Re: [PATCH 0/7] drm/msm: probe deferral fixes

[Abhinav Kumar]

Adding kuogee to this series

Hi Johan

Thanks for posting this.

We will take a look at this, re-validate and give our reviews/tested-bys.

Thanks

Abhinav
On 9/12/2022 8:40 AM, Johan Hovold wrote:
> The MSM DRM is currently broken in multiple ways with respect to probe
> deferral. Not only does the driver currently fail to probe again after a
> late deferral, but due to a related use-after-free bug this also
> triggers NULL-pointer dereferences.
>
> These bugs are not new but have become critical with the release of
> 5.19 where probe is deferred in case the aux-bus EP panel driver has not
> yet been loaded.
>
> The underlying problem is lifetime issues due to careless use of
> device-managed resources.
>
> Specifically, device-managed resources allocated post component bind
> must be tied to the lifetime of the aggregate DRM device or they will
> not necessarily be released when binding of the aggregate device is
> deferred.
>
> The following call chain and pseudo code serves as an illustration of
> the problem:
>
>   - platform_probe(pdev1)
>     - dp_display_probe()
>       - component_add()
>
>   - platform_probe(pdev2) 				// last component
>     - dp_display_probe()					// d0
>         - component_add()
>           - try_to_bring_up_aggregate_device()
> 	   - devres_open_group(adev->parent)		// d1
>
> 	   - msm_drm_bind()
> 	     - msm_drm_init()
> 	       - component_bind_all()
> 	         - for_each_component()
> 		   - component_bind()
> 		     - devres_open_group(&pdev->dev)	// d2
> 	             - dp_display_bind()
> 		       - devm_kzalloc(&pdev->dev)	// a1, OK
> 		     - devres_close_group(&pdev->dev)	// d3
>
> 	       - dpu_kms_hw_init()
> 	         - for_each_panel()
> 	           - msm_dp_modeset_init()
> 		     - dp_display_request_irq()
> 		       - devm_request_irq(&pdev->dev)	// a2, BUG
> 		     - if (pdev == pdev2 && condition)
> 		       - return -EPROBE_DEFER;
>
> 	      - if (error)
>   	        - component_unbind_all()
> 	          - for_each_component()
> 		    - component_unbind()
> 		      - dp_display_unbind()
> 		      - devres_release_group(&pdev->dev) // d4, only a1 is freed
>
>             - if (error)
> 	     - devres_release_group(adev->parent)	// d5
>
> The device-managed allocation a2 is buggy as its lifetime is tied to the
> component platform device and will not be released when the aggregate
> device bind fails (e.g. due to a probe deferral).
>
> When pdev2 is later probed again, the attempt to allocate the IRQ a
> second time will fail for pdev1 (which is still bound to its platform
> driver).
>
> This series fixes the lifetime issues by tying the lifetime of a2 (and
> similar allocations) to the lifetime of the aggregate device so that a2
> is released at d5.
>
> In some cases, such has for the DP IRQ, the above situation can also be
> avoided by moving the allocation in question to the platform driver
> probe (d0) or component bind (between d2 and d3). But as doing so is not
> a general fix, this can be done later as a cleanup/optimisation.
>
> Johan
>
>
> Johan Hovold (7):
>    drm/msm: fix use-after-free on probe deferral
>    drm/msm: fix memory corruption with too many bridges
>    drm/msm/dp: fix IRQ lifetime
>    drm/msm/dp: fix aux-bus EP lifetime
>    drm/msm/dp: fix bridge lifetime
>    drm/msm/hdmi: fix IRQ lifetime
>    drm/msm: drop modeset sanity checks
>
>   drivers/gpu/drm/bridge/parade-ps8640.c   |  2 +-
>   drivers/gpu/drm/display/drm_dp_aux_bus.c |  5 +++--
>   drivers/gpu/drm/msm/dp/dp_display.c      | 16 +++++++++-------
>   drivers/gpu/drm/msm/dp/dp_parser.c       |  6 +++---
>   drivers/gpu/drm/msm/dp/dp_parser.h       |  5 +++--
>   drivers/gpu/drm/msm/dsi/dsi.c            |  9 +++++----
>   drivers/gpu/drm/msm/hdmi/hdmi.c          |  7 ++++++-
>   drivers/gpu/drm/msm/msm_drv.c            |  1 +
>   include/drm/display/drm_dp_aux_bus.h     |  6 +++---
>   9 files changed, 34 insertions(+), 23 deletions(-)