crypto/rand: use arc4random_buf() on OpenBSD

OpenBSD system calls are mediated by libc anyway, and arc4random_buf()
is the preferred mechanism to obtain random bytes.

Also, rename NetBSD's function to reflect it's not actually calling
getentropy(3).

Cq-Include-Trybots: luci.golang.try:gotip-openbsd-amd64
Change-Id: Id1f3f7af16750537e2420bcf44b086de5854198c
Reviewed-on: https://go-review.googlesource.com/c/go/+/608395
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Bypass: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>

5 files changed, 26 insertions, 46 deletions

diff --git a/src/internal/syscall/unix/getentropy_netbsd.go b/src/internal/syscall/unix/arandom_netbsd.go
index 02bac1be00..23ca8739e8 100644
--- a/src/internal/syscall/unix/getentropy_netbsd.go
+++ b/src/internal/syscall/unix/arandom_netbsd.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build netbsd
-
 package unix
 
 import (
@@ -17,7 +15,7 @@ const (
 	_KERN_ARND = 81
 )
 
-func GetEntropy(p []byte) error {
+func Arandom(p []byte) error {
 	mib := [2]uint32{_CTL_KERN, _KERN_ARND}
 	n := uintptr(len(p))
 	_, _, errno := syscall.Syscall6(
diff --git a/src/internal/syscall/unix/arc4random_openbsd.go b/src/internal/syscall/unix/arc4random_openbsd.go
new file mode 100644
index 0000000000..652e0cb19d
--- /dev/null
+++ b/src/internal/syscall/unix/arc4random_openbsd.go
@@ -0,0 +1,23 @@
+// Copyright 2024 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 (
+	"internal/abi"
+	"syscall"
+	"unsafe"
+)
+
+//go:linkname syscall_syscall syscall.syscall
+func syscall_syscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno)
+
+//go:cgo_import_dynamic libc_arc4random_buf arc4random_buf "libc.so"
+
+func libc_arc4random_buf_trampoline()
+
+func ARC4Random(p []byte) {
+	syscall_syscall(abi.FuncPCABI0(libc_arc4random_buf_trampoline),
+		uintptr(unsafe.Pointer(unsafe.SliceData(p))), uintptr(len(p)), 0)
+}
diff --git a/src/internal/syscall/unix/asm_openbsd.s b/src/internal/syscall/unix/asm_openbsd.s
index cc54a14ca5..d6c4320539 100644
--- a/src/internal/syscall/unix/asm_openbsd.s
+++ b/src/internal/syscall/unix/asm_openbsd.s
@@ -8,3 +8,5 @@
 
 TEXT ·libc_faccessat_trampoline(SB),NOSPLIT,$0-0
         JMP	libc_faccessat(SB)
+TEXT ·libc_arc4random_buf_trampoline(SB),NOSPLIT,$0-0
+        JMP	libc_arc4random_buf(SB)
diff --git a/src/internal/syscall/unix/getentropy_openbsd.go b/src/internal/syscall/unix/getentropy_openbsd.go
deleted file mode 100644
index 7516ac7ce7..0000000000
--- a/src/internal/syscall/unix/getentropy_openbsd.go
+++ /dev/null
@@ -1,18 +0,0 @@
-// Copyright 2022 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.
-
-//go:build openbsd && !mips64
-
-package unix
-
-import _ "unsafe" // for linkname
-
-// GetEntropy calls the OpenBSD getentropy system call.
-func GetEntropy(p []byte) error {
-	return getentropy(p)
-}
-
-//go:linkname getentropy syscall.getentropy
-//go:noescape
-func getentropy(p []byte) error
diff --git a/src/internal/syscall/unix/getentropy_openbsd_mips64.go b/src/internal/syscall/unix/getentropy_openbsd_mips64.go
deleted file mode 100644
index d5caa8095a..0000000000
--- a/src/internal/syscall/unix/getentropy_openbsd_mips64.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2016 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 (
-	"syscall"
-	"unsafe"
-)
-
-// getentropy(2)'s syscall number, from /usr/src/sys/kern/syscalls.master
-const entropyTrap uintptr = 7
-
-// GetEntropy calls the OpenBSD getentropy system call.
-func GetEntropy(p []byte) error {
-	_, _, errno := syscall.Syscall(entropyTrap,
-		uintptr(unsafe.Pointer(&p[0])),
-		uintptr(len(p)),
-		0)
-	if errno != 0 {
-		return errno
-	}
-	return nil
-}