unix: remove arch specific build for openbsd_pledge.go

The pledge code is platform specific, but in no way architecture specific.
As such, drop the +build rule that ties it to specific architectures.

While here also rename openbsd_pledge.go and openbsd_unveil.go so we can
drop the openbsd specific build tags.

Change-Id: I7d83796c8f9b46afe2a6790620205df5f7f3d738
Reviewed-on: https://go-review.googlesource.com/c/sys/+/173677
Reviewed-by: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/pledge_openbsd.go

@@ -0,0 +1,163 @@
+// 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 (
+	"errors"
+	"fmt"
+	"strconv"
+	"syscall"
+	"unsafe"
+)
+
+// Pledge implements the pledge syscall.
+//
+// The pledge syscall does not accept execpromises on OpenBSD releases
+// before 6.3.
+//
+// execpromises must be empty when Pledge is called on OpenBSD
+// releases predating 6.3, otherwise an error will be returned.
+//
+// For more information see pledge(2).
+func Pledge(promises, execpromises string) error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
+	}
+
+	err = pledgeAvailable(maj, min, execpromises)
+	if err != nil {
+		return err
+	}
+
+	pptr, err := syscall.BytePtrFromString(promises)
+	if err != nil {
+		return err
+	}
+
+	// This variable will hold either a nil unsafe.Pointer or
+	// an unsafe.Pointer to a string (execpromises).
+	var expr unsafe.Pointer
+
+	// If we're running on OpenBSD > 6.2, pass execpromises to the syscall.
+	if maj > 6 || (maj == 6 && min > 2) {
+		exptr, err := syscall.BytePtrFromString(execpromises)
+		if err != nil {
+			return err
+		}
+		expr = unsafe.Pointer(exptr)
+	}
+
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)), uintptr(expr), 0)
+	if e != 0 {
+		return e
+	}
+
+	return nil
+}
+
+// PledgePromises implements the pledge syscall.
+//
+// This changes the promises and leaves the execpromises untouched.
+//
+// For more information see pledge(2).
+func PledgePromises(promises string) error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
+	}
+
+	err = pledgeAvailable(maj, min, "")
+	if err != nil {
+		return err
+	}
+
+	// This variable holds the execpromises and is always nil.
+	var expr unsafe.Pointer
+
+	pptr, err := syscall.BytePtrFromString(promises)
+	if err != nil {
+		return err
+	}
+
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)), uintptr(expr), 0)
+	if e != 0 {
+		return e
+	}
+
+	return nil
+}
+
+// PledgeExecpromises implements the pledge syscall.
+//
+// This changes the execpromises and leaves the promises untouched.
+//
+// For more information see pledge(2).
+func PledgeExecpromises(execpromises string) error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
+	}
+
+	err = pledgeAvailable(maj, min, execpromises)
+	if err != nil {
+		return err
+	}
+
+	// This variable holds the promises and is always nil.
+	var pptr unsafe.Pointer
+
+	exptr, err := syscall.BytePtrFromString(execpromises)
+	if err != nil {
+		return err
+	}
+
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(pptr), uintptr(unsafe.Pointer(exptr)), 0)
+	if e != 0 {
+		return e
+	}
+
+	return nil
+}
+
+// majmin returns major and minor version number for an OpenBSD system.
+func majmin() (major int, minor int, err error) {
+	var v Utsname
+	err = Uname(&v)
+	if err != nil {
+		return
+	}
+
+	major, err = strconv.Atoi(string(v.Release[0]))
+	if err != nil {
+		err = errors.New("cannot parse major version number returned by uname")
+		return
+	}
+
+	minor, err = strconv.Atoi(string(v.Release[2]))
+	if err != nil {
+		err = errors.New("cannot parse minor version number returned by uname")
+		return
+	}
+
+	return
+}
+
+// pledgeAvailable checks for availability of the pledge(2) syscall
+// based on the running OpenBSD version.
+func pledgeAvailable(maj, min int, execpromises string) error {
+	// If OpenBSD <= 5.9, pledge is not available.
+	if (maj == 5 && min != 9) || maj < 5 {
+		return fmt.Errorf("pledge syscall is not available on OpenBSD %d.%d", maj, min)
+	}
+
+	// If OpenBSD <= 6.2 and execpromises is not empty,
+	// return an error - execpromises is not available before 6.3
+	if (maj < 6 || (maj == 6 && min <= 2)) && execpromises != "" {
+		return fmt.Errorf("cannot use execpromises on OpenBSD %d.%d", maj, min)
+	}
+
+	return nil
+}