Message-ID: <20220124025205.329752-2-liupeng256@huawei.com>
Date:   Mon, 24 Jan 2022 02:52:03 +0000
From:   Peng Liu <liupeng256@...wei.com>
To:     <glider@...gle.com>, <elver@...gle.com>, <dvyukov@...gle.com>,
        <corbet@....net>, <sumit.semwal@...aro.org>,
        <christian.koenig@....com>, <akpm@...ux-foundation.org>
CC:     <kasan-dev@...glegroups.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linaro-mm-sig@...ts.linaro.org>,
        <linux-mm@...ck.org>, <liupeng256@...wei.com>
Subject: [PATCH RFC 1/3] kfence: Add a module parameter to adjust kfence objects

KFENCE is designed to be enabled in production kernels, but it can
be also useful in some debug situations. For machines with limited
memory and CPU resources, KASAN is really hard to run. Fortunately,
KFENCE can be a suitable candidate. For KFENCE running on a single
machine, the possibility of discovering existed bugs will increase
as the increasing of KFENCE objects, but this will cost more memory.
In order to balance the possibility of discovering existed bugs and
memory cost, KFENCE objects need to be adjusted according to memory
resources for a compiled kernel Image. Add a module parameter to
adjust KFENCE objects will make kfence to use in different machines
with the same kernel Image.

In short, the following reasons motivate us to add this parameter.
1) In some debug situations, this will make kfence flexible.
2) For some production machines with different memory and CPU size,
this will reduce the kernel-Image-version burden.

The main change is just using kfence_num_objects to replace config
CONFIG_KFENCE_NUM_OBJECTS for dynamic configuration convenient. To
make compatible, kfence_metadata and alloc_covered are alloced by
memblock_alloc. Considering "cat /sys/kernel/debug/kfence/objects"
will read kfence_metadata, the initialization of this fs should
check whether kfence_metadata is successfully allocated.

This patch (of 3):

The most important motivation of this patch series is to make
KFENCE easy-to-use in business situations.

Signed-off-by: Peng Liu <liupeng256@...wei.com>
---
 Documentation/dev-tools/kfence.rst |  14 ++--
 include/linux/kfence.h             |   3 +-
 mm/kfence/core.c                   | 108 ++++++++++++++++++++++++-----
 mm/kfence/kfence.h                 |   2 +-
 mm/kfence/kfence_test.c            |   2 +-
 5 files changed, 103 insertions(+), 26 deletions(-)

diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst
index ac6b89d1a8c3..e079dfb81dfe 100644
--- a/Documentation/dev-tools/kfence.rst
+++ b/Documentation/dev-tools/kfence.rst
@@ -41,12 +41,14 @@ guarded by KFENCE. The default is configurable via the Kconfig option
 ``CONFIG_KFENCE_SAMPLE_INTERVAL``. Setting ``kfence.sample_interval=0``
 disables KFENCE.
 
-The KFENCE memory pool is of fixed size, and if the pool is exhausted, no
-further KFENCE allocations occur. With ``CONFIG_KFENCE_NUM_OBJECTS`` (default
-255), the number of available guarded objects can be controlled. Each object
-requires 2 pages, one for the object itself and the other one used as a guard
-page; object pages are interleaved with guard pages, and every object page is
-therefore surrounded by two guard pages.
+The KFENCE memory pool size is also an important parameter, which can be
+can be set via the kernel boot parameter ``kfence.num_objects``, and if the
+pool is exhausted, no further KFENCE allocations occur. The KFENCE memory
+pool size Each object requires 2 pages, one for the object itself and the
+other one used as a guard page; object pages are interleaved with guard pages,
+and every object page is therefore surrounded by two guard pages. The default
+is configurable via the Kconfig option ``CONFIG_KFENCE_SAMPLE_INTERVAL``
+(default 255).
 
 The total memory dedicated to the KFENCE memory pool can be computed as::
 
diff --git a/include/linux/kfence.h b/include/linux/kfence.h
index 4b5e3679a72c..aec4f6b247b5 100644
--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -17,12 +17,13 @@
 #include <linux/atomic.h>
 #include <linux/static_key.h>
 
+extern unsigned long kfence_num_objects;
 /*
  * We allocate an even number of pages, as it simplifies calculations to map
  * address to metadata indices; effectively, the very first page serves as an
  * extended guard page, but otherwise has no special purpose.
  */
-#define KFENCE_POOL_SIZE ((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 * PAGE_SIZE)
+#define KFENCE_POOL_SIZE ((kfence_num_objects + 1) * 2 * PAGE_SIZE)
 extern char *__kfence_pool;
 
