Messages in this thread | | | Date | Sun, 24 Jul 2022 20:24:41 +0200 | Subject | Re: [PATCH] drm: Prevent modeset helpers to access an uninitialized drm_mode_config | From | Thomas Zimmermann <> |
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Hi Javier
Am 24.07.22 um 14:37 schrieb Javier Martinez Canillas: > DRM drivers initialize the mode configuration with drmm_mode_config_init() > and that function (among other things) initializes mutexes that are later > used by modeset helpers. > > But the helpers should only attempt to grab those locks if the mode config > was properly initialized. Otherwise it can lead to kernel oops. An example > is when a DRM driver using the component framework does not initialize the > drm_mode_config, because its .bind callback was not being executed due one > of its expected sub-devices' driver failing to probe. > > Some drivers check the struct drm_driver.registered field as an indication > on whether their .shutdown callback should call helpers to tearn down the > mode configuration or not, but most drivers just assume that it is always > safe to call helpers such as drm_atomic_helper_shutdown() during shutdown. > > Let make the DRM core more robust and prevent this to happen, by marking a > struct drm_mode_config as initialized during drmm_mode_config_init(). that > way helpers can check for it and not attempt to grab uninitialized mutexes.
I disagree. This patch looks like cargo-cult programming and entirely arbitrary. The solution here is to fix drivers. The actual test to perform is to instrument the mutex implementation to detect uninitialized mutexes.
Best regards Thomas
> > Signed-off-by: Javier Martinez Canillas <javierm@redhat.com> > --- > > drivers/gpu/drm/drm_mode_config.c | 4 ++++ > drivers/gpu/drm/drm_modeset_lock.c | 6 ++++++ > include/drm/drm_mode_config.h | 8 ++++++++ > 3 files changed, 18 insertions(+) > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c > index 59b34f07cfce..db649f97120b 100644 > --- a/drivers/gpu/drm/drm_mode_config.c > +++ b/drivers/gpu/drm/drm_mode_config.c > @@ -456,6 +456,8 @@ int drmm_mode_config_init(struct drm_device *dev) > dma_resv_fini(&resv); > } > > + dev->mode_config.initialized = true; > + > return drmm_add_action_or_reset(dev, drm_mode_config_init_release, > NULL); > } > @@ -549,6 +551,8 @@ void drm_mode_config_cleanup(struct drm_device *dev) > idr_destroy(&dev->mode_config.tile_idr); > idr_destroy(&dev->mode_config.object_idr); > drm_modeset_lock_fini(&dev->mode_config.connection_mutex); > + > + dev->mode_config.initialized = false; > } > EXPORT_SYMBOL(drm_mode_config_cleanup); > > diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c > index 918065982db4..d6a81cb88123 100644 > --- a/drivers/gpu/drm/drm_modeset_lock.c > +++ b/drivers/gpu/drm/drm_modeset_lock.c > @@ -444,6 +444,9 @@ EXPORT_SYMBOL(drm_modeset_unlock); > * > * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() > * > + * This function must only be called after drmm_mode_config_init(), since it > + * takes locks that are initialized as part of the initial mode configuration. > + * > * Returns: 0 on success or a negative error-code on failure. > */ > int drm_modeset_lock_all_ctx(struct drm_device *dev, > @@ -454,6 +457,9 @@ int drm_modeset_lock_all_ctx(struct drm_device *dev, > struct drm_plane *plane; > int ret; > > + if (WARN_ON(!dev->mode_config.initialized)) > + return -EINVAL; > + > ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); > if (ret) > return ret; > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h > index 6b5e01295348..d2e1a6d7dcc2 100644 > --- a/include/drm/drm_mode_config.h > +++ b/include/drm/drm_mode_config.h > @@ -954,6 +954,14 @@ struct drm_mode_config { > struct drm_atomic_state *suspend_state; > > const struct drm_mode_config_helper_funcs *helper_private; > + > + /** > + * @initialized: > + * > + * Internally used by modeset helpers such as drm_modeset_lock_all_ctx() > + * to determine if the mode configuration has been properly initialized. > + */ > + bool initialized; > }; > > int __must_check drmm_mode_config_init(struct drm_device *dev);
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev [unhandled content-type:application/pgp-signature] | |