Add Windows support for getentropy() and arc4random()

Import from OpenBSD.

COPYING

@@ -449,6 +449,7 @@ Files:
  src/arc4random_openbsd.h
  src/arc4random_uniform.c
  src/arc4random_unix.h
+ src/arc4random_win.h
  src/closefrom.c
  src/getentropy_aix.c
  src/getentropy_bsd.c
@@ -457,6 +458,7 @@ Files:
  src/getentropy_linux.c
  src/getentropy_osx.c
  src/getentropy_solaris.c
+ src/getentropy_win.c
  src/readpassphrase.c
  src/reallocarray.c
  src/strlcat.c

src/Makefile.am

@@ -16,6 +16,7 @@ libbsd_la_included_sources = \
 	getentropy_linux.c \
 	getentropy_osx.c \
 	getentropy_solaris.c \
+	getentropy_win.c \
 	$(nil)
 
 EXTRA_DIST = \
@@ -64,6 +65,7 @@ libbsd_la_SOURCES = \
 	arc4random_openbsd.h \
 	arc4random_uniform.c \
 	arc4random_unix.h \
+	arc4random_win.h \
 	bsd_getopt.c \
 	chacha_private.h \
 	closefrom.c \

src/arc4random.h

@@ -36,6 +36,8 @@ getentropy(void *buf, size_t len);
 #include "arc4random_openbsd.h"
 #elif defined(__linux__)
 #include "arc4random_linux.h"
+#elif defined(_WIN32)
+#include "arc4random_win.h"
 #else
 #include "arc4random_unix.h"
 #endif

src/arc4random_win.h

@@ -0,0 +1,78 @@
+/*	$OpenBSD: arc4random_win.h,v 1.6 2016/06/30 12:17:29 bcook 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 <windows.h>
+
+static volatile HANDLE arc4random_mtx = NULL;
+
+/*
+ * Initialize the mutex on the first lock attempt. On collision, each thread
+ * will attempt to allocate a mutex and compare-and-swap it into place as the
+ * global mutex. On failure to swap in the global mutex, the mutex is closed.
+ */
+#define _ARC4_LOCK() { \
+	if (!arc4random_mtx) { \
+		HANDLE p = CreateMutex(NULL, FALSE, NULL); \
+		if (InterlockedCompareExchangePointer((void **)&arc4random_mtx, (void *)p, NULL)) \
+			CloseHandle(p); \
+	} \
+	WaitForSingleObject(arc4random_mtx, INFINITE); \
+} \
+
+#define _ARC4_UNLOCK() ReleaseMutex(arc4random_mtx)
+
+static inline void
+_getentropy_fail(void)
+{
+	TerminateProcess(GetCurrentProcess(), 0);
+}
+
+static inline int
+_rs_allocate(struct _rs **rsp, struct _rsx **rsxp)
+{
+	*rsp = VirtualAlloc(NULL, sizeof(**rsp),
+	    MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+	if (*rsp == NULL)
+		return (-1);
+
+	*rsxp = VirtualAlloc(NULL, sizeof(**rsxp),
+	    MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+	if (*rsxp == NULL) {
+		VirtualFree(*rsp, 0, MEM_RELEASE);
+		*rsp = NULL;
+		return (-1);
+	}
+	return (0);
+}
+
+static inline void
+_rs_forkhandler(void)
+{
+}
+
+static inline void
+_rs_forkdetect(void)
+{
+}

src/getentropy.c

@@ -40,6 +40,8 @@
 #include "getentropy_aix.c"
 #elif defined(__hpux)
 #include "getentropy_hpux.c"
+#elif defined(_WIN32)
+#include "getentropy_win.c"
 #else
 #error "No getentropy hooks defined for this platform."
 #endif

src/getentropy_win.c

@@ -0,0 +1,59 @@
+/*	$OpenBSD: getentropy_win.c,v 1.5 2016/08/07 03:27:21 tb Exp $	*/
+
+/*
+ * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
+ * Copyright (c) 2014, Bob Beck <beck@obtuse.com>
+ *
+ * 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.
+ *
+ * Emulation of getentropy(2) as documented at:
+ * http://man.openbsd.org/getentropy.2
+ */
+
+#include <windows.h>
+#include <errno.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <wincrypt.h>
+#include <process.h>
+
+int	getentropy(void *buf, size_t len);
+
+/*
+ * On Windows, CryptGenRandom is supposed to be a well-seeded
+ * cryptographically strong random number generator.
+ */
+int
+getentropy(void *buf, size_t len)
+{
+	HCRYPTPROV provider;
+
+	if (len > 256) {
+		errno = EIO;
+		return (-1);
+	}
+
+	if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
+	    CRYPT_VERIFYCONTEXT) == 0)
+		goto fail;
+	if (CryptGenRandom(provider, len, buf) == 0) {
+		CryptReleaseContext(provider, 0);
+		goto fail;
+	}
+	CryptReleaseContext(provider, 0);
+	return (0);
+
+fail:
+	errno = EIO;
+	return (-1);
+}