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.
>
> Thanks,
> Christian.
>
> > Signed-off-by: Chen Li <chenli@xxxxxxxxxxxxx>
> > ---
> > 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
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