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-rw-r--r--sys/kern/sys_getrandom.c246
1 files changed, 246 insertions, 0 deletions
diff --git a/sys/kern/sys_getrandom.c b/sys/kern/sys_getrandom.c
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--- /dev/null
+++ b/sys/kern/sys_getrandom.c
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+/* $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;
+}