Re: [PATCH 5/5] kasan, slub: fix conflicts with CONFIG_SLAB_FREELIST_HARDENED

[Qian Cai]

On 2/11/19 4:59 PM, Andrey Konovalov wrote:
> CONFIG_SLAB_FREELIST_HARDENED hashes freelist pointer with the address
> of the object where the pointer gets stored. With tag based KASAN we don't
> account for that when building freelist, as we call set_freepointer() with
> the first argument untagged. This patch changes the code to properly
> propagate tags throughout the loop.
> 
> Reported-by: Qian Cai <cai@xxxxxx>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
>  mm/slub.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index ce874a5c9ee7..0d32f8d30752 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -303,11 +303,6 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
>  		__p < (__addr) + (__objects) * (__s)->size; \
>  		__p += (__s)->size)
>  
> -#define for_each_object_idx(__p, __idx, __s, __addr, __objects) \
> -	for (__p = fixup_red_left(__s, __addr), __idx = 1; \
> -		__idx <= __objects; \
> -		__p += (__s)->size, __idx++)
> -
>  /* Determine object index from a given position */
>  static inline unsigned int slab_index(void *p, struct kmem_cache *s, void *addr)
>  {
> @@ -1655,17 +1650,16 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
>  	shuffle = shuffle_freelist(s, page);
>  
>  	if (!shuffle) {
> -		for_each_object_idx(p, idx, s, start, page->objects) {
> -			if (likely(idx < page->objects)) {
> -				next = p + s->size;
> -				next = setup_object(s, page, next);
> -				set_freepointer(s, p, next);
> -			} else
> -				set_freepointer(s, p, NULL);
> -		}
>  		start = fixup_red_left(s, start);
>  		start = setup_object(s, page, start);
>  		page->freelist = start;
> +		for (idx = 0, p = start; idx < page->objects - 1; idx++) {
> +			next = p + s->size;
> +			next = setup_object(s, page, next);
> +			set_freepointer(s, p, next);
> +			p = next;
> +		}
> +		set_freepointer(s, p, NULL);
>  	}
>  
>  	page->inuse = page->objects;
> 

Well, this one patch does not work here, as it throws endless errors below
during boot. Still need this patch to fix it.

https://marc.info/?l=linux-mm&m=154955366113951&w=2

[   85.744772] BUG kmemleak_object (Tainted: G    B        L   ): Freepointer
corrupt
[   85.744776]
-----------------------------------------------------------------------------
[   85.744776]
[   85.744788] INFO: Allocated in create_object+0x88/0x9c8 age=2564 cpu=153 pid=1
[   85.744797] 	kmem_cache_alloc+0x39c/0x4ec
[   85.744803] 	create_object+0x88/0x9c8
[   85.744811] 	kmemleak_alloc+0xbc/0x180
[   85.744818] 	kmem_cache_alloc+0x3ec/0x4ec
[   85.744825] 	acpi_ut_create_generic_state+0x64/0xc4
[   85.744832] 	acpi_ut_create_pkg_state+0x24/0x1c8
[   85.744840] 	acpi_ut_walk_package_tree+0x268/0x564
[   85.744848] 	acpi_ns_init_one_package+0x80/0x114
[   85.744856] 	acpi_ns_init_one_object+0x214/0x3d8
[   85.744862] 	acpi_ns_walk_namespace+0x288/0x384
[   85.744869] 	acpi_walk_namespace+0xac/0xe8
[   85.744877] 	acpi_ns_initialize_objects+0x50/0x98
[   85.744883] 	acpi_load_tables+0xac/0x120
[   85.744891] 	acpi_init+0x128/0x850
[   85.744898] 	do_one_initcall+0x3ac/0x8c0
[   85.744906] 	kernel_init_freeable+0xcdc/0x1104
[   85.744916] INFO: Freed in free_object_rcu+0x200/0x228 age=3 cpu=153 pid=0
[   85.744923] 	free_object_rcu+0x200/0x228
[   85.744931] 	rcu_process_callbacks+0xb00/0x12c0
[   85.744937] 	__do_softirq+0x644/0xfd0
[   85.744944] 	irq_exit+0x29c/0x370
[   85.744952] 	__handle_domain_irq+0xe0/0x1c4
[   85.744958] 	gic_handle_irq+0x1c4/0x3b0
[   85.744964] 	el1_irq+0xb0/0x140
[   85.744971] 	arch_cpu_idle+0x26c/0x594
[   85.744978] 	default_idle_call+0x44/0x5c
[   85.744985] 	do_idle+0x180/0x260
[   85.744993] 	cpu_startup_entry+0x24/0x28
[   85.745001] 	secondary_start_kernel+0x36c/0x440
[   85.745009] INFO: Slab 0x(____ptrval____) objects=91 used=0
fp=0x(____ptrval____) flags=0x17ffffffc000200
[   85.745015] INFO: Object 0x(____ptrval____) @offset=35296 fp=0x(____ptrval____)

kkkkk4.226750] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb
bb bb bb  ................
[   84.22[   84.226765] ORedzone (____ptrptrval____): 5a worker/223:0 Tainted: G
   B        L    5.0.0-rc6+ #36
[   84.226790] Hardware name: HPE Apollo 70             /C01_APACHE_MB         ,
BIOS L50_5.13_1.0.6 07/10/2018
[   84.226798] Workqueue: events free_obj_work
[   84.226802] Call trace:
[   84.226809]  dump_backtrace+0x0/0x450
[   84.226815]  show_stack+0x20/0x2c
[   84.226822]  __dump_stack+0x20/0x28
[   84.226828]  dump_stack+0xa0/0xfc
[   84.226835]  print_trailer+0x1a8/0x1bc
[   84.226842]  object_err+0x40/0x50
[   84.226848]  check_object+0x214/0x2b8
[   84.226854]  __free_slab+0x9c/0x31c
[   84.226860]  discard_slab+0x78/0xa8
[   84.226866]  kmem_cache_free+0x99c/0x9f0
[   84.226873]  free_obj_work+0x92c/0xa44
[   84.226879]  process_one_work+0x894/0x1280
[   84.226885]  worker_thread+0x684/0xa1c
[   84.226892]  kthread+0x2cc/0x2e8
[   84.226898]  ret_from_fork+0x10/0x18
[   84.229197]