From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Stanislawski Subject: Re: [PATCHv10 22/26] v4l: vb2-dma-contig: fail if user ptr buffer is not correctly aligned Date: Fri, 12 Oct 2012 09:44:05 +0200 Message-ID: <5077CA45.2040908@samsung.com> References: <1349880405-26049-1-git-send-email-t.stanislaws@samsung.com> <1349880405-26049-23-git-send-email-t.stanislaws@samsung.com> <2222801.pVl6O4rxaf@avalon> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-reply-to: <2222801.pVl6O4rxaf@avalon> Sender: linux-media-owner@vger.kernel.org To: Laurent Pinchart Cc: linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, airlied@redhat.com, m.szyprowski@samsung.com, kyungmin.park@samsung.com, sumit.semwal@ti.com, daeinki@gmail.com, daniel.vetter@ffwll.ch, robdclark@gmail.com, pawel@osciak.com, linaro-mm-sig@lists.linaro.org, hverkuil@xs4all.nl, remi@remlab.net, subashrp@gmail.com, mchehab@redhat.com, zhangfei.gao@gmail.com, s.nawrocki@samsung.com, k.debski@samsung.com List-Id: dri-devel@lists.freedesktop.org Hi Laurent, Thank you for the review. Please refer to the comments below. On 10/11/2012 11:36 PM, Laurent Pinchart wrote: > Hi Tomasz, > > Thanks for the patch. > > On Wednesday 10 October 2012 16:46:41 Tomasz Stanislawski wrote: >> From: Marek Szyprowski >> >> The DMA transfer must be aligned to a specific value. If userptr is not >> aligned to DMA requirements then unexpected corruptions of the memory may >> occur before or after a buffer. To prevent such situations, all unligned >> userptr buffers are rejected at VIDIOC_QBUF. >> >> Signed-off-by: Marek Szyprowski >> Acked-by: Hans Verkuil >> --- >> drivers/media/v4l2-core/videobuf2-dma-contig.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c >> b/drivers/media/v4l2-core/videobuf2-dma-contig.c index 2d661fd..571a919 >> 100644 >> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c >> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c >> @@ -493,6 +493,18 @@ static void *vb2_dc_get_userptr(void *alloc_ctx, >> unsigned long vaddr, struct vm_area_struct *vma; >> struct sg_table *sgt; >> unsigned long contig_size; >> + unsigned long dma_align = dma_get_cache_alignment(); >> + >> + /* Only cache aligned DMA transfers are reliable */ >> + if (!IS_ALIGNED(vaddr | size, dma_align)) { >> + pr_debug("user data must be aligned to %lu bytes\n", dma_align); >> + return ERR_PTR(-EINVAL); >> + } > > Looks good to me. > >> + if (!size) { >> + pr_debug("size is zero\n"); >> + return ERR_PTR(-EINVAL); >> + } > > Can this happen ? The vb2 core already has > > /* Check if the provided plane buffer is large enough */ > if (planes[plane].length < q->plane_sizes[plane]) { > ret = -EINVAL; > goto err; > } > > Unless queue_setup sets plane_sizes to 0 we can't reach vb2_dc_get_userptr. > Yes.. unfortunately, some drivers set plane_size to 0 at queue_setup. Especially, if REQBUFS is called before any S_FMT. Maybe it is just a driver bug. However, VB2 makes no sanity check if plane_sizes[] is zero. I was not able to find in Documentation nor code comments any explicit statement that plane_size cannot be zero. Therefore I have to reject reject a 0-bytes-long user pointer at vb2_dc_get_userptr before creating an empty scatterlist and passing it to the DMA layer. Regards, Tomasz Stanislawski >> buf = kzalloc(sizeof *buf, GFP_KERNEL); >> if (!buf) >