linux-kernel - Re: [PATCH 26/43] kmsan: virtio: check/unpoison scatterlist in vring_map_one

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Date:   Thu, 6 Jan 2022 07:46:37 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/43] kmsan: virtio: check/unpoison scatterlist in
 vring_map_one_sg()

On Tue, Dec 14, 2021 at 05:20:33PM +0100, Alexander Potapenko wrote:
> If vring doesn't use the DMA API, KMSAN is unable to tell whether the
> memory is initialized by hardware. Explicitly call kmsan_handle_dma()
> from vring_map_one_sg() in this case to prevent false positives.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>

OK I guess

Acked-by: Michael S. Tsirkin <mst@...hat.com>

IIUC this depends on the rest of the patchset, so feel free to
merge.

> ---
> Link: https://linux-review.googlesource.com/id/I211533ecb86a66624e151551f83ddd749536b3af
> ---
>  drivers/virtio/virtio_ring.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 6d2614e34470f..bf4d5b331e99d 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -11,6 +11,7 @@
>  #include <linux/module.h>
>  #include <linux/hrtimer.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/kmsan-checks.h>
>  #include <linux/spinlock.h>
>  #include <xen/xen.h>
>  
> @@ -331,8 +332,15 @@ static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
>  				   struct scatterlist *sg,
>  				   enum dma_data_direction direction)
>  {
> -	if (!vq->use_dma_api)
> +	if (!vq->use_dma_api) {
> +		/*
> +		 * If DMA is not used, KMSAN doesn't know that the scatterlist
> +		 * is initialized by the hardware. Explicitly check/unpoison it
> +		 * depending on the direction.
> +		 */
> +		kmsan_handle_dma(sg_page(sg), sg->offset, sg->length, direction);
>  		return (dma_addr_t)sg_phys(sg);
> +	}
>  
>  	/*
>  	 * We can't use dma_map_sg, because we don't use scatterlists in
> -- 
> 2.34.1.173.g76aa8bc2d0-goog