---
Changes since v2:
- Fix missing renaming of kfence_alloc_pool.
- Add __read_mostly for kfence_metadata and kfence_metadata_init.
- Use smp_store_release() and smp_load_acquire() to access kfence_metadata.
- Some tweaks to comments and git log.
v1: https://lore.kernel.org/lkml/20230710032714.26200-1-zhangpeng.00@xxxxxxxxxxxxx/
v2: https://lore.kernel.org/lkml/20230712081616.45177-1-zhangpeng.00@xxxxxxxxxxxxx/
include/linux/kfence.h | 11 ++--
mm/kfence/core.c | 124 ++++++++++++++++++++++++++++-------------
mm/kfence/kfence.h | 5 +-
mm/mm_init.c | 2 +-
4 files changed, 97 insertions(+), 45 deletions(-)
diff --git a/include/linux/kfence.h b/include/linux/kfence.h
index 726857a4b680..401af4757514 100644
--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -59,15 +59,16 @@ static __always_inline bool is_kfence_address(const void *addr)
}
/**
- * kfence_alloc_pool() - allocate the KFENCE pool via memblock
+ * kfence_alloc_pool_and_metadata() - allocate the KFENCE pool and KFENCE
+ * metadata via memblock
*/
-void __init kfence_alloc_pool(void);
+void __init kfence_alloc_pool_and_metadata(void);
/**
* kfence_init() - perform KFENCE initialization at boot time
*
- * Requires that kfence_alloc_pool() was called before. This sets up the
- * allocation gate timer, and requires that workqueues are available.
+ * Requires that kfence_alloc_pool_and_metadata() was called before. This sets
+ * up the allocation gate timer, and requires that workqueues are available.
*/
void __init kfence_init(void);
@@ -223,7 +224,7 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
#else /* CONFIG_KFENCE */
static inline bool is_kfence_address(const void *addr) { return false; }
-static inline void kfence_alloc_pool(void) { }
+static inline void kfence_alloc_pool_and_metadata(void) { }
static inline void kfence_init(void) { }
static inline void kfence_shutdown_cache(struct kmem_cache *s) { }
static inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) { return NULL; }
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index dad3c0eb70a0..6b526435886c 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -116,7 +116,15 @@ EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
* 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 __read_mostly;
+
+/*
+ * If kfence_metadata is not NULL, it may be accessed by kfence_shutdown_cache().
+ * So introduce kfence_metadata_init to initialize metadata, and then make
+ * kfence_metadata visible after initialization is successful. This prevents
+ * potential UAF or access to uninitialized metadata.
+ */
+static struct kfence_metadata *kfence_metadata_init __read_mostly;
/* Freelist with available objects. */
static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
@@ -591,7 +599,7 @@ static unsigned long kfence_init_pool(void)
__folio_set_slab(slab_folio(slab));
#ifdef CONFIG_MEMCG
- slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
+ slab->memcg_data = (unsigned long)&kfence_metadata_init[i / 2 - 1].objcg |
MEMCG_DATA_OBJCGS;
#endif
}
@@ -610,7 +618,7 @@ static unsigned long kfence_init_pool(void)
}
for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
- struct kfence_metadata *meta = &kfence_metadata[i];
+ struct kfence_metadata *meta = &kfence_metadata_init[i];
/* Initialize metadata. */
INIT_LIST_HEAD(&meta->list);
@@ -626,6 +634,12 @@ static unsigned long kfence_init_pool(void)
addr += 2 * PAGE_SIZE;
}
+ /*
+ * Make kfence_metadata visible only when initialization is successful.
+ * Otherwise, if the initialization fails and kfence_metadata is freed,
+ * it may cause UAF in kfence_shutdown_cache().
+ */
+ smp_store_release(&kfence_metadata, kfence_metadata_init);
return 0;
reset_slab:
@@ -672,26 +686,10 @@ static bool __init kfence_init_pool_early(void)
*/
memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool));
__kfence_pool = NULL;
- return false;
-}
-
-static bool kfence_init_pool_late(void)
-{
- unsigned long addr, free_size;
- addr = kfence_init_pool();
-
- if (!addr)
- return true;
+ memblock_free_late(__pa(kfence_metadata_init), KFENCE_METADATA_SIZE);
+ kfence_metadata_init = NULL;
- /* Same as above. */
- free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool);
-#ifdef CONFIG_CONTIG_ALLOC
- free_contig_range(page_to_pfn(virt_to_page((void *)addr)), free_size / PAGE_SIZE);
-#else
- free_pages_exact((void *)addr, free_size);
-#endif
- __kfence_pool = NULL;
return false;
}
@@ -841,19 +839,30 @@ static void toggle_allocation_gate(struct work_struct *work)
/* === Public interface ===================================================== */
-void __init kfence_alloc_pool(void)
+void __init kfence_alloc_pool_and_metadata(void)
{
if (!kfence_sample_interval)
return;
- /* if the pool has already been initialized by arch, skip the below. */
- if (__kfence_pool)
- return;
-
- __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
-
+ /*
+ * If the pool has already been initialized by arch, there is no need to
+ * re-allocate the memory pool.
