On Thu, Nov 23, 2023 at 02:26:13PM +0800, Tang, Feng wrote: [...] > > -#ifdef CONFIG_KASAN_GENERIC > > /* > > - * KASAN could save its free meta data in object's data area at > > - * offset 0, if the size is larger than 'orig_size', it will > > - * overlap the data redzone in [orig_size+1, object_size], and > > - * the check should be skipped. > > + * KASAN can save its free meta data inside of the object at offset 0. > > + * If this meta data size is larger than 'orig_size', it will overlap > > + * the data redzone in [orig_size+1, object_size]. Thus, we adjust > > + * 'orig_size' to be as at least as big as KASAN's meta data. > > */ > > - if (kasan_metadata_size(s, true) > orig_size) > > - orig_size = s->object_size; > > -#endif > > + kasan_meta_size = kasan_metadata_size(s, true); > > + if (kasan_meta_size > orig_size) > > + orig_size = kasan_meta_size; > > 'orig_size' is to save the orignal request size for kmalloc object, > and its main purpose is to detect the memory wastage of kmalloc > objects, see commit 6edf2576a6cc "mm/slub: enable debugging memory > wasting of kmalloc" > > Setting "orig_size = s->object_size" was to skip the wastage check > and the redzone sanity check for this 'wasted space'. > > So it's better not to set 'kasan_meta_size' to orig_size. > > And from the below code, IIUC, the orig_size is not used in fixing > the boot problem found by Hyeonggon? I just tried Hyeonggon's reproducing method [1], and confirmed the below change of check_object() itself can fix the problem. [1]. https://lore.kernel.org/lkml/CAB=+i9RnOz0jDockOfw3oNageCUF5gmF+nzOzPpoTxtr7eqn7g@xxxxxxxxxxxxxx/ Thanks, Feng > > Thanks, > Feng > > > > > p += get_info_end(s); > > p += sizeof(struct track) * 2; > > @@ -1192,7 +1192,7 @@ static int check_object(struct kmem_cache *s, struct slab *slab, > > { > > u8 *p = object; > > u8 *endobject = object + s->object_size; > > - unsigned int orig_size; > > + unsigned int orig_size, kasan_meta_size; > > > > if (s->flags & SLAB_RED_ZONE) { > > if (!check_bytes_and_report(s, slab, object, "Left Redzone", > > @@ -1222,12 +1222,23 @@ static int check_object(struct kmem_cache *s, struct slab *slab, > > } > > > > if (s->flags & SLAB_POISON) { > > - if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) && > > - (!check_bytes_and_report(s, slab, p, "Poison", p, > > - POISON_FREE, s->object_size - 1) || > > - !check_bytes_and_report(s, slab, p, "End Poison", > > - p + s->object_size - 1, POISON_END, 1))) > > - return 0; > > + if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON)) { > > + /* > > + * KASAN can save its free meta data inside of the > > + * object at offset 0. Thus, skip checking the part of > > + * the redzone that overlaps with the meta data. > > + */ > > + kasan_meta_size = kasan_metadata_size(s, true); > > + if (kasan_meta_size < s->object_size - 1 && > > + !check_bytes_and_report(s, slab, p, "Poison", > > + p + kasan_meta_size, POISON_FREE, > > + s->object_size - kasan_meta_size - 1)) > > + return 0; > > + if (kasan_meta_size < s->object_size && > > + !check_bytes_and_report(s, slab, p, "End Poison", > > + p + s->object_size - 1, POISON_END, 1)) > > + return 0; > > + } > > /* > > * check_pad_bytes cleans up on its own. > > */ > > -- > > 2.25.1 > >
