1*78c5b0a7Sriastradh /* $NetBSD: sys_getrandom.c,v 1.2 2021/12/28 13:22:43 riastradh Exp $ */
2e2fa4d60Sriastradh
3e2fa4d60Sriastradh /*-
4e2fa4d60Sriastradh * Copyright (c) 2020 The NetBSD Foundation, Inc.
5e2fa4d60Sriastradh * All rights reserved.
6e2fa4d60Sriastradh *
7e2fa4d60Sriastradh * This code is derived from software contributed to The NetBSD Foundation
8e2fa4d60Sriastradh * by Taylor R. Campbell.
9e2fa4d60Sriastradh *
10e2fa4d60Sriastradh * Redistribution and use in source and binary forms, with or without
11e2fa4d60Sriastradh * modification, are permitted provided that the following conditions
12e2fa4d60Sriastradh * are met:
13e2fa4d60Sriastradh * 1. Redistributions of source code must retain the above copyright
14e2fa4d60Sriastradh * notice, this list of conditions and the following disclaimer.
15e2fa4d60Sriastradh * 2. Redistributions in binary form must reproduce the above copyright
16e2fa4d60Sriastradh * notice, this list of conditions and the following disclaimer in the
17e2fa4d60Sriastradh * documentation and/or other materials provided with the distribution.
18e2fa4d60Sriastradh *
19e2fa4d60Sriastradh * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20e2fa4d60Sriastradh * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21e2fa4d60Sriastradh * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22e2fa4d60Sriastradh * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23e2fa4d60Sriastradh * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24e2fa4d60Sriastradh * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25e2fa4d60Sriastradh * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26e2fa4d60Sriastradh * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27e2fa4d60Sriastradh * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28e2fa4d60Sriastradh * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29e2fa4d60Sriastradh * POSSIBILITY OF SUCH DAMAGE.
30e2fa4d60Sriastradh */
31e2fa4d60Sriastradh
32e2fa4d60Sriastradh /*
33e2fa4d60Sriastradh * getrandom() system call
34e2fa4d60Sriastradh */
35e2fa4d60Sriastradh
36e2fa4d60Sriastradh #include <sys/cdefs.h>
37*78c5b0a7Sriastradh __KERNEL_RCSID(0, "$NetBSD: sys_getrandom.c,v 1.2 2021/12/28 13:22:43 riastradh Exp $");
38e2fa4d60Sriastradh
39e2fa4d60Sriastradh #include <sys/types.h>
40e2fa4d60Sriastradh #include <sys/param.h>
41e2fa4d60Sriastradh
42e2fa4d60Sriastradh #include <sys/atomic.h>
43e2fa4d60Sriastradh #include <sys/cprng.h>
44e2fa4d60Sriastradh #include <sys/entropy.h>
45e2fa4d60Sriastradh #include <sys/kmem.h>
46e2fa4d60Sriastradh #include <sys/lwp.h>
47e2fa4d60Sriastradh #include <sys/proc.h>
48e2fa4d60Sriastradh #include <sys/random.h>
49e2fa4d60Sriastradh #include <sys/sched.h>
50e2fa4d60Sriastradh #include <sys/signalvar.h>
51e2fa4d60Sriastradh #include <sys/syscallargs.h>
52e2fa4d60Sriastradh #include <sys/uio.h>
53e2fa4d60Sriastradh
54e2fa4d60Sriastradh #include <crypto/nist_hash_drbg/nist_hash_drbg.h>
55e2fa4d60Sriastradh
56e2fa4d60Sriastradh #define RANDOM_BUFSIZE 512
57e2fa4d60Sriastradh
58e2fa4d60Sriastradh int
dogetrandom(struct uio * uio,unsigned int flags)59e2fa4d60Sriastradh dogetrandom(struct uio *uio, unsigned int flags)
60e2fa4d60Sriastradh {
61e2fa4d60Sriastradh uint8_t seed[NIST_HASH_DRBG_SEEDLEN_BYTES] = {0};
62e2fa4d60Sriastradh struct nist_hash_drbg drbg;
63e2fa4d60Sriastradh uint8_t *buf;
64e2fa4d60Sriastradh int extractflags = 0;
65e2fa4d60Sriastradh int error;
66e2fa4d60Sriastradh
67e2fa4d60Sriastradh KASSERT((flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) == 0);
68e2fa4d60Sriastradh KASSERT((flags & (GRND_RANDOM|GRND_INSECURE)) !=
69e2fa4d60Sriastradh (GRND_RANDOM|GRND_INSECURE));
70e2fa4d60Sriastradh
71e2fa4d60Sriastradh /* Get a buffer for transfers. */
72e2fa4d60Sriastradh buf = kmem_alloc(RANDOM_BUFSIZE, KM_SLEEP);
73e2fa4d60Sriastradh
74e2fa4d60Sriastradh /*
75e2fa4d60Sriastradh * Fast path: for short reads other than from /dev/random, if
76e2fa4d60Sriastradh * seeded or if INSECURE, just draw from per-CPU cprng_strong.
