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References: <20211216161603.983711-1-steven.price@arm.com>
In-Reply-To: <20211216161603.983711-1-steven.price@arm.com>
From:   Rob Herring <robh@kernel.org>
Date:   Thu, 16 Dec 2021 11:12:42 -0600
Message-ID: <CAL_JsqKZBsJxy8h5EQf0wwfioWS-Kx9i=0cQ7p4FHckEXstGiw@mail.gmail.com>
Subject: Re: [PATCH] drm/panfrost: Avoid user size passed to kvmalloc()
To:     Steven Price <steven.price@arm.com>
Cc:     Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>
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On Thu, Dec 16, 2021 at 10:16 AM Steven Price <steven.price@arm.com> wrote:
>
> panfrost_copy_in_sync() takes the number of fences from user space
> (in_sync_count) and used to kvmalloc() an array to hold that number of
> fences before processing them. This provides an easy method for user
> space to trigger the OOM killer (by temporarily allocating large amounts
> of kernel memory) or hit the WARN_ONCE() added by 7661809d493b ("mm:
> don't allow oversized kvmalloc() calls").
>
> Since we don't expect there to be a large number of fences we can
> instead iterate over the fences one-by-one and avoid the temporary
> allocation altogether. This also makes the code simpler.

Doesn't the BO lookup suffer from the same issue?

Rob