[PATCH v5 3/3] lib: introduce test_meminit module

Alexander Potapenko
2019-05-29T12:38:39Z

Add tests for heap and pagealloc initialization.
These can be used to check init_on_alloc and init_on_free implementations
as well as other approaches to initialization.

Expected test output in the case the kernel provides heap initialization
(e.g. when running with either init_on_alloc=1 or init_on_free=1):

test_meminit: all 10 tests in test_pages passed
test_meminit: all 40 tests in test_kvmalloc passed
test_meminit: all 60 tests in test_kmemcache passed
test_meminit: all 10 tests in test_rcu_persistent passed
test_meminit: all 120 tests passed!

Signed-off-by: Alexander Potapenko <glider@google.com>
To: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sandeep Patil <sspatil@android.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-mm@kvack.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
---
v3:
- added example test output to the description
- fixed a missing include spotted by kbuild test robot <lkp@intel.com>
- added a missing MODULE_LICENSE
- call do_kmem_cache_size() with size >= sizeof(void*) to unbreak
debug builds
v5:
- added tests for RCU slabs and __GFP_ZERO
---
lib/Kconfig.debug | 8 +
lib/Makefile | 1 +
lib/test_meminit.c | 362 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 371 insertions(+)
create mode 100644 lib/test_meminit.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cbdfae379896..085711f14abf 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2040,6 +2040,14 @@ config TEST_STACKINIT

If unsure, say N.

+config TEST_MEMINIT
+ tristate "Test heap/page initialization"
+ help
+ Test if the kernel is zero-initializing heap and page allocations.
+ This can be useful to test init_on_alloc and init_on_free features.
+
+ If unsure, say N.
+
endif # RUNTIME_TESTING_MENU

config MEMTEST
diff --git a/lib/Makefile b/lib/Makefile
index fb7697031a79..05980c802500 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -91,6 +91,7 @@ obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o
obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
+obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o

obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/

diff --git a/lib/test_meminit.c b/lib/test_meminit.c
new file mode 100644
index 000000000000..ed7efec1387b
--- /dev/null
+++ b/lib/test_meminit.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for SL[AOU]B/page initialization at alloc/free time.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
+
+#define GARBAGE_INT (0x09A7BA9E)
+#define GARBAGE_BYTE (0x9E)
+
+#define REPORT_FAILURES_IN_FN() \
+ do { \
+ if (failures) \
+ pr_info("%s failed %d out of %d times\n", \
+ __func__, failures, num_tests); \
+ else \
+ pr_info("all %d tests in %s passed\n", \
+ num_tests, __func__); \
+ } while (0)
+
+/* Calculate the number of uninitialized bytes in the buffer. */
+static int __init count_nonzero_bytes(void *ptr, size_t size)
+{
+ int i, ret = 0;
+ unsigned char *p = (unsigned char *)ptr;
+
+ for (i = 0; i < size; i++)
+ if (p[i])
+ ret++;
+ return ret;
+}
+
+/* Fill a buffer with garbage, skipping |skip| first bytes. */
+static void __init fill_with_garbage_skip(void *ptr, size_t size, size_t skip)
+{
+ unsigned int *p = (unsigned int *)ptr;
+ int i = 0;
+
+ if (skip) {
+ WARN_ON(skip > size);
+ p += skip;
+ }
+ while (size >= sizeof(*p)) {
+ p[i] = GARBAGE_INT;
+ i++;
+ size -= sizeof(*p);
+ }
+ if (size)
+ memset(&p[i], GARBAGE_BYTE, size);
+}
+
+static void __init fill_with_garbage(void *ptr, size_t size)
+{
+ fill_with_garbage_skip(ptr, size, 0);
+}
+
+static int __init do_alloc_pages_order(int order, int *total_failures)
+{
+ struct page *page;
+ void *buf;
+ size_t size = PAGE_SIZE << order;
+
+ page = alloc_pages(GFP_KERNEL, order);
+ buf = page_address(page);
+ fill_with_garbage(buf, size);
+ __free_pages(page, order);
+
+ page = alloc_pages(GFP_KERNEL, order);
+ buf = page_address(page);
+ if (count_nonzero_bytes(buf, size))
+ (*total_failures)++;
+ fill_with_garbage(buf, size);
+ __free_pages(page, order);
+ return 1;
+}
+
+/* Test the page allocator by calling alloc_pages with different orders. */
+static int __init test_pages(int *total_failures)
+{
+ int failures = 0, num_tests = 0;
+ int i;
+
+ for (i = 0; i < 10; i++)
+ num_tests += do_alloc_pages_order(i, &failures);
+
+ REPORT_FAILURES_IN_FN();
+ *total_failures += failures;
+ return num_tests;
+}
+
+/* Test kmalloc() with given parameters. */
+static int __init do_kmalloc_size(size_t size, int *total_failures)
+{
+ void *buf;
+
+ buf = kmalloc(size, GFP_KERNEL);
+ fill_with_garbage(buf, size);
+ kfree(buf);
+
+ buf = kmalloc(size, GFP_KERNEL);
+ if (count_nonzero_bytes(buf, size))
+ (*total_failures)++;
+ fill_with_garbage(buf, size);
+ kfree(buf);
+ return 1;
+}
+
+/* Test vmalloc() with given parameters. */
+static int __init do_vmalloc_size(size_t size, int *total_failures)
+{
+ void *buf;
+
+ buf = vmalloc(size);
+ fill_with_garbage(buf, size);
+ vfree(buf);
+
+ buf = vmalloc(size);
+ if (count_nonzero_bytes(buf, size))
+ (*total_failures)++;
+ fill_with_garbage(buf, size);
+ vfree(buf);
+ return 1;
+}
+
+/* Test kmalloc()/vmalloc() by allocating objects of different sizes. */
+static int __init test_kvmalloc(int *total_failures)
+{
+ int failures = 0, num_tests = 0;
+ int i, size;
+
+ for (i = 0; i < 20; i++) {
+ size = 1 << i;
+ num_tests += do_kmalloc_size(size, &failures);
+ num_tests += do_vmalloc_size(size, &failures);
+ }
+
+ REPORT_FAILURES_IN_FN();
+ *total_failures += failures;
+ return num_tests;
+}
+
+#define CTOR_BYTES (sizeof(unsigned int))
+#define CTOR_PATTERN (0x41414141)
+/* Initialize the first 4 bytes of the object. */
+static void test_ctor(void *obj)
+{
+ *(unsigned int *)obj = CTOR_PATTERN;
+}
+
+/*
+ * Check the invariants for the buffer allocated from a slab cache.
+ * If the cache has a test constructor, the first 4 bytes of the object must
+ * always remain equal to CTOR_PATTERN.
+ * If the cache isn't an RCU-typesafe one, or if the allocation is done with
+ * __GFP_ZERO, then the object contents must be zeroed after allocation.
+ * If the cache is an RCU-typesafe one, the object contents must never be
+ * zeroed after the first use. This is checked by memcmp() in
+ * do_kmem_cache_size().
+ */
+static bool __init check_buf(void *buf, int size, bool want_ctor,
+ bool want_rcu, bool want_zero)
+{
+ int bytes;
+ bool fail = false;
+
+ bytes = count_nonzero_bytes(buf, size);
+ WARN_ON(want_ctor && want_zero);
+ if (want_zero)
+ return bytes;
+ if (want_ctor) {
+ if (*(unsigned int *)buf != CTOR_PATTERN)
+ fail = 1;
+ } else {
+ if (bytes)
+ fail = !want_rcu;
+ }
+ return fail;
+}
+
