Re: [Intel-gfx] [PATCH] drm/i915/display: Fix a use-after-free when intel_edp_init_connector fails

[Imre Deak <imre.deak@intel.com>]

On Tue, Dec 20, 2022 at 02:40:47PM +0200, Jani Nikula wrote:
> On Tue, 20 Dec 2022, Maarten Lankhorst <maarten.lankhorst@linux.intel.com> wrote:
> > We enable the DP aux channel during probe, but may free the connector
> > soon afterwards. Ensure the DP aux display power put is completed before
> > everything is freed, to prevent a use-after-free in icl_aux_pw_to_phy(),
> > called from icl_combo_phy_aux_power_well_disable.
> 
> Feels like the placement of the intel_display_power_flush_work_sync()
> call in intel_dp_aux_fini() is a bit arbitrary.
> 
> If we add it in intel_dp_aux_fini(), the async and sync waits will both
> be called on the regular encoder destroy path.

Yes, calling intel_display_power_flush_work() from the error handler at
the end of intel_dp_init_connector() would be better.

> Maybe both intel_ddi_encoder_destroy() and intel_dp_encoder_destroy()
> should call intel_display_power_flush_work_sync(), instead of async,

intel_display_power_flush_work() ensures that power wells without a
reference held are disabled when it returns, so no need to call the
_sync() version for encoders (the _sync() version ensures in addition
during driver unloading that the work function is not running).

> and maybe the error paths should call those functions instead of just
> drm_encoder_cleanup()?

Yes, the cleanup in those functions could be shared with the error
handling in g4x_dp_init() and intel_ddi_init(), except kfree(dig_port)
which also happens if drm_encoder_init() fails. 

For this intel_pps_vdd_off_sync() / intel_dp_aux_fini() would also
happen later at the end of g4x_dp_init()/intel_ddi_init(), I guess
that's ok.

I wonder if not handling drm_encoder_init() error in intel_ddi_init()
was on purpose, can't see a reason for it.

> Imre?
> 
> 
> BR,
> Jani.
> 
> 
> >
> > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_display_power.c | 2 +-
> >  drivers/gpu/drm/i915/display/intel_display_power.h | 1 +
> >  drivers/gpu/drm/i915/display/intel_dp_aux.c        | 2 ++
> >  3 files changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_power.c b/drivers/gpu/drm/i915/display/intel_display_power.c
> > index 04915f85a0df..0edb5532461f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_power.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_power.c
> > @@ -776,7 +776,7 @@ void intel_display_power_flush_work(struct drm_i915_private *i915)
> >   * Like intel_display_power_flush_work(), but also ensure that the work
> >   * handler function is not running any more when this function returns.
> >   */
> > -static void
> > +void
> >  intel_display_power_flush_work_sync(struct drm_i915_private *i915)
> >  {
> >  	struct i915_power_domains *power_domains = &i915->display.power.domains;
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_power.h b/drivers/gpu/drm/i915/display/intel_display_power.h
> > index 7136ea3f233e..dc10ee0519e6 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_power.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_power.h
> > @@ -188,6 +188,7 @@ void __intel_display_power_put_async(struct drm_i915_private *i915,
> >  				     enum intel_display_power_domain domain,
> >  				     intel_wakeref_t wakeref);
> >  void intel_display_power_flush_work(struct drm_i915_private *i915);
> > +void intel_display_power_flush_work_sync(struct drm_i915_private *i915);
> >  #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_RUNTIME_PM)
> >  void intel_display_power_put(struct drm_i915_private *dev_priv,
> >  			     enum intel_display_power_domain domain,
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > index f1835c74bff0..1006dddad2d5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > @@ -680,6 +680,8 @@ void intel_dp_aux_fini(struct intel_dp *intel_dp)
> >  	if (cpu_latency_qos_request_active(&intel_dp->pm_qos))
> >  		cpu_latency_qos_remove_request(&intel_dp->pm_qos);
> >  
> > +	/* Ensure async work from intel_dp_aux_xfer() is flushed before we clean up */
> > +	intel_display_power_flush_work_sync(dp_to_i915(intel_dp));
> >  	kfree(intel_dp->aux.name);
> >  }
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center