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

[Sean Paul]

On Wed, Apr 29, 2020 at 9:50 AM Ramalingam C <ramalingam.c at intel.com> wrote:
>
> On 2020-04-14 at 15:02:55 -0400, Sean Paul wrote:
> > From: Sean Paul <seanpaul at 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 at vger.kernel.org
> > Cc: Ramalingam C <ramalingam.c at intel.com>
> > Cc: Sean Paul <sean at poorly.run>
> > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > Cc: Maxime Ripard <mripard at kernel.org>
> > Cc: Thomas Zimmermann <tzimmermann at suse.de>
> > Cc: David Airlie <airlied at linux.ie>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Cc: dri-devel at lists.freedesktop.org
> > Signed-off-by: Sean Paul <seanpaul at 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.

Right now it is, but that's not guaranteed. In the ret == 0 case, it's
pretty common for a caller to assume the called function has
validated/assigned all the function output.

> > +             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)

Why not? I'd assume an invalid SRM revocation list should probably be
treated as failure?


> hence pushed a
> change https://patchwork.freedesktop.org/series/76730/
>
> With these addresed.
>
> LGTM.
>
> Reviewed-by: Ramalingam C <ramalingam.c at 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
> >