On 11/11/22 07:46, Feng Tang wrote:
> On Thu, Nov 10, 2022 at 04:48:35PM +0100, Vlastimil Babka wrote:
>> On 10/21/22 05:24, Feng Tang wrote:
>> > kmalloc will round up the request size to a fixed size (mostly power
>> > of 2), so there could be a extra space than what is requested, whose
>> > size is the actual buffer size minus original request size.
>> >
>> > To better detect out of bound access or abuse of this space, add
>> > redzone sanity check for it.
>> >
>> > In current kernel, some kmalloc user already knows the existence of
>> > the space and utilizes it after calling 'ksize()' to know the real
>> > size of the allocated buffer. So we skip the sanity check for objects
>> > which have been called with ksize(), as treating them as legitimate
>> > users.
>>
>> Hm so once Kees's effort is finished and all ksize() users behave correctly,
>> we can drop all that skip_orig_size_check() code, right?
>
> Yes, will update the commit log.
>
>> > In some cases, the free pointer could be saved inside the latter
>> > part of object data area, which may overlap the redzone part(for
>> > small sizes of kmalloc objects). As suggested by Hyeonggon Yoo,
>> > force the free pointer to be in meta data area when kmalloc redzone
>> > debug is enabled, to make all kmalloc objects covered by redzone
>> > check.
>> >
>> > Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
>> > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
>> > Acked-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
>>
>> Looks fine, but a suggestion below:
>>
> [...]
>> > @@ -966,13 +982,27 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
>> > static void init_object(struct kmem_cache *s, void *object, u8 val)
>> > {
>> > u8 *p = kasan_reset_tag(object);
>> > + unsigned int orig_size = s->object_size;
>> >
>> > - if (s->flags & SLAB_RED_ZONE)
>> > + if (s->flags & SLAB_RED_ZONE) {
>> > memset(p - s->red_left_pad, val, s->red_left_pad);
>> >
>> > + if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) {
>> > + orig_size = get_orig_size(s, object);
>> > +
>> > + /*
>> > + * Redzone the extra allocated space by kmalloc
>> > + * than requested.
>> > + */
>> > + if (orig_size < s->object_size)
>> > + memset(p + orig_size, val,
>> > + s->object_size - orig_size);
>>
>> Wondering if we can remove this if - memset and instead below:
>>
>> > + }
>> > + }
>> > +
>> > if (s->flags & __OBJECT_POISON) {
>> > - memset(p, POISON_FREE, s->object_size - 1);
>> > - p[s->object_size - 1] = POISON_END;
>> > + memset(p, POISON_FREE, orig_size - 1);
>> > + p[orig_size - 1] = POISON_END;
>> > }
>> >
>> > if (s->flags & SLAB_RED_ZONE)
>>
>> This continues by:
>> memset(p + s->object_size, val, s->inuse - s->object_size);
>> Instead we could do this, no?
>> memset(p + orig_size, val, s->inuse - orig_size);
>
> Yep, the code is much simpler and cleaner! thanks
>
> I also change the name from 'orig_size' to 'poison_size', as below:
>
> Thanks,
> Feng
Thanks! Now merged all to slab/for-6.2/kmalloc_redzone and for-next
