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References: <20210528175354.790719-1-keescook@chromium.org>
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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 1 Jun 2021 22:06:11 -0400
Message-ID: <CADnq5_PsvOqBW4-WDvR7BqaZgq3R8vYRPz2=c+87Dokk-zWz_A@mail.gmail.com>
Subject: Re: [PATCH] drm/amd/display: Avoid HDCP over-read and corruption
To:     Kees Cook <keescook@chromium.org>
Cc:     Alex Deucher <alexander.deucher@amd.com>,
        Martin Tsai <martin.tsai@amd.com>, Leo Li <sunpeng.li@amd.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Wenjing Liu <wenjing.liu@amd.com>,
        Anson Jacob <Anson.Jacob@amd.com>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Wheeler <daniel.wheeler@amd.com>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Bindu Ramamurthy <bindu.r@amd.com>
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On Fri, May 28, 2021 at 1:54 PM Kees Cook <keescook@chromium.org> wrote:
>
> Instead of reading the desired 5 bytes of the actual target field,
> the code was reading 8. This could result in a corrupted value if the
> trailing 3 bytes were non-zero, so instead use an appropriately sized
> and zero-initialized bounce buffer, and read only 5 bytes before casting
> to u64.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Applied.  Thanks!

> ---
>  drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
> index 2cbd931363bd..6d26d9c63ab2 100644
> --- a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
> +++ b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
> @@ -29,8 +29,10 @@ static inline enum mod_hdcp_status validate_bksv(struct mod_hdcp *hdcp)
>  {
>         uint64_t n = 0;
>         uint8_t count = 0;
> +       u8 bksv[sizeof(n)] = { };
>
> -       memcpy(&n, hdcp->auth.msg.hdcp1.bksv, sizeof(uint64_t));
> +       memcpy(bksv, hdcp->auth.msg.hdcp1.bksv, sizeof(hdcp->auth.msg.hdcp1.bksv));
> +       n = *(uint64_t *)bksv;
>
>         while (n) {
>                 count++;
> --
> 2.25.1
>