+/*
+ * Test kmem_cache with given parameters:
+ * want_ctor - use a constructor;
+ * want_rcu - use SLAB_TYPESAFE_BY_RCU;
+ * want_zero - use __GFP_ZERO.
+ */
+static int __init do_kmem_cache_size(size_t size, bool want_ctor,
+ bool want_rcu, bool want_zero,
+ int *total_failures)
+{
+ struct kmem_cache *c;
+ int iter;
+ bool fail = false;
+ gfp_t alloc_mask = GFP_KERNEL | (want_zero ? __GFP_ZERO : 0);
+ void *buf, *buf_copy;
+
+ c = kmem_cache_create("test_cache", size, 1,
+ want_rcu ? SLAB_TYPESAFE_BY_RCU : 0,
+ want_ctor ? test_ctor : NULL);
+ for (iter = 0; iter < 10; iter++) {
+ buf = kmem_cache_alloc(c, alloc_mask);
+ /* Check that buf is zeroed, if it must be. */
+ fail = check_buf(buf, size, want_ctor, want_rcu, want_zero);
+ fill_with_garbage_skip(buf, size, want_ctor ? CTOR_BYTES : 0);
+ /*
+ * If this is an RCU cache, use a critical section to ensure we
+ * can touch objects after they're freed.
+ */
+ if (want_rcu) {
+ rcu_read_lock();
+ /*
+ * Copy the buffer to check that it's not wiped on
+ * free().
+ */
+ buf_copy = kmalloc(size, GFP_KERNEL);
+ if (buf_copy)
+ memcpy(buf_copy, buf, size);
+ }
+ kmem_cache_free(c, buf);
+ if (want_rcu) {
+ /*
+ * Check that |buf| is intact after kmem_cache_free().
+ * |want_zero| is false, because we wrote garbage to
+ * the buffer already.
+ */
+ fail |= check_buf(buf, size, want_ctor, want_rcu,
+ false);
+ if (buf_copy) {
+ fail |= (bool)memcmp(buf, buf_copy, size);
+ kfree(buf_copy);
+ }
+ rcu_read_unlock();
+ }
+ }
+ kmem_cache_destroy(c);
+
+ *total_failures += fail;
+ return 1;
+}
+
+/*
+ * Check that the data written to an RCU-allocated object survives
+ * reallocation.
+ */
+static int __init do_kmem_cache_rcu_persistent(int size, int *total_failures)
+{
+ struct kmem_cache *c;
+ void *buf, *buf_contents, *saved_ptr;
+ void **used_objects;
+ int i, iter, maxiter = 1024;
+ bool fail = false;
+
+ c = kmem_cache_create("test_cache", size, size, SLAB_TYPESAFE_BY_RCU,
+ NULL);
+ buf = kmem_cache_alloc(c, GFP_KERNEL);
+ saved_ptr = buf;
+ fill_with_garbage(buf, size);
+ buf_contents = kmalloc(size, GFP_KERNEL);
+ if (!buf_contents)
+ goto out;
+ used_objects = kmalloc_array(maxiter, sizeof(void *), GFP_KERNEL);
+ if (!used_objects) {
+ kfree(buf_contents);
+ goto out;
+ }
+ memcpy(buf_contents, buf, size);
+ kmem_cache_free(c, buf);
+ /*
+ * Run for a fixed number of iterations. If we never hit saved_ptr,
+ * assume the test passes.
+ */
+ for (iter = 0; iter < maxiter; iter++) {
+ buf = kmem_cache_alloc(c, GFP_KERNEL);
+ used_objects[iter] = buf;
+ if (buf == saved_ptr) {
+ fail = memcmp(buf_contents, buf, size);
+ for (i = 0; i <= iter; i++)
+ kmem_cache_free(c, used_objects[i]);
+ goto free_out;
+ }
+ }
+
+free_out:
+ kmem_cache_destroy(c);
+ kfree(buf_contents);
+ kfree(used_objects);
+out:
+ *total_failures += fail;
+ return 1;
+}
+
+/*
+ * Test kmem_cache allocation by creating caches of different sizes, with and
+ * without constructors, with and without SLAB_TYPESAFE_BY_RCU.
+ */
+static int __init test_kmemcache(int *total_failures)
+{
+ int failures = 0, num_tests = 0;
+ int i, flags, size;
+ bool ctor, rcu, zero;
+
+ for (i = 0; i < 10; i++) {
+ size = 8 << i;
+ for (flags = 0; flags < 8; flags++) {
+ ctor = flags & 1;
+ rcu = flags & 2;
+ zero = flags & 4;
+ if (ctor & zero)
+ continue;
+ num_tests += do_kmem_cache_size(size, ctor, rcu, zero,
+ &failures);
+ }
+ }
+ REPORT_FAILURES_IN_FN();
+ *total_failures += failures;
+ return num_tests;
+}
+
+/* Test the behavior of SLAB_TYPESAFE_BY_RCU caches of different sizes. */
+static int __init test_rcu_persistent(int *total_failures)
+{
+ int failures = 0, num_tests = 0;
+ int i, size;
+
+ for (i = 0; i < 10; i++) {
+ size = 8 << i;
+ num_tests += do_kmem_cache_rcu_persistent(size, &failures);
+ }
+ REPORT_FAILURES_IN_FN();
+ *total_failures += failures;
+ return num_tests;
+}
+
+/*
+ * Run the tests. Each test function returns the number of executed tests and
+ * updates |failures| with the number of failed tests.
+ */
+static int __init test_meminit_init(void)
+{
+ int failures = 0, num_tests = 0;
+
+ num_tests += test_pages(&failures);
+ num_tests += test_kvmalloc(&failures);
+ num_tests += test_kmemcache(&failures);
+ num_tests += test_rcu_persistent(&failures);
+
+ if (failures == 0)
+ pr_info("all %d tests passed!\n", num_tests);
+ else
+ pr_info("failures: %d out of %d\n", failures, num_tests);
+
+ return failures ? -EINVAL : 0;
+}
+module_init(test_meminit_init);
+
+MODULE_LICENSE("GPL");
--
2.22.0.rc1.257.g3120a18244-goog