77e2fa4d60Sriastradh */
78e2fa4d60Sriastradh if (uio->uio_resid <= RANDOM_BUFSIZE &&
79e2fa4d60Sriastradh !ISSET(flags, GRND_RANDOM) &&
80e2fa4d60Sriastradh (entropy_ready() || ISSET(flags, GRND_INSECURE))) {
81e2fa4d60Sriastradh /* Generate data and transfer it out. */
82e2fa4d60Sriastradh cprng_strong(user_cprng, buf, uio->uio_resid, 0);
83e2fa4d60Sriastradh error = uiomove(buf, uio->uio_resid, uio);
84e2fa4d60Sriastradh goto out;
85e2fa4d60Sriastradh }
86e2fa4d60Sriastradh
87e2fa4d60Sriastradh /*
88e2fa4d60Sriastradh * Try to get a seed from the entropy pool. Fail if we would
89e2fa4d60Sriastradh * block. If GRND_INSECURE, always return something even if it
90e2fa4d60Sriastradh * is partial entropy; if !GRND_INSECURE, set ENTROPY_HARDFAIL
91e2fa4d60Sriastradh * in order to tell entropy_extract not to bother drawing
92e2fa4d60Sriastradh * anything from a partial pool if we can't get full entropy.
93e2fa4d60Sriastradh */
94e2fa4d60Sriastradh if (!ISSET(flags, GRND_NONBLOCK) && !ISSET(flags, GRND_INSECURE))
95e2fa4d60Sriastradh extractflags |= ENTROPY_WAIT|ENTROPY_SIG;
96e2fa4d60Sriastradh if (!ISSET(flags, GRND_INSECURE))
97e2fa4d60Sriastradh extractflags |= ENTROPY_HARDFAIL;
98e2fa4d60Sriastradh error = entropy_extract(seed, sizeof seed, extractflags);
99e2fa4d60Sriastradh if (error && !ISSET(flags, GRND_INSECURE))
100e2fa4d60Sriastradh goto out;
101e2fa4d60Sriastradh
102e2fa4d60Sriastradh /* Instantiate the DRBG. */
103e2fa4d60Sriastradh if (nist_hash_drbg_instantiate(&drbg, seed, sizeof seed, NULL, 0,
104e2fa4d60Sriastradh NULL, 0))
105e2fa4d60Sriastradh panic("nist_hash_drbg_instantiate");
106e2fa4d60Sriastradh
107e2fa4d60Sriastradh /* Promptly zero the seed. */
108e2fa4d60Sriastradh explicit_memset(seed, 0, sizeof seed);
109e2fa4d60Sriastradh
110e2fa4d60Sriastradh /* Generate data. */
111e2fa4d60Sriastradh error = 0;
112e2fa4d60Sriastradh while (uio->uio_resid) {
113e2fa4d60Sriastradh size_t n = MIN(uio->uio_resid, RANDOM_BUFSIZE);
114e2fa4d60Sriastradh
115e2fa4d60Sriastradh /*
116e2fa4d60Sriastradh * Clamp /dev/random output to the entropy capacity and
117e2fa4d60Sriastradh * seed size. Programs can't rely on long reads.
