linux-kernel - Re: [PATCH] dma-buf: heaps: Fix potential spectre v1 gadget

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Message-ID: <CAO_48GGw3bfLdLArCMHNUsiGK_brHZ3D2dQd19wJj2_FoggCUA@mail.gmail.com>
Date:   Tue, 1 Feb 2022 13:35:12 +0530
From:   Sumit Semwal <sumit.semwal@...aro.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Jordy Zomer <jordy@...ing.systems>, linux-kernel@...r.kernel.org,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <brian.starkey@....com>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH] dma-buf: heaps: Fix potential spectre v1 gadget

Hello Jordy,

On Tue, 1 Feb 2022 at 02:09, John Stultz <john.stultz@...aro.org> wrote:
>
> On Sat, Jan 29, 2022 at 7:06 AM Jordy Zomer <jordy@...ing.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@...ing.systems>
Thanks very much for your patch; I've pushed it to drm-misc-fixes, so
we should see it in mainline soon.

> > ---
> >  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@...aro.org>
>
> thanks
> -john


Best,
Sumit.