Re: [PATCH v2] drm: Fix HDCP failures when SRM fw is missing

[Ramalingam C <ramalingam.c@intel.com>]

On 2020-04-14 at 15:02:55 -0400, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> The SRM cleanup in 79643fddd6eb2 ("drm/hdcp: optimizing the srm
> handling") inadvertently altered the behavior of HDCP auth when
> the SRM firmware is missing. Before that patch, missing SRM was
> interpreted as the device having no revoked keys. With that patch,
> if the SRM fw file is missing we reject _all_ keys.
> 
> This patch fixes that regression by returning success if the file
> cannot be found. It also checks the return value from request_srm such
> that we won't end up trying to parse the ksv list if there is an error
> fetching it.
> 
> Fixes: 79643fddd6eb ("drm/hdcp: optimizing the srm handling")
> Cc: stable@vger.kernel.org
> Cc: Ramalingam C <ramalingam.c@intel.com>
> Cc: Sean Paul <sean@poorly.run>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> 
> Changes in v2:
> -Noticed a couple other things to clean up
> ---
> 
> Sorry for the quick rev, noticed a couple other loose ends that should
> be cleaned up.
> 
>  drivers/gpu/drm/drm_hdcp.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_hdcp.c b/drivers/gpu/drm/drm_hdcp.c
> index 7f386adcf872..910108ccaae1 100644
> --- a/drivers/gpu/drm/drm_hdcp.c
> +++ b/drivers/gpu/drm/drm_hdcp.c
> @@ -241,8 +241,12 @@ static int drm_hdcp_request_srm(struct drm_device *drm_dev,
>  
>  	ret = request_firmware_direct(&fw, (const char *)fw_name,
>  				      drm_dev->dev);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		*revoked_ksv_cnt = 0;
> +		*revoked_ksv_list = NULL;
These two variables are already initialized by the caller.
> +		ret = 0;
Missing of this should have been caught by CI. May be CI system always
having the SRM file from previous execution. Never been removed. IGT
need a fix to clean the prior SRM files before execution.

CI fix shouldn't block this fix.
>  		goto exit;
> +	}
>  
>  	if (fw->size && fw->data)
>  		ret = drm_hdcp_srm_update(fw->data, fw->size, revoked_ksv_list,
> @@ -287,6 +291,8 @@ int drm_hdcp_check_ksvs_revoked(struct drm_device *drm_dev, u8 *ksvs,
>  
>  	ret = drm_hdcp_request_srm(drm_dev, &revoked_ksv_list,
>  				   &revoked_ksv_cnt);
> +	if (ret)
> +		return ret;
This error code also shouldn't effect the caller(i915) hence pushed a
change https://patchwork.freedesktop.org/series/76730/

With these addresed.

LGTM.

Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
>  
>  	/* revoked_ksv_cnt will be zero when above function failed */
>  	for (i = 0; i < revoked_ksv_cnt; i++)
> -- 
> Sean Paul, Software Engineer, Google / Chromium OS
> 
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