118e2fa4d60Sriastradh */
119e2fa4d60Sriastradh if (ISSET(flags, GRND_RANDOM)) {
120e2fa4d60Sriastradh n = MIN(n, ENTROPY_CAPACITY);
121e2fa4d60Sriastradh n = MIN(n, sizeof seed);
122e2fa4d60Sriastradh /*
123e2fa4d60Sriastradh * Guarantee never to return more than one
124e2fa4d60Sriastradh * buffer in this case to minimize bookkeeping.
125e2fa4d60Sriastradh */
126e2fa4d60Sriastradh CTASSERT(ENTROPY_CAPACITY <= RANDOM_BUFSIZE);
127e2fa4d60Sriastradh CTASSERT(sizeof seed <= RANDOM_BUFSIZE);
128e2fa4d60Sriastradh }
129e2fa4d60Sriastradh
130e2fa4d60Sriastradh /*
131e2fa4d60Sriastradh * Try to generate a block of data, but if we've hit
132e2fa4d60Sriastradh * the DRBG reseed interval, reseed.
133e2fa4d60Sriastradh */
134e2fa4d60Sriastradh if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0)) {
135e2fa4d60Sriastradh /*
136e2fa4d60Sriastradh * Get a fresh seed without blocking -- we have
137e2fa4d60Sriastradh * already generated some output so it is not
138e2fa4d60Sriastradh * useful to block. This can fail only if the
139e2fa4d60Sriastradh * request is obscenely large, so it is OK for
140e2fa4d60Sriastradh * either /dev/random or /dev/urandom to fail:
141e2fa4d60Sriastradh * we make no promises about gigabyte-sized
142e2fa4d60Sriastradh * reads happening all at once.
143e2fa4d60Sriastradh */
144e2fa4d60Sriastradh error = entropy_extract(seed, sizeof seed,
145e2fa4d60Sriastradh ENTROPY_HARDFAIL);
146e2fa4d60Sriastradh if (error)
147e2fa4d60Sriastradh break;
148e2fa4d60Sriastradh
149e2fa4d60Sriastradh /* Reseed and try again. */
150e2fa4d60Sriastradh if (nist_hash_drbg_reseed(&drbg, seed, sizeof seed,
151e2fa4d60Sriastradh NULL, 0))
152e2fa4d60Sriastradh panic("nist_hash_drbg_reseed");
153e2fa4d60Sriastradh
154e2fa4d60Sriastradh /* Promptly zero the seed. */
155e2fa4d60Sriastradh explicit_memset(seed, 0, sizeof seed);
156e2fa4d60Sriastradh
157e2fa4d60Sriastradh /* If it fails now, that's a bug. */
158e2fa4d60Sriastradh if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0))
159e2fa4d60Sriastradh panic("nist_hash_drbg_generate");
160e2fa4d60Sriastradh }
161e2fa4d60Sriastradh
162e2fa4d60Sriastradh /* Transfer n bytes out. */
163e2fa4d60Sriastradh error = uiomove(buf, n, uio);
164e2fa4d60Sriastradh if (error)
165e2fa4d60Sriastradh break;
166e2fa4d60Sriastradh
167e2fa4d60Sriastradh /*
168e2fa4d60Sriastradh * If this is /dev/random, stop here, return what we
169e2fa4d60Sriastradh * have, and force the next read to reseed. Programs
170e2fa4d60Sriastradh * can't rely on /dev/random for long reads.
