From: Marco Elver <elver@xxxxxxxxxx> Subject: mm, kfence: support kmem_dump_obj() for KFENCE objects 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@xxxxxxxxxx Fixes: b89fb5ef0ce6 ("mm, kfence: insert KFENCE hooks for SLUB") Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB") Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> [slab] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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(-) --- a/include/linux/kfence.h~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/include/linux/kfence.h @@ -204,6 +204,22 @@ static __always_inline __must_check bool */ 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 slab *slab); +#endif + #else /* CONFIG_KFENCE */ static inline bool is_kfence_address(const void *addr) { return false; } @@ -221,6 +237,14 @@ static inline bool __must_check kfence_h return false; } +#ifdef CONFIG_PRINTK +struct kmem_obj_info; +static inline bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) +{ + return false; +} +#endif + #endif #endif /* _LINUX_KFENCE_H */ --- a/mm/kfence/core.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/kfence/core.c @@ -231,27 +231,6 @@ static bool kfence_unprotect(unsigned lo 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; --- a/mm/kfence/kfence.h~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/kfence/kfence.h @@ -96,6 +96,27 @@ 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. */ --- a/mm/kfence/report.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/kfence/report.c @@ -273,3 +273,50 @@ void kfence_report_error(unsigned long a /* 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 slab *slab) +{ + 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_slab = slab; + 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 --- a/mm/slab.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/slab.c @@ -3665,7 +3665,7 @@ EXPORT_SYMBOL(__kmalloc_node_track_calle #endif /* CONFIG_NUMA */ #ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) { struct kmem_cache *cachep; unsigned int objnr; --- a/mm/slab_common.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/slab_common.c @@ -555,6 +555,13 @@ 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 slab *slab) +{ + if (__kfence_obj_info(kpp, object, slab)) + return; + __kmem_obj_info(kpp, object, slab); +} + /** * kmem_dump_obj - Print available slab provenance information * @object: slab object for which to find provenance information. @@ -590,6 +597,8 @@ 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) --- a/mm/slab.h~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/slab.h @@ -868,7 +868,7 @@ 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 slab *slab); +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab); #endif #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR --- a/mm/slob.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/slob.c @@ -463,7 +463,7 @@ out: } #ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) { kpp->kp_ptr = object; kpp->kp_slab = slab; --- a/mm/slub.c~mm-kfence-support-kmem_dump_obj-for-kfence-objects +++ a/mm/slub.c @@ -4312,7 +4312,7 @@ int __kmem_cache_shutdown(struct kmem_ca } #ifdef CONFIG_PRINTK -void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) +void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) { void *base; int __maybe_unused i; _