 DECLARE_STATIC_KEY_FALSE(kfence_allocation_key);
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 5ad40e3add45..4655bcc0306e 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -34,6 +34,9 @@
 
 #include "kfence.h"
 
+#define MIN_KFENCE_OBJECTS 1
+#define MAX_KFENCE_OBJECTS 65535
+
 /* Disables KFENCE on the first warning assuming an irrecoverable error. */
 #define KFENCE_WARN_ON(cond)                                                   \
 	({                                                                     \
@@ -93,12 +96,53 @@ module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644)
 char *__kfence_pool __ro_after_init;
 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
 
+/*
+ * The number of kfence objects will affect performance and bug detection
+ * accuracy. The initial value of this global parameter is determined by
+ * compiling settings.
+ */
+unsigned long kfence_num_objects = CONFIG_KFENCE_NUM_OBJECTS;
+EXPORT_SYMBOL(kfence_num_objects); /* Export for test modules. */
+
+static int param_set_num_objects(const char *val, const struct kernel_param *kp)
+{
+	unsigned long num;
+
+	if (system_state != SYSTEM_BOOTING)
+		return -EINVAL; /* Cannot adjust KFENCE objects number on-the-fly. */
+
+	if (kstrtoul(val, 0, &num) < 0)
+		return -EINVAL;
+
+	if (num < MIN_KFENCE_OBJECTS || num > MAX_KFENCE_OBJECTS) {
+		pr_warn("kfence_num_objects = %lu is not in valid range [%d,%d]\n",
+			num, MIN_KFENCE_OBJECTS, MAX_KFENCE_OBJECTS);
+		return -EINVAL;
+	}
+
+	*((unsigned long *)kp->arg) = num;
+	return 0;
+}
+
+static int param_get_num_objects(char *buffer, const struct kernel_param *kp)
+{
+	if (!READ_ONCE(kfence_enabled))
+		return sprintf(buffer, "0\n");
+
+	return param_get_ulong(buffer, kp);
+}
+
+static const struct kernel_param_ops num_objects_param_ops = {
+	.set = param_set_num_objects,
+	.get = param_get_num_objects,
+};
+module_param_cb(num_objects, &num_objects_param_ops, &kfence_num_objects, 0600);
+
 /*
  * Per-object metadata, with one-to-one mapping of object metadata to
  * backing pages (in __kfence_pool).
  */
-static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0);
-struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
+struct kfence_metadata *kfence_metadata;
 
 /* Freelist with available objects. */
 static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
@@ -124,11 +168,11 @@ atomic_t kfence_allocation_gate = ATOMIC_INIT(1);
  *	P(alloc_traces) = (1 - e^(-HNUM * (alloc_traces / SIZE)) ^ HNUM
  */
 #define ALLOC_COVERED_HNUM	2
-#define ALLOC_COVERED_ORDER	(const_ilog2(CONFIG_KFENCE_NUM_OBJECTS) + 2)
+#define ALLOC_COVERED_ORDER	(const_ilog2(kfence_num_objects) + 2)
 #define ALLOC_COVERED_SIZE	(1 << ALLOC_COVERED_ORDER)
 #define ALLOC_COVERED_HNEXT(h)	hash_32(h, ALLOC_COVERED_ORDER)
 #define ALLOC_COVERED_MASK	(ALLOC_COVERED_SIZE - 1)
-static atomic_t alloc_covered[ALLOC_COVERED_SIZE];
+static atomic_t *alloc_covered;
 
 /* Stack depth used to determine uniqueness of an allocation. */
 #define UNIQUE_ALLOC_STACK_DEPTH ((size_t)8)
@@ -168,7 +212,7 @@ static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);
 
 static inline bool should_skip_covered(void)
 {
-	unsigned long thresh = (CONFIG_KFENCE_NUM_OBJECTS * kfence_skip_covered_thresh) / 100;
+	unsigned long thresh = (kfence_num_objects * kfence_skip_covered_thresh) / 100;
 
 	return atomic_long_read(&counters[KFENCE_COUNTER_ALLOCATED]) > thresh;
 }
@@ -236,7 +280,7 @@ static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
 	 * error.
 	 */
 	index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
-	if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
+	if (index < 0 || index >= kfence_num_objects)
 		return NULL;
 
 	return &kfence_metadata[index];
@@ -251,7 +295,7 @@ static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *m
 