171e2fa4d60Sriastradh */
172e2fa4d60Sriastradh if (ISSET(flags, GRND_RANDOM)) {
173e2fa4d60Sriastradh error = 0;
174e2fa4d60Sriastradh break;
175e2fa4d60Sriastradh }
176e2fa4d60Sriastradh
177*78c5b0a7Sriastradh /* Now's a good time to yield if needed. */
178*78c5b0a7Sriastradh preempt_point();
179e2fa4d60Sriastradh
180e2fa4d60Sriastradh /* Check for interruption after at least 256 bytes. */
181e2fa4d60Sriastradh CTASSERT(RANDOM_BUFSIZE >= 256);
182e2fa4d60Sriastradh if (__predict_false(curlwp->l_flag & LW_PENDSIG) &&
183e2fa4d60Sriastradh sigispending(curlwp, 0)) {
184e2fa4d60Sriastradh error = EINTR;
185e2fa4d60Sriastradh break;
186e2fa4d60Sriastradh }
187e2fa4d60Sriastradh }
188e2fa4d60Sriastradh
189e2fa4d60Sriastradh out: /* Zero the buffer and free it. */
190e2fa4d60Sriastradh explicit_memset(buf, 0, RANDOM_BUFSIZE);
191e2fa4d60Sriastradh kmem_free(buf, RANDOM_BUFSIZE);
192e2fa4d60Sriastradh
193e2fa4d60Sriastradh return error;
194e2fa4d60Sriastradh }
195e2fa4d60Sriastradh
196e2fa4d60Sriastradh int
sys_getrandom(struct lwp * l,const struct sys_getrandom_args * uap,register_t * retval)197e2fa4d60Sriastradh sys_getrandom(struct lwp *l, const struct sys_getrandom_args *uap,
198e2fa4d60Sriastradh register_t *retval)
199e2fa4d60Sriastradh {
200e2fa4d60Sriastradh /* {
201e2fa4d60Sriastradh syscallarg(void *) buf;
202e2fa4d60Sriastradh syscallarg(size_t) buflen;
203e2fa4d60Sriastradh syscallarg(unsigned) flags;
204e2fa4d60Sriastradh } */
205e2fa4d60Sriastradh void *buf = SCARG(uap, buf);
206e2fa4d60Sriastradh size_t buflen = SCARG(uap, buflen);
207e2fa4d60Sriastradh int flags = SCARG(uap, flags);
208e2fa4d60Sriastradh int error;
209e2fa4d60Sriastradh
210e2fa4d60Sriastradh /* Set up an iov and uio to read into the user's buffer. */
211e2fa4d60Sriastradh struct iovec iov = { .iov_base = buf, .iov_len = buflen };
212e2fa4d60Sriastradh struct uio uio = {
213e2fa4d60Sriastradh .uio_iov = &iov,
214e2fa4d60Sriastradh .uio_iovcnt = 1,
215e2fa4d60Sriastradh .uio_offset = 0,
216e2fa4d60Sriastradh .uio_resid = buflen,
217e2fa4d60Sriastradh .uio_rw = UIO_READ,
218e2fa4d60Sriastradh .uio_vmspace = curproc->p_vmspace,
219e2fa4d60Sriastradh };
220e2fa4d60Sriastradh
221e2fa4d60Sriastradh /* Validate the flags. */
222e2fa4d60Sriastradh if (flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) {
223e2fa4d60Sriastradh /* Unknown flags. */
224e2fa4d60Sriastradh error = EINVAL;
225e2fa4d60Sriastradh goto out;
226e2fa4d60Sriastradh }
227e2fa4d60Sriastradh if ((flags & (GRND_RANDOM|GRND_INSECURE)) ==
228e2fa4d60Sriastradh (GRND_RANDOM|GRND_INSECURE)) {
229e2fa4d60Sriastradh /* Nonsensical combination. */
230e2fa4d60Sriastradh error = EINVAL;
231e2fa4d60Sriastradh goto out;
232e2fa4d60Sriastradh }
233e2fa4d60Sriastradh
234e2fa4d60Sriastradh /* Do it. */
235e2fa4d60Sriastradh error = dogetrandom(&uio, flags);
236e2fa4d60Sriastradh
237e2fa4d60Sriastradh out: /*
238e2fa4d60Sriastradh * If we transferred anything, return the number of bytes
239e2fa4d60Sriastradh * transferred and suppress error; otherwise return the error.
240e2fa4d60Sriastradh */
241e2fa4d60Sriastradh *retval = buflen - uio.uio_resid;
242e2fa4d60Sriastradh if (*retval)
243e2fa4d60Sriastradh error = 0;
244e2fa4d60Sriastradh return error;
245e2fa4d60Sriastradh }
246