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/* $OpenBSD: arc4random.h,v 1.4 2015/01/15 06:57:18 deraadt Exp $ */
/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
* Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
* Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* Stub functions for portability.
*/
#include <sys/elf.h>
#include <sys/endian.h>
#include <sys/mman.h>
#if ARC4RANDOM_FXRNG != 0
#include <sys/time.h> /* for sys/vdso.h only. */
#include <sys/vdso.h>
#include <machine/atomic.h>
#endif
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#if ARC4RANDOM_FXRNG != 0
/*
* The kernel root seed version is a 64-bit counter, but we truncate it to a
* 32-bit value in userspace for the convenience of 32-bit platforms. 32-bit
* rollover is not possible with the current reseed interval (1 hour at limit)
* without dynamic addition of new random devices (which also force a reseed in
* the FXRNG design). We don't have any dynamic device mechanism at this
* time, and anyway something else is very wrong if billions of new devices are
* being added.
*
* As is, it takes roughly 456,000 years of runtime to overflow the 32-bit
* version.
*/
#define fxrng_load_acq_generation(x) atomic_load_acq_32(x)
static struct vdso_fxrng_generation_1 *vdso_fxrngp;
#endif
static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
#define _ARC4_LOCK() \
do { \
if (__isthreaded) \
_pthread_mutex_lock(&arc4random_mtx); \
} while (0)
#define _ARC4_UNLOCK() \
do { \
if (__isthreaded) \
_pthread_mutex_unlock(&arc4random_mtx); \
} while (0)
static inline void
_getentropy_fail(void)
{
raise(SIGKILL);
}
static inline void
_rs_initialize_fxrng(void)
{
#if ARC4RANDOM_FXRNG != 0
struct vdso_fxrng_generation_1 *fxrngp;
int error;
error = _elf_aux_info(AT_FXRNG, &fxrngp, sizeof(fxrngp));
if (error != 0) {
/*
* New userspace on an old or !RANDOM_FENESTRASX kernel; or an
* arch that does not have a VDSO page.
*/
return;
}
/* Old userspace on newer kernel. */
if (fxrngp->fx_vdso_version != VDSO_FXRNG_VER_1)
return;
vdso_fxrngp = fxrngp;
#endif
}
static inline int
_rs_allocate(struct _rs **rsp, struct _rsx **rsxp)
{
struct {
struct _rs rs;
struct _rsx rsx;
} *p;
if ((p = mmap(NULL, sizeof(*p), PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
return (-1);
/* Allow bootstrapping arc4random.c on Linux/macOS */
#ifdef INHERIT_ZERO
if (minherit(p, sizeof(*p), INHERIT_ZERO) == -1) {
munmap(p, sizeof(*p));
return (-1);
}
#endif
_rs_initialize_fxrng();
*rsp = &p->rs;
*rsxp = &p->rsx;
return (0);
}
/*
* This isn't only detecting fork. We're also using the existing callback from
* _rs_stir_if_needed() to force arc4random(3) to reseed if the fenestrasX root
* seed version has changed. (That is, the root random(4) has reseeded from
* pooled entropy.)
*/
static inline void
_rs_forkdetect(void)
{
/* Detect fork (minherit(2) INHERIT_ZERO). */
if (__predict_false(rs == NULL || rsx == NULL))
return;
#if ARC4RANDOM_FXRNG != 0
/* If present, detect kernel FenestrasX seed version change. */
if (vdso_fxrngp == NULL)
return;
if (__predict_true(rsx->rs_seed_generation ==
fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32)))
return;
#endif
/* Invalidate rs_buf to force "stir" (reseed). */
memset(rs, 0, sizeof(*rs));
}
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