+ */
if (!__kfence_pool)
+ __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+
+ if (!__kfence_pool) {
pr_err("failed to allocate pool\n");
+ return;
+ }
+
+ /* The memory allocated by memblock has been zeroed out. */
+ kfence_metadata_init = memblock_alloc(KFENCE_METADATA_SIZE, PAGE_SIZE);
+ if (!kfence_metadata_init) {
+ pr_err("failed to allocate metadata\n");
+ memblock_free(__kfence_pool, KFENCE_POOL_SIZE);
+ __kfence_pool = NULL;
+ }
}
static void kfence_init_enable(void)
@@ -895,33 +904,68 @@ void __init kfence_init(void)
static int kfence_init_late(void)
{
- const unsigned long nr_pages = KFENCE_POOL_SIZE / PAGE_SIZE;
+ const unsigned long nr_pages_pool = KFENCE_POOL_SIZE / PAGE_SIZE;
+ const unsigned long nr_pages_meta = KFENCE_METADATA_SIZE / PAGE_SIZE;
+ unsigned long addr = (unsigned long)__kfence_pool;
+ unsigned long free_size = KFENCE_POOL_SIZE;
+ int err = -ENOMEM;
+
#ifdef CONFIG_CONTIG_ALLOC
struct page *pages;
-
- pages = alloc_contig_pages(nr_pages, GFP_KERNEL, first_online_node, NULL);
+ pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node,
+ NULL);
if (!pages)
return -ENOMEM;
+
__kfence_pool = page_to_virt(pages);
+ pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node,
+ NULL);
+ if (pages)
+ kfence_metadata_init = page_to_virt(pages);
#else
- if (nr_pages > MAX_ORDER_NR_PAGES) {
+ if (nr_pages_pool > MAX_ORDER_NR_PAGES ||
+ nr_pages_meta > MAX_ORDER_NR_PAGES) {
pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n");
return -EINVAL;
}
+
__kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL);
if (!__kfence_pool)
return -ENOMEM;
+
+ kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL);
#endif
- if (!kfence_init_pool_late()) {
- pr_err("%s failed\n", __func__);
- return -EBUSY;
+ if (!kfence_metadata_init)
+ goto free_pool;
+
+ memzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE);
+ addr = kfence_init_pool();
+ if (!addr) {
+ kfence_init_enable();
+ kfence_debugfs_init();
+ return 0;
}
- kfence_init_enable();
- kfence_debugfs_init();
+ pr_err("%s failed\n", __func__);
+ free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool);
+ err = -EBUSY;
- return 0;
+#ifdef CONFIG_CONTIG_ALLOC
+ free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)),
+ nr_pages_meta);
+free_pool:
+ free_contig_range(page_to_pfn(virt_to_page((void *)addr)),
+ free_size / PAGE_SIZE);
+#else
+ free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE);
+free_pool:
+ free_pages_exact((void *)addr, free_size);
+#endif
+
+ kfence_metadata_init = NULL;
+ __kfence_pool = NULL;
+ return err;
}
static int kfence_enable_late(void)
@@ -941,6 +985,10 @@ void kfence_shutdown_cache(struct kmem_cache *s)
struct kfence_metadata *meta;
int i;
+ /* Pairs with release in kfence_init_pool(). */
+ if (!smp_load_acquire(&kfence_metadata))
+ return;
+
for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
bool in_use;
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index 392fb273e7bd..f46fbb03062b 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -102,7 +102,10 @@ struct kfence_metadata {
#endif
};
-extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
+#define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \
+ CONFIG_KFENCE_NUM_OBJECTS)
+
+extern struct kfence_metadata *kfence_metadata;
static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
{
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 7f7f9c677854..3d0a63c75829 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2721,7 +2721,7 @@ void __init mm_core_init(void)
*/
page_ext_init_flatmem();
mem_debugging_and_hardening_init();
- kfence_alloc_pool();
+ kfence_alloc_pool_and_metadata();
report_meminit();
kmsan_init_shadow();
stack_depot_early_init();
--
2.20.1
