From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D12D73AB48F; Tue, 6 Oct 2026 09:20:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791278439; cv=none; b=Sz77cS5mnGVc1U9i/+qjR9BBbkJfnHCNor18k+3/6SZpLiFkOWnPaulY3d4o7HbCsnfSS1+BiIvWYUitbjfNL/usxz2wwfQB0nAm2EwUtyny9VxjitnYrSKOYDnIDi7TL93B/mIDthIfk5Y4CBc7oF4q7wCHpREMc4oa15jfCSk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791278439; c=relaxed/simple; bh=k2v7XTUE7M2oSlV7PbZULb9YGZZnAP5BYpCfw9riwUY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nm5ISMN4SdHocjpxt60L4/uF12EMc4/2K8swjoEz3bILHTFyEHEgzncH5QV7X4UNJD0Q8z+nR42G0D/Jw647zChewS+a92gARoxb0M4tMyyVYLyZ97s4T1T1Uno+dvTBeUfS/y46kocjVDYiew1Q222k/oSlm8k+OceqX5ZaCfk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J4co+Zpc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="J4co+Zpc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7096B1F0089F; Tue, 6 Oct 2026 09:20:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791278436; bh=RRyPEkZ+ZfmK6tjBW72oAefzXONIUsLRfqoAHzypc3s=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=J4co+ZpcCJ8t4bVYxlz7ppJ19xOX2Z+P98GC60KCa3ERMO6O69lS8UC7MM18SoDvI s/Lgo1ZJuQB2Qtii2akqe1NpJ23hbjsi7E7wRXd6uwZjYPXaJW688bmmFgThgH0Bli fBhMY2nIMwW0beaDf3H9t1SM8uZHAf/aInl90KsT3wI0nEJEl1jqsh8O41wrXJ//+t KkGZJ4s0djlVAe5fowLygTFmLbQTFc7eqFy/HZAgxTo36VICiJ8IO/IPJBViINoptL x/jr+7NXYQk4EB67SCnunmjnvoURxxDMxbDMzCWh0huDtBXlE99Fx/Q1Syqk64vUaz y1BkZgYGM8J3Q== From: Kees Cook To: Vlastimil Babka Cc: Kees Cook , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, Pedro Falcato , Kuniyuki Iwashima , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next v6 6/8] mm/slab: Add tests for the existing kmem_buckets behaviour Date: Tue, 6 Oct 2026 02:20:32 -0700 Message-ID: <20261006092035.166776-6-kees@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261006092030.got.500-kees@kernel.org> References: <20261006092030.got.500-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=10322; i=kees@kernel.org; h=from:subject; bh=k2v7XTUE7M2oSlV7PbZULb9YGZZnAP5BYpCfw9riwUY=; b=owGbwMvMwCVmps19z/KJym7G02pJDFlH9iaWaF63ar82eZX4n72zhZjuJhl3ezPJP9m8XOrww rDTp4Ind5SyMIhxMciKKbIE2bnHuXi8bQ93n6sIM4eVCWQIAxenAEzk7zFGho1CehqnJk+3udFt l/BRcn2Y6Zql6tKzHpVrWiUYJK43vMLw3133yMTfGtwn007fVc7+8yRgXxv/3Hu7VDc+zuea7vN TiAEA X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit kmem_buckets has had no test coverage since it was added. Add tests, including stuff unique to the bucket design: - A bucket allocation comes from a cache of the set's own, and that cache carries SLAB_NO_MERGE. - Each size is served by a cache of the set, of the size kmalloc() rounds it up to, including 96 and 192, which are not powers of two and which kmalloc shares with a larger class on some configurations. Sizes above KMALLOC_MAX_CACHE_SIZE go to the page allocator instead, bucket set or not. - Each cache is aligned like the kmalloc cache it mirrors. - With CONFIG_SLAB_BUCKETS=n, kmem_buckets_create() still returns a non-NULL (zero size alloc pointer), so that callers only have to check for failure, and allocations through it come from the general caches. - Destroying a set takes its caches down rather than only freeing the set, which is what a module creating one on each load depends on. A set freed without its caches would leave the names taken, and the next load would warn about every one of them. This test skips when KFENCE serves its allocation, since a KFENCE object is in none of the cache's slabs for the teardown to find. The tests skip rather than compile out, which is useful for testing the CONFIG_SLAB_BUCKETS=n behaviors. Built and tests passing (with expected skips) on ARCH=x86_64 defconfig with GCC 16.2.0, with CONFIG_SLAB_BUCKETS as y and n. Assisted-by: LLM Signed-off-by: Kees Cook --- lib/tests/slub_kunit.c | 228 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 228 insertions(+) diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c index e3b63f0338d5..a2a15a49c5d7 100644 --- a/lib/tests/slub_kunit.c +++ b/lib/tests/slub_kunit.