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Date: Fri, 7 Jun 2019 08:35:42 -0700
From: Kees Cook <keescook@...omium.org>
To: Alexander Potapenko <glider@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Sandeep Patil <sspatil@...roid.com>,
Laura Abbott <labbott@...hat.com>, Jann Horn <jannh@...gle.com>,
Marco Elver <elver@...gle.com>, linux-mm@...ck.org,
linux-security-module@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v6 3/3] lib: introduce test_meminit module
On Thu, Jun 06, 2019 at 06:48:45PM +0200, Alexander Potapenko wrote:
> 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@...gle.com>
Acked-by: Kees Cook <keescook@...omium.org>
-Kees
> To: Kees Cook <keescook@...omium.org>
> To: Andrew Morton <akpm@...ux-foundation.org>
> To: Christoph Lameter <cl@...ux.com>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Kostya Serebryany <kcc@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Sandeep Patil <sspatil@...roid.com>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Marco Elver <elver@...gle.com>
> Cc: linux-mm@...ck.org
> Cc: linux-security-module@...r.kernel.org
> Cc: kernel-hardening@...ts.openwall.com
> ---
> v3:
> - added example test output to the description
> - fixed a missing include spotted by kbuild test robot <lkp@...el.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.rc1.311.g5d7573a151-goog
>
--
Kees Cook
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