commit 2dfe63e61cc31ee59ce951672b0850b5229cd5b0 upstream.

Calling kmem_obj_info() via kmem_dump_obj() on KFENCE objects has been producing garbage data due to the object not actually being maintained by SLAB or SLUB.

Fix this by implementing __kfence_obj_info() that copies relevant information to struct kmem_obj_info when the object was allocated by KFENCE; this is called by a common kmem_obj_info(), which also calls the slab/slub/slob specific variant now called __kmem_obj_info().

For completeness, kmem_dump_obj() now displays if the object was allocated by KFENCE.

Link: https://lore.kernel.org/all/20220323090520.GG16885@xsang-OptiPlex-9020/ Link: https://lkml.kernel.org/r/20220406131558.3558585-1-elver@google.com Fixes: b89fb5ef0ce6 ("mm, kfence: insert KFENCE hooks for SLUB") Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB") Signed-off-by: Marco Elver elver@google.com Reviewed-by: Hyeonggon Yoo 42.hyeyoo@gmail.com Reported-by: kernel test robot oliver.sang@intel.com Acked-by: Vlastimil Babka vbabka@suse.cz [slab] Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [elver@google.com: backport - substitute uses of struct slab with page] Signed-off-by: Marco Elver elver@google.com --- include/linux/kfence.h | 24 +++++++++++++++++++++ mm/kfence/core.c | 21 ------------------- mm/kfence/kfence.h | 21 +++++++++++++++++++ mm/kfence/report.c | 47 ++++++++++++++++++++++++++++++++++++++++++ mm/slab.c | 2 +- mm/slab.h | 2 +- mm/slab_common.c | 9 ++++++++ mm/slob.c | 2 +- mm/slub.c | 2 +- 9 files changed, 105 insertions(+), 25 deletions(-)

diff --git a/include/linux/kfence.h b/include/linux/kfence.h index 4b5e3679a72c..3c75209a545e 100644 --- a/include/linux/kfence.h +++ b/include/linux/kfence.h @@ -202,6 +202,22 @@ static __always_inline __must_check bool kfence_free(void *addr) */ bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs);

+#ifdef CONFIG_PRINTK +struct kmem_obj_info; +/** + * __kfence_obj_info() - fill kmem_obj_info struct + * @kpp: kmem_obj_info to be filled + * @object: the object + * + * Return: + * * false - not a KFENCE object + * * true - a KFENCE object, filled @kpp + * + * Copies information to @kpp for KFENCE objects. + */ +bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page); +#endif + #else /* CONFIG_KFENCE */

static inline bool is_kfence_address(const void *addr) { return false; } @@ -219,6 +235,14 @@ static inline bool __must_check kfence_handle_page_fault(unsigned long addr, boo return false; }

+#ifdef CONFIG_PRINTK +struct kmem_obj_info; +static inline bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +{ + return false; +} +#endif + #endif

#endif /* _LINUX_KFENCE_H */ diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 51ea9193cecb..86260e8f2830 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -221,27 +221,6 @@ static bool kfence_unprotect(unsigned long addr) return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false)); }

-static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) -{ - long index; - - /* The checks do not affect performance; only called from slow-paths. */ - - if (!is_kfence_address((void *)addr)) - return NULL; - - /* - * May be an invalid index if called with an address at the edge of - * __kfence_pool, in which case we would report an "invalid access" - * error. - */ - index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; - if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) - return NULL; - - return &kfence_metadata[index]; -} - static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta) { unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2; diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h index 2a2d5de9d379..92bf6eff6060 100644 --- a/mm/kfence/kfence.h +++ b/mm/kfence/kfence.h @@ -93,6 +93,27 @@ struct kfence_metadata {

extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];

+static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) +{ + long index; + + /* The checks do not affect performance; only called from slow-paths. */ + + if (!is_kfence_address((void *)addr)) + return NULL; + + /* + * May be an invalid index if called with an address at the edge of + * __kfence_pool, in which case we would report an "invalid access" + * error. + */ + index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; + if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) + return NULL; + + return &kfence_metadata[index]; +} + /* KFENCE error types for report generation. */ enum kfence_error_type { KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */ diff --git a/mm/kfence/report.c b/mm/kfence/report.c index f93a7b2a338b..37e140e7f201 100644 --- a/mm/kfence/report.c +++ b/mm/kfence/report.c @@ -273,3 +273,50 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r /* We encountered a memory safety error, taint the kernel! */ add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK); } + +#ifdef CONFIG_PRINTK +static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack) +{ + int i, j; + + i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL); + for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j) + kp_stack[j] = (void *)track->stack_entries[i]; + if (j < KS_ADDRS_COUNT) + kp_stack[j] = NULL; +} + +bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +{ + struct kfence_metadata *meta = addr_to_metadata((unsigned long)object); + unsigned long flags; + + if (!meta) + return false; + + /* + * If state is UNUSED at least show the pointer requested; the rest + * would be garbage data. + */ + kpp->kp_ptr = object; + + /* Requesting info an a never-used object is almost certainly a bug. */ + if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED)) + return true; + + raw_spin_lock_irqsave(&meta->lock, flags); + + kpp->kp_page = page; + kpp->kp_slab_cache = meta->cache; + kpp->kp_objp = (void *)meta->addr; + kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack); + if (meta->state == KFENCE_OBJECT_FREED) + kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack); + /* get_stack_skipnr() ensures the first entry is outside allocator. */ + kpp->kp_ret = kpp->kp_stack[0]; + + raw_spin_unlock_irqrestore(&meta->lock, flags); + + return true; +} +#endif diff --git a/mm/slab.c b/mm/slab.c index 03d3074d0bb0..1bd283e98c58 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3658,7 +3658,7 @@ EXPORT_SYMBOL(__kmalloc_node_track_caller); #endif /* CONFIG_NUMA */

#ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) { struct kmem_cache *cachep; unsigned int objnr; diff --git a/mm/slab.h b/mm/slab.h index 56ad7eea3ddf..1ae1bdd485c1 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -643,7 +643,7 @@ struct kmem_obj_info { void *kp_stack[KS_ADDRS_COUNT]; void *kp_free_stack[KS_ADDRS_COUNT]; }; -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page); +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page); #endif

#endif /* MM_SLAB_H */ diff --git a/mm/slab_common.c b/mm/slab_common.c index ec2bb0beed75..022319e7deaf 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -568,6 +568,13 @@ bool kmem_valid_obj(void *object) } EXPORT_SYMBOL_GPL(kmem_valid_obj);

+static void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +{ + if (__kfence_obj_info(kpp, object, page)) + return; + __kmem_obj_info(kpp, object, page); +} + /** * kmem_dump_obj - Print available slab provenance information * @object: slab object for which to find provenance information. @@ -603,6 +610,8 @@ void kmem_dump_obj(void *object) pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name); else pr_cont(" slab%s", cp); + if (is_kfence_address(object)) + pr_cont(" (kfence)"); if (kp.kp_objp) pr_cont(" start %px", kp.kp_objp); if (kp.kp_data_offset) diff --git a/mm/slob.c b/mm/slob.c index 74d3f6e60666..f3fc15df971a 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -462,7 +462,7 @@ static void slob_free(void *block, int size) }

#ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) { kpp->kp_ptr = object; kpp->kp_page = page; diff --git a/mm/slub.c b/mm/slub.c index ca6ba6bdf27b..b75eebc0350e 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -4299,7 +4299,7 @@ int __kmem_cache_shutdown(struct kmem_cache *s) }

#ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) { void *base; int __maybe_unused i;