crypto/rand, internal/syscall/unix: add support for getrandom syscall on solaris

The getrandom syscall is available on Solaris and Illumos, see
https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html and
https://illumos.org/man/2/getrandom

Change-Id: Id1c65d6a5b2fbc80d20b43d8b32dab137ca950ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/299134
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/crypto/rand/rand_batched.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build linux || freebsd || dragonfly
-// +build linux freebsd dragonfly
+//go:build linux || freebsd || dragonfly || solaris
+// +build linux freebsd dragonfly solaris
 
 package rand
 

src/crypto/rand/rand_batched_test.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build linux || freebsd || dragonfly
-// +build linux freebsd dragonfly
+//go:build linux || freebsd || dragonfly || solaris
+// +build linux freebsd dragonfly solaris
 
 package rand
 

src/crypto/rand/rand_solaris.go

@@ -0,0 +1,10 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rand
+
+// maxGetRandomRead is the maximum number of bytes to ask for in one call to the
+// getrandom() syscall. Across all the Solaris platforms, 256 bytes is the
+// lowest number of bytes returned atomically per call.
+const maxGetRandomRead = 1 << 8

src/internal/syscall/unix/getrandom_solaris.go

@@ -0,0 +1,53 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+import (
+	"sync/atomic"
+	"syscall"
+	"unsafe"
+)
+
+//go:cgo_import_dynamic libc_getrandom getrandom "libc.so"
+
+//go:linkname procGetrandom libc_getrandom
+
+var procGetrandom uintptr
+
+var getrandomUnsupported int32 // atomic
+
+// GetRandomFlag is a flag supported by the getrandom system call.
+type GetRandomFlag uintptr
+
+const (
+	// GRND_NONBLOCK means return EAGAIN rather than blocking.
+	GRND_NONBLOCK GetRandomFlag = 0x0001
+
+	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
+	GRND_RANDOM GetRandomFlag = 0x0002
+)
+
+// GetRandom calls the getrandom system call.
+func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	if atomic.LoadInt32(&getrandomUnsupported) != 0 {
+		return 0, syscall.ENOSYS
+	}
+	r1, _, errno := syscall6(uintptr(unsafe.Pointer(&procGetrandom)),
+		3,
+		uintptr(unsafe.Pointer(&p[0])),
+		uintptr(len(p)),
+		uintptr(flags),
+		0, 0, 0)
+	if errno != 0 {
+		if errno == syscall.ENOSYS {
+			atomic.StoreInt32(&getrandomUnsupported, 1)
+		}
+		return 0, errno
+	}
+	return int(r1), nil
+}