kernel: Add copyin() and copyout() routines

This commit adds two new functions, copyin() and copyout() for kernel to
userspace access and vice versa. These functions ensure the userspace address
being accessed actually belongs to the process running by performing address range
checks, thereby preventing bad addresses being passed to syscalls.

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

1 files changed, 95 insertions, 0 deletions

diff --git a/sys/kern/kern_subr.c b/sys/kern/kern_subr.c
new file mode 100644
index 0000000..dd1a618
--- /dev/null
+++ b/sys/kern/kern_subr.c
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * 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 Hyra 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/system.h>
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <sys/sched.h>
+#include <vm/vm.h>
+#include <string.h>
+
+/*
+ * Check if a user address is valid.
+ *
+ * @uaddr: User address to check.
+ *
+ * Returns true if valid, otherwise false.
+ */
+static bool
+check_uaddr(uintptr_t uaddr)
+{
+    struct proc *td = this_td();
+    struct vm_range exec_range = td->addr_range[ADDR_RANGE_EXEC];
+    struct vm_range stack_range = td->addr_range[ADDR_RANGE_STACK];
+
+    if (uaddr >= exec_range.start && uaddr <= exec_range.end) {
+        return true;
+    }
+    if (uaddr >= stack_range.start && uaddr <= stack_range.end) {
+        return true;
+    }
+
+    return false;
+}
+
+/*
+ * Copy from userspace to the kernel.
+ *
+ * @uaddr: Userspace address.
+ * @kaddr: Kernelspace address.
+ * @len: Length of data.
+ */
+int
+copyin(uintptr_t uaddr, void *kaddr, size_t len)
+{
+    if (!check_uaddr(uaddr) || !check_uaddr(uaddr + len)) {
+        return -EFAULT;
+    }
+
+    memcpy(kaddr, (void *)uaddr, len);
+    return 0;
+}
+
+/*
+ * Copy from the kernel to userspace.
+ *
+ * @kaddr: Kernelspace address.
+ * @uaddr: Userspace address.
+ * @len: Length of data.
+ */
+int
+copyout(const void *kaddr, uintptr_t uaddr, size_t len)
+{
+    if (!check_uaddr(uaddr) || !check_uaddr(uaddr + len)) {
+        return -EFAULT;
+    }
+
+    memcpy((void *)uaddr, kaddr, len);
+    return 0;
+}