On Wed, Jul 25, 2018 at 3:44 PM, Vincenzo Frascino@Foss
<vincenzo.frascino@xxxxxxx> wrote:
> On 06/26/2018 02:15 PM, Andrey Konovalov wrote:
>
>> @@ -325,18 +341,41 @@ void kasan_init_slab_obj(struct kmem_cache *cache,
>> const void *object)
>> void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t
>> flags)
>> {
>> - return kasan_kmalloc(cache, object, cache->object_size, flags);
>> + object = kasan_kmalloc(cache, object, cache->object_size, flags);
>> + if (IS_ENABLED(CONFIG_KASAN_HW) && unlikely(cache->ctor)) {
>> + /*
>> + * Cache constructor might use object's pointer value to
>> + * initialize some of its fields.
>> + */
>> + cache->ctor(object);
>>
> This seams breaking the kmem_cache_create() contract: "The @ctor is run when
> new pages are allocated by the cache."
> (https://elixir.bootlin.com/linux/v3.7/source/mm/slab_common.c#L83)
>
> Since there might be preexisting code relying on it, this could lead to
> global side effects. Did you verify that this is not the case?
>
> Another concern is performance related if we consider this solution suitable
> for "near-production", since with the current implementation you call the
> ctor (where present) on an object multiple times and this ends up memsetting
> and repopulating the memory every time (i.e. inode.c: inode_init_once). Do
> you know what is the performance impact?
We can assign tags to objects with constructors when a slab is
allocated and call constructors once as usual. The downside is that
such object would always have the same tag when it is reallocated, so
we won't catch use-after-frees. But that is probably something we'll
have to deal with if we're aiming for "near-production". I'll add this
change to v5, thanks!
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