[PATCH v3 2/2] test: check copy_to/from_user boundary validation

Kees Cook
2013-12-04T19:23:38Z

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 8404663f81d212918ff85f493649a7991209fa04 ("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>
---
v3:
- use KBUILD_MODNAME; Rusty Russell
v2:
- add sched.h for archs that define TASK_SIZE with more complexity
- add to selftests, move to lib/; akpm.
- clean up test macro, drop needless pr_warn; Joe Perches.
---
lib/Kconfig.debug | 13 ++++
lib/Makefile | 1 +
lib/test_user_copy.c | 108 +++++++++++++++++++++++++++++++++
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/user/Makefile | 13 ++++
5 files changed, 136 insertions(+)
create mode 100644 lib/test_user_copy.c
create mode 100644 tools/testing/selftests/user/Makefile

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 81882335c625..6e905cc04aa7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1592,6 +1592,19 @@ 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..b61f3e406e0b
--- /dev/null
+++ b/lib/test_user_copy.c
@@ -0,0 +1,108 @@
+/*
+ * 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;
+ 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;
+
+ /* 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((char *)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, (char *)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");
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 9f3eae290900..32487ed18354 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -9,6 +9,7 @@ TARGETS += ptrace
TARGETS += timers
TARGETS += vm
TARGETS += powerpc
+TARGETS += user

all:
for TARGET in $(TARGETS); do \
diff --git a/tools/testing/selftests/user/Makefile b/tools/testing/selftests/user/Makefile
new file mode 100644
index 000000000000..396255bd720e
--- /dev/null
+++ b/tools/testing/selftests/user/Makefile
@@ -0,0 +1,13 @@
+# Makefile for user memory selftests
+
+# No binaries, but make sure arg-less "make" doesn't trigger "run_tests"
+all:
+
+run_tests: all
+ @if /sbin/modprobe test_user_copy ; then \
+ rmmod test_user_copy; \
+ echo "user_copy: ok"; \
+ else \
+ echo "user_copy: [FAIL]"; \
+ exit 1; \
+ fi
--
1.7.9.5