 	/* Only call with a pointer into kfence_metadata. */
 	if (KFENCE_WARN_ON(meta < kfence_metadata ||
-			   meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS))
+			   meta >= kfence_metadata + kfence_num_objects))
 		return 0;
 
 	/*
@@ -577,7 +621,7 @@ static bool __init kfence_init_pool(void)
 		addr += PAGE_SIZE;
 	}
 
-	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
+	for (i = 0; i < kfence_num_objects; i++) {
 		struct kfence_metadata *meta = &kfence_metadata[i];
 
 		/* Initialize metadata. */
@@ -638,7 +682,7 @@ DEFINE_SHOW_ATTRIBUTE(stats);
  */
 static void *start_object(struct seq_file *seq, loff_t *pos)
 {
-	if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
+	if (*pos < kfence_num_objects)
 		return (void *)((long)*pos + 1);
 	return NULL;
 }
@@ -650,7 +694,7 @@ static void stop_object(struct seq_file *seq, void *v)
 static void *next_object(struct seq_file *seq, void *v, loff_t *pos)
 {
 	++*pos;
-	if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
+	if (*pos < kfence_num_objects)
 		return (void *)((long)*pos + 1);
 	return NULL;
 }
@@ -692,7 +736,10 @@ static int __init kfence_debugfs_init(void)
 	struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL);
 
 	debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);
-	debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
+
+	/* Variable kfence_metadata may fail to allocate. */
+	if (kfence_metadata)
+		debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
 	return 0;
 }
 
@@ -756,13 +803,40 @@ static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
 
 void __init kfence_alloc_pool(void)
 {
+	phys_addr_t metadata_size;
+	phys_addr_t covered_size;
+
 	if (!kfence_sample_interval)
 		return;
 
-	__kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+	metadata_size = sizeof(struct kfence_metadata) * kfence_num_objects;
+	kfence_metadata = memblock_alloc(metadata_size, PAGE_SIZE);
+	if (!kfence_metadata) {
+		pr_err("failed to allocate metadata\n");
+		return;
+	}
 
-	if (!__kfence_pool)
+	covered_size = sizeof(atomic_t) * kfence_num_objects;
+	alloc_covered = memblock_alloc(covered_size, PAGE_SIZE);
+	if (!alloc_covered) {
+		pr_err("failed to allocate covered\n");
+		goto fail_covered;
+	}
+
+	__kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+	if (!__kfence_pool) {
 		pr_err("failed to allocate pool\n");
+		goto fail_pool;
+	}
+
+	return;
+
+fail_pool:
+	memblock_free(alloc_covered, covered_size);
+	alloc_covered = NULL;
+fail_covered:
+	memblock_free(kfence_metadata, metadata_size);
+	kfence_metadata = NULL;
 }
 
 void __init kfence_init(void)
@@ -781,8 +855,8 @@ void __init kfence_init(void)
 		static_branch_enable(&kfence_allocation_key);
 	WRITE_ONCE(kfence_enabled, true);
 	queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
-	pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
-		CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
+	pr_info("initialized - using %lu bytes for %lu objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
+		kfence_num_objects, (void *)__kfence_pool,
 		(void *)(__kfence_pool + KFENCE_POOL_SIZE));
 }
 
@@ -792,7 +866,7 @@ void kfence_shutdown_cache(struct kmem_cache *s)
 	struct kfence_metadata *meta;
 	int i;
 
-	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
+	for (i = 0; i < kfence_num_objects; i++) {
 		bool in_use;
 
 		meta = &kfence_metadata[i];
@@ -831,7 +905,7 @@ void kfence_shutdown_cache(struct kmem_cache *s)
 		}
 	}
 
-	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
+	for (i = 0; i < kfence_num_objects; i++) {
 		meta = &kfence_metadata[i];
 
 		/* See above. */
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index 2a2d5de9d379..c6d37fad977a 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -91,7 +91,7 @@ struct kfence_metadata {
 	u32 alloc_stack_hash;
 };
 
-extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
+extern struct kfence_metadata *kfence_metadata;
 
 /* KFENCE error types for report generation. */
 enum kfence_error_type {
diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index a22b1af85577..084e3a55aebb 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -623,7 +623,7 @@ static void test_gfpzero(struct kunit *test)
 			break;
 		test_free(buf2);
 
-		if (i == CONFIG_KFENCE_NUM_OBJECTS) {
+		if (i == kfence_num_objects) {
 			kunit_warn(test, "giving up ... cannot get same object back\n");
 			return;
 		}
-- 
2.18.0.huawei.25

Powered by blists - more mailing lists