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 #include #include +#include #include #include #include @@ -9,6 +10,7 @@ #include #include #include +#include #include "../mm/slab.h" static struct kunit_resource resource; @@ -474,6 +476,227 @@ static int test_init(struct kunit *test) return 0; } +/* Destroy buckets on test exit so a failed KUNIT_ASSERT_*() doesn't leak. */ +KUNIT_DEFINE_ACTION_WRAPPER(destroy_buckets, kmem_buckets_destroy, kmem_buckets *); + +#define KUNIT_ASSERT_BUCKETS_CREATED(test, b) \ + do { \ + KUNIT_ASSERT_NOT_NULL(test, b); \ + KUNIT_ASSERT_EQ(test, 0, \ + kunit_add_action_or_reset(test, \ + destroy_buckets, b)); \ + } while (0) + +/* + * The cache an allocation came from, or NULL if it came from no cache at + * all, e.g. a size too big for any of them is served by the page allocator. + */ +static struct kmem_cache *cache_of(void *p) +{ + struct slab *slab = virt_to_slab(p); + + return slab ? slab->slab_cache : NULL; +} + +/* + * A bucket set exists to keep its allocations out of the caches everything + * else uses, so check the two things that make that true: they come from a + * cache of the set's own, and that cache is never merged into another. + */ +static void test_kmem_buckets_isolation(struct kunit *test) +{ + struct kmem_cache *bucket_cache, *general_cache; + kmem_buckets *b; + void *p, *q; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("isolated_buckets", 0, INT_MAX); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + /* + * Free each allocation before asserting on the next one: the cache + * outlives its objects, so nothing below needs them, and an assertion + * that leaves one behind would make the deferred teardown report a + * cache that is still in use. + */ + p = kmem_buckets_alloc(b, 128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + bucket_cache = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, bucket_cache); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(bucket_cache->name, "isolated_buckets-"), + "expected a bucket cache, got %s", bucket_cache->name); + + /* + * Cache merging is on by default, and a bucket cache merged into a + * same-sized general one would quietly undo the whole separation. + */ + KUNIT_EXPECT_TRUE(test, bucket_cache->flags & SLAB_NO_MERGE); + + q = kmalloc(128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, q); + general_cache = cache_of(q); + kfree(q); + KUNIT_ASSERT_NOT_NULL(test, general_cache); + + KUNIT_EXPECT_PTR_NE(test, bucket_cache, general_cache); +} + +/* + * Each size is served by a cache of the set, of the size kmalloc() rounds it + * up to, including the size classes that are not powers of two, which kmalloc + * shares with a larger class on some configurations. Sizes past the largest + * cache are served by the page allocator, bucket set or not. + */ +static void test_kmem_buckets_sizes(struct kunit *test) +{ + static const size_t sizes[] = { 8, 96, 192, 1024, 4096 }; + struct kmem_cache *c; + kmem_buckets *b; + void *p; + int i; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("sized_buckets", 0, INT_MAX); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + for (i = 0; i < ARRAY_SIZE(sizes); i++) { + p = kmem_buckets_alloc(b, sizes[i], GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "sized_buckets-"), + "size %zu: expected a bucket cache, got %s", + sizes[i], c->name); + KUNIT_EXPECT_EQ_MSG(test, c->object_size, + kmalloc_size_roundup(sizes[i]), + "size %zu: served by %s", sizes[i], c->name); + } + + /* Too big for any cache: a folio from the page allocator, not a slab. */ + p = kmem_buckets_alloc(b, KMALLOC_MAX_CACHE_SIZE + 1, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + + KUNIT_EXPECT_NULL(test, c); +} + +/* + * A bucket cache stands in for a kmalloc cache, so it has to be aligned like + * one. The DMA layer decides whether a buffer needs bouncing from its size, + * on the grounds that a kmalloc cache of that size is already aligned for + * the device, so a weaker alignment here is not something a caller can see + * coming. Without slab debugging the size implies the alignment and this + * holds either way; with it, only the cache's own alignment does. + */ +static void test_kmem_buckets_alignment(struct kunit *test) +{ + static const size_t sizes[] = { 128, 512, 2048 }; + struct kmem_cache *bucket_cache, *general_cache; + kmem_buckets *b; + void *p; + int i; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("aligned_buckets", 0, INT_MAX); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + for (i = 0; i < ARRAY_SIZE(sizes); i++) { + p = kmem_buckets_alloc(b, sizes[i], GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + bucket_cache = cache_of(p); + KUNIT_EXPECT_TRUE_MSG(test, + IS_ALIGNED((unsigned long)p, ARCH_DMA_MINALIGN), + "size %zu: object %p is not %d byte aligned", + sizes[i], p, (int)ARCH_DMA_MINALIGN); + kfree(p); + + p = kmalloc(sizes[i], GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + general_cache = cache_of(p); + kfree(p); + + KUNIT_ASSERT_NOT_NULL(test, bucket_cache); + KUNIT_ASSERT_NOT_NULL(test, general_cache); + KUNIT_EXPECT_EQ_MSG(test, bucket_cache->align, general_cache->align, + "size %zu: bucket cache aligned to %u, %s to %u", + sizes[i], bucket_cache->align, + general_cache->name, general_cache->align); + } +} + +/* + * With the feature compiled out, kmem_buckets_create() still returns + * something non-NULL so that callers only have to check for failure, and + * allocations through it work (i.e. come from the general caches). + */ +static void test_kmem_buckets_disabled(struct kunit *test) +{ + kmem_buckets *b; + struct kmem_cache *c; + void *p; + + if (IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "only meaningful without CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("disabled_buckets", 0, INT_MAX); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + p = kmem_buckets_alloc(b, 128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, !strstarts(c->name, "disabled_buckets-"), + "expected a general cache, got %s", c->name); +} + +/* Destroying a set has to take its caches down, not just free the set. */ +static void test_kmem_buckets_destroy(struct kunit *test) +{ + kmem_buckets *b; + void *p; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("destroyed_buckets", 0, INT_MAX); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + /* + * Deliberately leaked, as test_leak_destroy() leaks its own: the + * teardown below has to find it. kmem_cache_destroy() unlists the + * cache either way, so the name is still released. + */ + p = kmem_buckets_alloc(b, 128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + + /* + * A KFENCE object is in none of the cache's slabs, so the teardown + * would not find it to report. + */ + if (is_kfence_address(p)) { + kfree(p); + kunit_skip(test, "the allocation came from KFENCE"); + } + + /* Tear the set down now, rather than at exit, to check the report. */ + kunit_release_action(test, destroy_buckets, b); + + KUNIT_EXPECT_EQ(test, 2, slab_errors); +} + static struct kunit_case test_cases[] = { KUNIT_CASE(test_clobber_zone), @@ -495,6 +718,11 @@ static struct kunit_case test_cases[] = { #if defined(CONFIG_KPROBES) && defined(CONFIG_SMP) KUNIT_CASE_SLOW(test_kmalloc_nolock_and_friends_kprobe), #endif + KUNIT_CASE(test_kmem_buckets_isolation), + KUNIT_CASE(test_kmem_buckets_sizes), + KUNIT_CASE(test_kmem_buckets_alignment), + KUNIT_CASE(test_kmem_buckets_disabled), + KUNIT_CASE(test_kmem_buckets_destroy), {} }; -- 2.55.0