[PATCH v3 0/2] test modules

[PATCH v3 0/2] test modules

[Kees Cook]

This is a pair of test modules I'd like to see in the tree. Instead
of putting these in lkdtm, where I've been adding various tests that
trigger crashes, these don't make sense there since they need to be
either distinctly separate, or their pass/fail state don't need to crash
the machine.

These live in lib/ for now, along with a few other in-kernel test modules,
and use the slightly more common "test_" naming convention, instead of
"test-". We should likely standardize on the former:

$ find . -name 'test_*.c' | grep -v /tools/ | wc -l
4
$ find . -name 'test-*.c' | grep -v /tools/ | wc -l
2

The first is entirely a no-op module, designed to allow simple testing
of the module loading and verification interface. It's useful to have
a module that has no other uses or dependencies so it can be reliably
used for just testing module loading and verification.

The second is a module that exercises the user memory access functions,
in an effort to make sure that we can quickly catch any regressions in
boundary checking (e.g. like what was recently fixed on ARM).

Thanks,

-Kees

[PATCH v3 1/2] test: add minimal module for verification testing

[Kees Cook]

When doing module loading verification tests (for example, with module
singing, or LSM hooks), it is very handy to have a module that can be
built on all systems under test, isn't auto-loaded at boot, and has
no device or similar dependencies. This creates the "test_module.ko"
module for that purpose, which only reports its load and unload to printk.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v3:
 - use KBUILD_MODNAME; Rusty Russell
v2:
 - use pr_warn, better comment, add headers explicitly, move to lib/; akpm.
---
 lib/Kconfig.debug |   14 ++++++++++++++
 lib/Makefile      |    1 +
 lib/test_module.c |   33 +++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 lib/test_module.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index db25707aa41b..81882335c625 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1578,6 +1578,20 @@ config DMA_API_DEBUG
 	  This option causes a performance degredation.  Use only if you want
 	  to debug device drivers. If unsure, say N.
 
+config TEST_MODULE
+	tristate "Test module loading with 'hello world' module"
+	default n
+	depends on m
+	help
+	  This builds the "test_module" module that emits "Hello, world"
+	  on printk when loaded. It is designed to be used for basic
+	  evaluation of the module loading subsystem (for example when
+	  validating module verification). It lacks any extra dependencies,
+	  and will not normally be loaded by the system unless explicitly
+	  requested by name.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
diff --git a/lib/Makefile b/lib/Makefile
index a459c31e8c6b..b494b9af631c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -31,6 +31,7 @@ obj-y += string_helpers.o
 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
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/test_module.c b/lib/test_module.c
new file mode 100644
index 000000000000..319b66f1ff61
--- /dev/null
+++ b/lib/test_module.c
@@ -0,0 +1,33 @@
+/*
+ * This module emits "Hello, world" on printk when loaded.
+ *
+ * It is designed to be used for basic evaluation of the module loading
+ * subsystem (for example when validating module signing/verification). It
+ * lacks any extra dependencies, and will not normally be loaded by the
+ * system unless explicitly requested by name.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+static int __init test_module_init(void)
+{
+	pr_warn("Hello, world\n");
+
+	return 0;
+}
+
+module_init(test_module_init);
+
+static void __exit test_module_exit(void)
+{
+	pr_warn("Goodbye\n");
+}
+
+module_exit(test_module_exit);
+
+MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5

Re: [PATCH v3 1/2] test: add minimal module for verification testing

[Rusty Russell]

Kees Cook <keescook@chromium.org> writes:
> When doing module loading verification tests (for example, with module
> singing, or LSM hooks), it is very handy to have a module that can be

"module singing" sounds like a horrible idea!  Is the author even
musical?  I've only heard it said David Howls.

But if my ack for the patch helps:

        Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Cheers,
Rusty.


