On 4/4/22 10:10, Marco Elver wrote: > On Mon, Apr 04, 2022 at 12:05PM +0900, Hyeonggon Yoo wrote: > (Maybe CONFIG_KCSAN_STRICT=y is going to yield something? I still doubt > it thought, this bug is related to corrupted stackdepot handle > somewhere...) > >> I noticed that it is not reproduced when KASAN=y and KFENCE=n (reproduced 0 of 181). >> and it was reproduced 56 of 196 when KASAN=n and KFENCE=y >> >> maybe this issue is related to kfence? Hmm kfence seems to be a good lead. If I understand kfence_guarded_alloc() correctly, it tries to set up something that really looks like a normal slab page? Especially the part with comment /* Set required slab fields. */ But it doesn't seem to cover the debugging parts that SLUB sets up with alloc_debug_processing(). This includes alloc stack saving, thus, after commit 555b8c8cb3, a stackdepot handle setting. It probably normally doesn't matter as is_kfence_address() redirects processing of kfence-allocated objects so we don't hit any slub code that expects the debugging parts to be properly initialized. But here we are in mem_dump_obj() -> kmem_dump_obj() -> kmem_obj_info(). Because kmem_valid_obj() returned true, fooled by folio_test_slab() returning true because of the /* Set required slab fields. */ code. Yet the illusion is not perfect and we read garbage instead of a valid stackdepot handle. IMHO we should e.g. add the appropriate is_kfence_address() test into kmem_valid_obj(), to exclude kfence-allocated objects? Sounds much simpler than trying to extend the illusion further to make kmem_dump_obj() work? Instead kfence could add its own specific handler to mem_dump_obj() to print its debugging data? > What about KASAN=n and KFENCE=n? > > Thanks, > -- Marco
