kfence_metadata is currently a static array. For the purpose of allocating scalable __kfence_pool, we first change it to runtime allocation of metadata. Since the size of an object of kfence_metadata is 1160 bytes, we can save at least 72 pages (with default 256 objects) without enabling kfence. Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> --- 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
