Re: [PATCH] drm/amd/display: Avoid HDCP over-read and corruption

[Alex Deucher]

On Fri, May 28, 2021 at 1:54 PM Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>

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
>