diff options
Diffstat (limited to 'sys/kern/sys_getrandom.c')
| -rw-r--r-- | sys/kern/sys_getrandom.c | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/sys/kern/sys_getrandom.c b/sys/kern/sys_getrandom.c new file mode 100644 index 00000000000..947b5d79717 --- /dev/null +++ b/sys/kern/sys_getrandom.c @@ -0,0 +1,246 @@ +/* $NetBSD: sys_getrandom.c,v 1.1 2020/08/14 00:53:16 riastradh Exp $ */ + +/*- + * Copyright (c) 2020 The NetBSD Foundation, Inc. + * All rights reserved. + * + * This code is derived from software contributed to The NetBSD Foundation + * by Taylor R. Campbell. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS + * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED + * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS + * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +/* + * getrandom() system call + */ + +#include <sys/cdefs.h> +__KERNEL_RCSID(0, "$NetBSD: sys_getrandom.c,v 1.1 2020/08/14 00:53:16 riastradh Exp $"); + +#include <sys/types.h> +#include <sys/param.h> + +#include <sys/atomic.h> +#include <sys/cprng.h> +#include <sys/entropy.h> +#include <sys/kmem.h> +#include <sys/lwp.h> +#include <sys/proc.h> +#include <sys/random.h> +#include <sys/sched.h> +#include <sys/signalvar.h> +#include <sys/syscallargs.h> +#include <sys/uio.h> + +#include <crypto/nist_hash_drbg/nist_hash_drbg.h> + +#define RANDOM_BUFSIZE 512 + +int +dogetrandom(struct uio *uio, unsigned int flags) +{ + uint8_t seed[NIST_HASH_DRBG_SEEDLEN_BYTES] = {0}; + struct nist_hash_drbg drbg; + uint8_t *buf; + int extractflags = 0; + int error; + + KASSERT((flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) == 0); + KASSERT((flags & (GRND_RANDOM|GRND_INSECURE)) != + (GRND_RANDOM|GRND_INSECURE)); + + /* Get a buffer for transfers. */ + buf = kmem_alloc(RANDOM_BUFSIZE, KM_SLEEP); + + /* + * Fast path: for short reads other than from /dev/random, if + * seeded or if INSECURE, just draw from per-CPU cprng_strong. + */ + if (uio->uio_resid <= RANDOM_BUFSIZE && + !ISSET(flags, GRND_RANDOM) && + (entropy_ready() || ISSET(flags, GRND_INSECURE))) { + /* Generate data and transfer it out. */ + cprng_strong(user_cprng, buf, uio->uio_resid, 0); + error = uiomove(buf, uio->uio_resid, uio); + goto out; + } + + /* + * Try to get a seed from the entropy pool. Fail if we would + * block. If GRND_INSECURE, always return something even if it + * is partial entropy; if !GRND_INSECURE, set ENTROPY_HARDFAIL + * in order to tell entropy_extract not to bother drawing + * anything from a partial pool if we can't get full entropy. + */ + if (!ISSET(flags, GRND_NONBLOCK) && !ISSET(flags, GRND_INSECURE)) + extractflags |= ENTROPY_WAIT|ENTROPY_SIG; + if (!ISSET(flags, GRND_INSECURE)) + extractflags |= ENTROPY_HARDFAIL; + error = entropy_extract(seed, sizeof seed, extractflags); + if (error && !ISSET(flags, GRND_INSECURE)) + goto out; + + /* Instantiate the DRBG. */ + if (nist_hash_drbg_instantiate(&drbg, seed, sizeof seed, NULL, 0, + NULL, 0)) + panic("nist_hash_drbg_instantiate"); + + /* Promptly zero the seed. */ + explicit_memset(seed, 0, sizeof seed); + + /* Generate data. */ + error = 0; + while (uio->uio_resid) { + size_t n = MIN(uio->uio_resid, RANDOM_BUFSIZE); + + /* + * Clamp /dev/random output to the entropy capacity and + * seed size. Programs can't rely on long reads. + */ + if (ISSET(flags, GRND_RANDOM)) { + n = MIN(n, ENTROPY_CAPACITY); + n = MIN(n, sizeof seed); + /* + * Guarantee never to return more than one + * buffer in this case to minimize bookkeeping. + */ + CTASSERT(ENTROPY_CAPACITY <= RANDOM_BUFSIZE); + CTASSERT(sizeof seed <= RANDOM_BUFSIZE); + } + + /* + * Try to generate a block of data, but if we've hit + * the DRBG reseed interval, reseed. + */ + if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0)) { + /* + * Get a fresh seed without blocking -- we have + * already generated some output so it is not + * useful to block. This can fail only if the + * request is obscenely large, so it is OK for + * either /dev/random or /dev/urandom to fail: + * we make no promises about gigabyte-sized + * reads happening all at once. + */ + error = entropy_extract(seed, sizeof seed, + ENTROPY_HARDFAIL); + if (error) + break; + + /* Reseed and try again. */ + if (nist_hash_drbg_reseed(&drbg, seed, sizeof seed, + NULL, 0)) + panic("nist_hash_drbg_reseed"); + + /* Promptly zero the seed. */ + explicit_memset(seed, 0, sizeof seed); + + /* If it fails now, that's a bug. */ + if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0)) + panic("nist_hash_drbg_generate"); + } + + /* Transfer n bytes out. */ + error = uiomove(buf, n, uio); + if (error) + break; + + /* + * If this is /dev/random, stop here, return what we + * have, and force the next read to reseed. Programs + * can't rely on /dev/random for long reads. + */ + if (ISSET(flags, GRND_RANDOM)) { + error = 0; + break; + } + + /* Yield if requested. */ + if (curcpu()->ci_schedstate.spc_flags & SPCF_SHOULDYIELD) + preempt(); + + /* Check for interruption after at least 256 bytes. */ + CTASSERT(RANDOM_BUFSIZE >= 256); + if (__predict_false(curlwp->l_flag & LW_PENDSIG) && + sigispending(curlwp, 0)) { + error = EINTR; + break; + } + } + +out: /* Zero the buffer and free it. */ + explicit_memset(buf, 0, RANDOM_BUFSIZE); + kmem_free(buf, RANDOM_BUFSIZE); + + return error; +} + +int +sys_getrandom(struct lwp *l, const struct sys_getrandom_args *uap, + register_t *retval) +{ + /* { + syscallarg(void *) buf; + syscallarg(size_t) buflen; + syscallarg(unsigned) flags; + } */ + void *buf = SCARG(uap, buf); + size_t buflen = SCARG(uap, buflen); + int flags = SCARG(uap, flags); + int error; + + /* Set up an iov and uio to read into the user's buffer. */ + struct iovec iov = { .iov_base = buf, .iov_len = buflen }; + struct uio uio = { + .uio_iov = &iov, + .uio_iovcnt = 1, + .uio_offset = 0, + .uio_resid = buflen, + .uio_rw = UIO_READ, + .uio_vmspace = curproc->p_vmspace, + }; + + /* Validate the flags. */ + if (flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) { + /* Unknown flags. */ + error = EINVAL; + goto out; + } + if ((flags & (GRND_RANDOM|GRND_INSECURE)) == + (GRND_RANDOM|GRND_INSECURE)) { + /* Nonsensical combination. */ + error = EINVAL; + goto out; + } + + /* Do it. */ + error = dogetrandom(&uio, flags); + +out: /* + * If we transferred anything, return the number of bytes + * transferred and suppress error; otherwise return the error. + */ + *retval = buflen - uio.uio_resid; + if (*retval) + error = 0; + return error; +} |
