cpu_number() before gsbase is initialized is potentially
         * catastrophic, so assert that it's not set to the magic value set
         * in i386_init.c before proceeding with the call.  We cannot use
         * assert here because it ultimately calls panic, which executes
         * operations that involve accessing %gs-relative data (and additionally
         * causes a debug trap which will not work properly this early in boot.)
         */
        if (rdmsr64(MSR_IA32_GS_BASE) == EARLY_GSBASE_MAGIC) {
                kprintf("[early_random] Cannot proceed: GSBASE is not initialized\n");
                hlt();
                /*NOTREACHED*/
        }
#endif
}

static void
read_random_generate(uint8_t *buffer, size_t numbytes)
{
        ensure_gsbase();

        while (numbytes > 0) {
                size_t n = MIN(numbytes, CCKPRNG_GENERATE_MAX_NBYTES);

                prng_funcs.generate(prng_ctx, cpu_number(), n, buffer);

                buffer += n;
                numbytes -= n;
        }
}

int
write_random(void * buffer, u_int numbytes)
{
        uint8_t seed[SHA256_DIGEST_LENGTH];
        SHA256_CTX ctx;

        /* hash the input to minimize the time we need to hold the lock */
        SHA256_Init(&ctx);
        SHA256_Update(&ctx, buffer, numbytes);
        SHA256_Final(seed, &ctx);

        prng_funcs.reseed(prng_ctx, sizeof(seed), seed);
        cc_clear(sizeof(seed), seed);

        return 0;
}

/*
 * Boolean PRNG for generating booleans to randomize order of elements
 * in certain kernel data structures. The algorithm is a
 * modified version of the KISS RNG proposed in the paper:
 * http://stat.fsu.edu/techreports/M802.pdf
 * The modifications have been documented in the technical paper
 * paper from UCL:
 * http://www0.cs.ucl.ac.uk/staff/d.jones/GoodPracticeRNG.pdf
 */

/* Initialize the PRNG structures. */
void
random_bool_init(struct bool_gen * bg)
{
        /* Seed the random boolean generator */
        read_frandom(bg->seed, sizeof(bg->seed));
        bg->state = 0;
        simple_lock_init(&bg->lock, 0);
}

/* Generate random bits and add them to an entropy pool. */
void
random_bool_gen_entropy(struct bool_gen * bg, unsigned int * buffer, int count)
{
        simple_lock(&bg->lock, LCK_GRP_NULL);
        int i, t;
        for (i = 0; i < count; i++) {
                bg->seed[1] ^= (bg->seed[1] << 5);
                bg->seed[1] ^= (bg->seed[1] >> 7);
                bg->seed[1] ^= (bg->seed[1] << 22);
                t           = bg->seed[2] + bg->seed[3] + bg->state;
                bg->seed[2] = bg->seed[3];
                bg->state   = t < 0;
                bg->seed[3] = t & 2147483647;
                bg->seed[0] += 1411392427;
                buffer[i] = (bg->seed[0] + bg->seed[1] + bg->seed[3]);
        }
        simple_unlock(&bg->lock);
}

/* Get some number of bits from the entropy pool, refilling if necessary. */
unsigned int
random_bool_gen_bits(struct bool_gen * bg, unsigned int * buffer, unsigned int count, unsigned int numbits)
{
        unsigned int index = 0;
        unsigned int rbits = 0;
        for (unsigned int bitct = 0; bitct < numbits; bitct++) {
                /*
                 * Find a portion of the buffer that hasn't been emptied.
                 * We might have emptied our last index in the previous iteration.
                 */
                while (index < count && buffer[index] == 0) {
                        index++;
                }

                /* If we've exhausted the pool, refill it. */
                if (index == count) {
                        random_bool_gen_entropy(bg, buffer, count);
                        index = 0;
                }

                /* Collect-a-bit */
                unsigned int bit = buffer[index] & 1;
                buffer[index]    = buffer[index] >> 1;
                rbits            = bit | (rbits << 1);
        }
        return rbits;
}