kern: security: Add initial support for MAC

This commit introduces initial support for mandatory access control. As
one may recall, L5 follows "everything is memory". In order to interact
with a resource, a process must request it from the kernel in the form
of a (sometimes) syncable memory buffer.

Each resource as well as processes have an access level, if a process
attempts to request a resource with a higher access level than it, the
request is rejected by the kernel. However, if a process has a greater
than or equal access level as a resource, the request can be granted.

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/src/sys/compat/unix/os/os_mac.c b/src/sys/compat/unix/os/os_mac.c
new file mode 100644
index 0000000..8180090
--- /dev/null
+++ b/src/sys/compat/unix/os/os_mac.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/syscall.h>
+#include <sys/proc.h>
+#include <sys/errno.h>
+#include <sys/types.h>
+#include <os/mac.h>
+#include <compat/unix/syscall.h>
+
+/*
+ * ARG0: Border ID (BORDER_*)
+ * ARG1: Length requested
+ * ARG2: Offset requested
+ * ARG3: Flags
+ * ARG4: Result
+ */
+scret_t
+sys_cross(struct syscall_args *scargs)
+{
+    border_id_t bd = SCARG(scargs, border_id_t, 0);
+    size_t len = SCARG(scargs, size_t, 1);
+    off_t off = SCARG(scargs, off_t, 2);
+    int flags = SCARG(scargs, int, 3);
+    void **res = SCARG(scargs, void **, 4);
+    struct mac_border *bop;
+    struct proc *self = proc_self();
+    int error;
+
+    error = proc_check_addr(self, (uintptr_t)res, len);
+    if (error < 0) {
+        return error;
+    }
+
+    bop = mac_get_border(bd);
+    if (bop == NULL) {
+        return -EIO;
+    }
+
+    return mac_map(bop, off, len, res, flags);
+}