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From:   John Stultz <john.stultz@linaro.org>
Date:   Mon, 31 Jan 2022 12:39:29 -0800
Message-ID: <CALAqxLU58UYLRNrf4C7t4_SmSa1aUVaDj4SP=zCPfb9m6HBUNw@mail.gmail.com>
Subject: Re: [PATCH] dma-buf: heaps: Fix potential spectre v1 gadget
To:     Jordy Zomer <jordy@pwning.systems>
Cc:     linux-kernel@vger.kernel.org,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>,
        Brian Starkey <Brian.Starkey@arm.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org
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On Sat, Jan 29, 2022 at 7:06 AM Jordy Zomer <jordy@pwning.systems> wrote:
>
> It appears like nr could be a Spectre v1 gadget as it's supplied by a
> user and used as an array index. Prevent the contents
> of kernel memory from being leaked to userspace via speculative
> execution by using array_index_nospec.
>
> Signed-off-by: Jordy Zomer <jordy@pwning.systems>
> ---
>  drivers/dma-buf/dma-heap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 56bf5ad01ad5..8f5848aa144f 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -14,6 +14,7 @@
>  #include <linux/xarray.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
> +#include <linux/nospec.h>
>  #include <linux/uaccess.h>
>  #include <linux/syscalls.h>
>  #include <linux/dma-heap.h>
> @@ -135,6 +136,7 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd,
>         if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
>                 return -EINVAL;
>
> +       nr = array_index_nospec(nr, ARRAY_SIZE(dma_heap_ioctl_cmds));
>         /* Get the kernel ioctl cmd that matches */
>         kcmd = dma_heap_ioctl_cmds[nr];

Thanks for submitting this! It looks sane to me.

Acked-by: John Stultz <john.stultz@linaro.org>

thanks
-john