test: check copy_to/from_user boundary validation

To help avoid an architecture failing to correctly check kernel/user
boundaries when handling copy_to_user, copy_from_user, put_user, or
get_user, perform some simple tests and fail to load if any of them
behave unexpectedly.

Specifically, this is to make sure there is a way to notice if things
like what was fixed in commit 8404663f81d2 ("ARM: 7527/1: uaccess:
explicitly check __user pointer when !CPU_USE_DOMAINS") ever regresses
again, for any architecture.

Additionally, adds new "user" selftest target, which loads this module.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 124 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7e37a36b6913..e0e2eebf7ab3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1609,6 +1609,19 @@ config TEST_MODULE
 
           If unsure, say N.
 
+config TEST_USER_COPY
+        tristate "Test user/kernel boundary protections"
+        default n
+        depends on m
+        help
+          This builds the "test_user_copy" module that runs sanity checks
+          on the copy_to/from_user infrastructure, making sure basic
+          user/kernel boundary testing is working. If it fails to load,
+          a regression has been detected in the user/kernel memory boundary
+          protections.
+
+          If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
diff --git a/lib/Makefile b/lib/Makefile
index b494b9af631c..98ec3b861062 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_MODULE) += test_module.o
+obj-$(CONFIG_TEST_USER_COPY) += test_user_copy.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
new file mode 100644
index 000000000000..0ecef3e4690e
--- /dev/null
+++ b/lib/test_user_copy.c
@@ -0,0 +1,110 @@
+/*
+ * Kernel module for testing copy_to/from_user infrastructure.
+ *
+ * Copyright 2013 Google Inc. All Rights Reserved
+ *
+ * Authors:
+ *      Kees Cook       <keescook@chromium.org>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/mman.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+
+#define test(condition, msg)            \
+({                                      \
+        int cond = (condition);         \
+        if (cond)                       \
+                pr_warn("%s\n", msg);   \
+        cond;                           \
+})
+
+static int __init test_user_copy_init(void)
+{
+        int ret = 0;
+        char *kmem;
+        char __user *usermem;
+        char *bad_usermem;
+        unsigned long user_addr;
+        unsigned long value = 0x5A;
+
+        kmem = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
+        if (!kmem)
+                return -ENOMEM;
+
+        user_addr = vm_mmap(NULL, 0, PAGE_SIZE * 2,
+                            PROT_READ | PROT_WRITE | PROT_EXEC,
+                            MAP_ANONYMOUS | MAP_PRIVATE, 0);
+        if (user_addr >= (unsigned long)(TASK_SIZE)) {
+                pr_warn("Failed to allocate user memory\n");
+                kfree(kmem);
+                return -ENOMEM;
+        }
+
+        usermem = (char __user *)user_addr;
+        bad_usermem = (char *)user_addr;
+
+        /* Legitimate usage: none of these should fail. */
+        ret |= test(copy_from_user(kmem, usermem, PAGE_SIZE),
+                    "legitimate copy_from_user failed");
+        ret |= test(copy_to_user(usermem, kmem, PAGE_SIZE),
+                    "legitimate copy_to_user failed");
+        ret |= test(get_user(value, (unsigned long __user *)usermem),
+                    "legitimate get_user failed");
+        ret |= test(put_user(value, (unsigned long __user *)usermem),
+                    "legitimate put_user failed");
+
+        /* Invalid usage: none of these should succeed. */
+        ret |= test(!copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
+                                    PAGE_SIZE),
+                    "illegal all-kernel copy_from_user passed");
+        ret |= test(!copy_from_user(bad_usermem, (char __user *)kmem,
+                                    PAGE_SIZE),
+                    "illegal reversed copy_from_user passed");
+        ret |= test(!copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
+                                  PAGE_SIZE),
+                    "illegal all-kernel copy_to_user passed");
+        ret |= test(!copy_to_user((char __user *)kmem, bad_usermem,
+                                  PAGE_SIZE),
+                    "illegal reversed copy_to_user passed");
+        ret |= test(!get_user(value, (unsigned long __user *)kmem),
+                    "illegal get_user passed");
+        ret |= test(!put_user(value, (unsigned long __user *)kmem),
+                    "illegal put_user passed");
+
+        vm_munmap(user_addr, PAGE_SIZE * 2);
+        kfree(kmem);
+
+        if (ret == 0) {
+                pr_info("tests passed.\n");
+                return 0;
+        }
+
+        return -EINVAL;
+}
+
+module_init(test_user_copy_init);
+
+static void __exit test_user_copy_exit(void)
+{
+        pr_info("unloaded.\n");
+}
+
+module_exit(test_user_copy_exit);
+
+MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
+MODULE_LICENSE("GPL");