[PATCH] radeon: use kvcalloc for relocs and chunks

[Christian König]

Am 17.03.21 um 10:40 schrieb Chen Li:
> On Wed, 17 Mar 2021 17:19:11 +0800,
> Chen Li wrote:
>> On Wed, 17 Mar 2021 15:55:47 +0800,
>> Christian König wrote:
>>> Am 17.03.21 um 07:22 schrieb Chen Li:
>>>> kvmalloc_array + __GFP_ZERO is the same with kvcalloc.
>>>>
>>>> As for p->chunks, it will be used in:
>>>> ```
>>>> if (ib_chunk->kdata)
>>>> 		memcpy(parser->ib.ptr, ib_chunk->kdata, ib_chunk->length_dw * 4);
>>>> ```
>>>>
>>>> If chunks doesn't zero out with __GFP_ZERO, it may point to somewhere else, e.g.,
>>>> ```
>>>> Unable to handle kernel paging request at virtual address 0000000000010000
>>>> ...
>>>> pc is at memcpy+0x84/0x250
>>>> ra is at radeon_cs_ioctl+0x368/0xb90 [radeon]
>>>> ```
>>>>
>>>> after allocating chunks with __GFP_KERNEL/kvcalloc, this bug is fixed.
>>> NAK to zeroing the chunks array.
>>>
>>> That array should be fully initialized with data before using it, otherwise we
>>> have a much more serious bug and zeroing it out only papers over the real issue.
>>>
>>> How did you trigger the NULL pointer deref above?
>> Hi, Christian, thanks for reply! From radeon_cs_parser_init:
>> ```
>> 	if (user_chunk.chunk_id == RADEON_CHUNK_ID_IB) {
>> 			if (!p->rdev || !(p->rdev->flags & RADEON_IS_AGP))
>>
>>              /****** chenli: chunks[0] come here and continue! ******/
>>
>> 				continue;
>> 		}
>>
>> 		p->chunks[i].kdata = kvmalloc_array(size, sizeof(uint32_t), GFP_KERNEL);
>> ```
>> In my case, chunks[0] is not allocated because it is just get continued, so it's not
>> wired that kdata in "memcpy(parser->ib.ptr, ib_chunk->kdata, ib_chunk->length_dw * 4);"
>> trigger the invalid address.
>>          
> By the ways, chunks were allocated with kcalloc before https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fnext%2Flinux-next.git%2Fcommit%2F%3Fid%3D3fcb4f01deedfa290e903e030956b8e1a5cb764f&data=04%7C01%7Cchristian.koenig%40amd.com%7Ca2386f016a6f40d910a808d8e928a88f%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637515708138849091%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ztgRwRsRLV%2FUYqaWvCrQ9WGEEVh6x3a4%2FHZyS%2F%2FttBc%3D&reserved=0,
> which do zero the chunks array, that's why this error never happen before.

Ah! I was really wondering why that worked all those years.

We try to avoid kcalloc and similar in new code because it is often used 
as a wildcard to paper over real problems and disables KASAN checks 
etc... But when this is just restoring old behavior it is probably ok.

Please add a Fixes: tag pointing to the original commit which introduced 
the problem so that backporters can handle that properly.

With that done the patch is Reviewed-by: Christian König 
<christian.koenig at amd.com>

Thanks,
Christian.

>
>>> Thanks,
>>> Christian.
>>>
>>>> Signed-off-by: Chen Li <chenli at uniontech.com>
>>>> ---
>>>>    drivers/gpu/drm/radeon/radeon_cs.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/radeon/radeon_cs.c b/drivers/gpu/drm/radeon/radeon_cs.c
>>>> index fb736ef9f9aa..059431689c2d 100644
>>>> --- a/drivers/gpu/drm/radeon/radeon_cs.c
>>>> +++ b/drivers/gpu/drm/radeon/radeon_cs.c
>>>> @@ -93,8 +93,8 @@ static int radeon_cs_parser_relocs(struct radeon_cs_parser *p)
>>>>    	p->dma_reloc_idx = 0;
>>>>    	/* FIXME: we assume that each relocs use 4 dwords */
>>>>    	p->nrelocs = chunk->length_dw / 4;
>>>> -	p->relocs = kvmalloc_array(p->nrelocs, sizeof(struct radeon_bo_list),
>>>> -			GFP_KERNEL | __GFP_ZERO);
>>>> +	p->relocs = kvcalloc(p->nrelocs, sizeof(struct radeon_bo_list),
>>>> +			GFP_KERNEL);
>>>>    	if (p->relocs == NULL) {
>>>>    		return -ENOMEM;
>>>>    	}
>>>> @@ -299,7 +299,7 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
>>>>    	}
>>>>    	p->cs_flags = 0;
>>>>    	p->nchunks = cs->num_chunks;
>>>> -	p->chunks = kvmalloc_array(p->nchunks, sizeof(struct radeon_cs_chunk), GFP_KERNEL);
>>>> +	p->chunks = kvcalloc(p->nchunks, sizeof(struct radeon_cs_chunk), GFP_KERNEL);
>>>>    	if (p->chunks == NULL) {
>>>>    		return -ENOMEM;
>>>>    	}
>>>
>>>
>> Regards,
>>    Chen Li
>>
>>
> Regards,
>    Chen Li
>
>