> built on all systems under test, isn't auto-loaded at boot, and has
> no device or similar dependencies. This creates the "test_module.ko"
> module for that purpose, which only reports its load and unload to printk.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v3:
>  - use KBUILD_MODNAME; Rusty Russell
> v2:
>  - use pr_warn, better comment, add headers explicitly, move to lib/; akpm.
> ---
>  lib/Kconfig.debug |   14 ++++++++++++++
>  lib/Makefile      |    1 +
>  lib/test_module.c |   33 +++++++++++++++++++++++++++++++++
>  3 files changed, 48 insertions(+)
>  create mode 100644 lib/test_module.c
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index db25707aa41b..81882335c625 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1578,6 +1578,20 @@ config DMA_API_DEBUG
>  	  This option causes a performance degredation.  Use only if you want
>  	  to debug device drivers. If unsure, say N.
>  
> +config TEST_MODULE
> +	tristate "Test module loading with 'hello world' module"
> +	default n
> +	depends on m
> +	help
> +	  This builds the "test_module" module that emits "Hello, world"
> +	  on printk when loaded. It is designed to be used for basic
> +	  evaluation of the module loading subsystem (for example when
> +	  validating module verification). It lacks any extra dependencies,
> +	  and will not normally be loaded by the system unless explicitly
> +	  requested by name.
> +
> +	  If unsure, say N.
> +
>  source "samples/Kconfig"
>  
>  source "lib/Kconfig.kgdb"
> diff --git a/lib/Makefile b/lib/Makefile
> index a459c31e8c6b..b494b9af631c 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -31,6 +31,7 @@ obj-y += string_helpers.o
>  obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
>  obj-y += kstrtox.o
>  obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
> +obj-$(CONFIG_TEST_MODULE) += test_module.o
>  
>  ifeq ($(CONFIG_DEBUG_KOBJECT),y)
>  CFLAGS_kobject.o += -DDEBUG
> diff --git a/lib/test_module.c b/lib/test_module.c
> new file mode 100644
> index 000000000000..319b66f1ff61
> --- /dev/null
> +++ b/lib/test_module.c
> @@ -0,0 +1,33 @@
> +/*
> + * This module emits "Hello, world" on printk when loaded.
> + *
> + * It is designed to be used for basic evaluation of the module loading
> + * subsystem (for example when validating module signing/verification). It
> + * lacks any extra dependencies, and will not normally be loaded by the
> + * system unless explicitly requested by name.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +
> +static int __init test_module_init(void)
> +{
> +	pr_warn("Hello, world\n");
> +
> +	return 0;
> +}
> +
> +module_init(test_module_init);
> +
> +static void __exit test_module_exit(void)
> +{
> +	pr_warn("Goodbye\n");
> +}
> +
> +module_exit(test_module_exit);
> +
> +MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
> +MODULE_LICENSE("GPL");
> -- 
> 1.7.9.5

Re: [PATCH v3 1/2] test: add minimal module for verification testing

[Andrew Morton]

On Thu, 05 Dec 2013 13:12:17 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:

> Kees Cook <keescook@chromium.org> writes:
> > When doing module loading verification tests (for example, with module
> > singing, or LSM hooks), it is very handy to have a module that can be
> 
> "module singing" sounds like a horrible idea!  Is the author even
> musical?  I've only heard it said David Howls.

You're such a killjoy.

btw, git log | grep Singed

Re: [PATCH v3 1/2] test: add minimal module for verification testing

[Rusty Russell]

Andrew Morton <akpm@linux-foundation.org> writes:
> On Thu, 05 Dec 2013 13:12:17 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:
>
>> Kees Cook <keescook@chromium.org> writes:
>> > When doing module loading verification tests (for example, with module
>> > singing, or LSM hooks), it is very handy to have a module that can be
>> 
>> "module singing" sounds like a horrible idea!  Is the author even
>> musical?  I've only heard it said David Howls.
>
> You're such a killjoy.
>
> btw, git log | grep Singed

I had my ego singed off by Linus once, so I completely understand.

Cheers,
Rusty.

Re: [PATCH v3 1/2] test: add minimal module for verification testing

[Kees Cook]

On Wed, Dec 4, 2013 at 6:42 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> Kees Cook <keescook@chromium.org> writes:
>> When doing module loading verification tests (for example, with module
>> singing, or LSM hooks), it is very handy to have a module that can be
>
> "module singing" sounds like a horrible idea!  Is the author even

Haha, ugh. Yay for typos :)

> musical?  I've only heard it said David Howls.

*rimshot*

> But if my ack for the patch helps:
>
>         Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security

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

[Kees Cook]

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