[PATCH v2] drm/ast: Fix potential NULL-pointer read during atomic mode setting

Daniel Vetter daniel at ffwll.ch
Wed Nov 27 10:49:27 UTC 2019 

On Wed, Nov 27, 2019 at 08:31:09AM +0100, Thomas Zimmermann wrote:
> When enabling the CRTC after waking up from a power-saving mode, the
> primary plane's framebuffer might be NULL, which leads to a stack trace
> as shown below.
> 
>   [  632.624608] BUG: kernel NULL pointer dereference, address: 0000000000000048
>   [  632.624631] #PF: supervisor read access in kernel mode
>   [  632.624639] #PF: error_code(0x0000) - not-present page
>   [  632.624647] PGD 0 P4D 0
>   [  632.624654] Oops: 0000 [#1] SMP PTI
>   [  632.624662] CPU: 0 PID: 2082 Comm: gnome-shell Tainted: G            E     5.4.0-rc7-1-default+ #114
>   [  632.624673] Hardware name: Sun Microsystems SUN FIRE X2270 M2/SUN FIRE X2270 M2, BIOS 2.05    07/01/2010
>   [  632.624689] RIP: 0010:ast_crtc_helper_atomic_enable+0x7d/0x680 [ast]
>   [  632.624698] Code: 48 8b 80 e0 02 00 00 4c 8b 60 10 31 c0 f3 48 ab 48 8b 83 78 04 00 00 4c 89 ef 48 8d 70 18 e8 9a e9 55 ce 48 8b 83 78 04 00 00 <49> 8b 7c 24 48 4c 89 ea 4c 8d 44 24 28 48 8d 4c 24 20 48 8d 70 18
>   [  632.624718] RSP: 0018:ffffbe9ec123fa40 EFLAGS: 00010246
>   [  632.624726] RAX: ffff95a13cfd3400 RBX: ffff95a13cf32000 RCX: 0000000000000000
>   [  632.624735] RDX: 0000000000000000 RSI: ffff95a13cfd34e8 RDI: ffffbe9ec123fb40
>   [  632.624744] RBP: ffffbe9ec123fb80 R08: 0000000000000000 R09: 0000000000000003
>   [  632.624753] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>   [  632.624762] R13: ffffbe9ec123fa70 R14: ffff95a13beb7000 R15: ffff95a13cf32800
>   [  632.624772] FS:  00007f6d2763e140(0000) GS:ffff95a134000000(0000) knlGS:0000000000000000
>   [  632.624782] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [  632.624790] CR2: 0000000000000048 CR3: 00000001192f8004 CR4: 00000000000206f0
>   [  632.624800] Call Trace:
>   [  632.624811]  ? __lock_acquire+0x409/0x7c0
>   [  632.624830]  drm_atomic_helper_commit_modeset_enables+0x1af/0x200
>   [  632.624840]  drm_atomic_helper_commit_tail+0x32/0x70
>   [  632.624849]  commit_tail+0xc7/0x110
>   [  632.624857]  drm_atomic_helper_commit+0x121/0x130
>   [  632.624867]  drm_atomic_connector_commit_dpms+0xd7/0x100
>   [  632.624878]  set_property_atomic+0xaf/0x110
>   [  632.624890]  drm_mode_obj_set_property_ioctl+0xbb/0x190
>   [  632.624899]  ? drm_mode_obj_find_prop_id+0x40/0x40
>   [  632.624909]  drm_ioctl_kernel+0x86/0xd0
>   [  632.624918]  drm_ioctl+0x1e4/0x36b
>   [  632.624925]  ? drm_mode_obj_find_prop_id+0x40/0x40
>   [  632.624939]  do_vfs_ioctl+0x4bd/0x6e0
>   [  632.624949]  ksys_ioctl+0x5e/0x90
>   [  632.624957]  __x64_sys_ioctl+0x16/0x20
>   [  632.624966]  do_syscall_64+0x5a/0x220
>   [  632.624976]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>   [  632.624984] RIP: 0033:0x7f6d2b0de387
>   [  632.624991] Code: 00 00 90 48 8b 05 f9 9a 0c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d c9 9a 0c 00 f7 d8 64 89 01 48
>   [  632.625011] RSP: 002b:00007fffb49def38 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>   [  632.625021] RAX: ffffffffffffffda RBX: 00007fffb49def70 RCX: 00007f6d2b0de387
>   [  632.625030] RDX: 00007fffb49def70 RSI: 00000000c01864ba RDI: 0000000000000009
>   [  632.625040] RBP: 00000000c01864ba R08: 0000000000000000 R09: 00000000c0c0c0c0
>   [  632.625049] R10: 0000000000000030 R11: 0000000000000246 R12: 000055bc367eb920
>   [  632.625058] R13: 0000000000000009 R14: 0000000000000002 R15: 0000000000000000
>   [  632.625071] Modules linked in: ebtable_filter(E) ebtables(E) ip6table_filter(E) ip6_tables(E) iptable_filter(E) ip_tables(E) x_tables(E) af_packet(E) scsi_transport_iscsi(E) dmi_sysfs(E) msr(E) xfs(E) intel_powerclamp(E) coretemp(E) k)
>   [  632.625185] CR2: 0000000000000048
> 
> The STR is
> 
>   * start gdm and wait for it to switch off the display
>   * wake up the display by pressing a key
> 
> The fix implements atomic_check for planes and rejects configurations
> with an invisible primary plane.
> 
> v2:
> 	* do an atomic check for plane
> 	* reject invisible primary planes
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Fixes: b48e1b6ffd28 ("drm/ast: Add CRTC helpers for atomic modesetting")
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: "Y.C. Chen" <yc_chen at aspeedtech.com>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> ---
>  drivers/gpu/drm/ast/ast_mode.c | 50 +++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 4725ec911a66..8e7bb8ce8130 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -31,6 +31,7 @@
>  #include <linux/export.h>
>  #include <linux/pci.h>
> 
> +#include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_atomic_state_helper.h>
>  #include <drm/drm_crtc.h>
> @@ -556,6 +557,31 @@ static const uint32_t ast_primary_plane_formats[] = {
>  int ast_primary_plane_helper_atomic_check(struct drm_plane *plane,
>  					  struct drm_plane_state *state)
>  {
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *crtc_state;
> +	int ret;
> +
> +	if (state->crtc)
> +		crtc = state->crtc;
> +	else if (plane->state && plane->state->crtc)
> +		crtc = plane->state->crtc;
> +	else
> +		return 0; /* disabling an already disabled plane */
> +
> +	crtc_state = drm_atomic_get_new_crtc_state(state->state, crtc);
> +	if (WARN_ON_ONCE(!crtc_state))
> +		return -EINVAL; /* BUG: no new CRTC state allocated */

The above is a lot more complicated than necessary, see e.g.
atmel_hlcdc_plane_atomic_check. And even that is too complicated, since
crtc is set iff fb is set, you only need to check one of them.

> +
> +	ret = drm_atomic_helper_check_plane_state(state, crtc_state,
> +						  DRM_PLANE_HELPER_NO_SCALING,
> +						  DRM_PLANE_HELPER_NO_SCALING,
> +						  false, true);
> +	if (ret)
> +		return ret;
> +
> +	if (!state->visible)
> +		return -EINVAL; /* primary plane must be visible */
> +
>  	return 0;
>  }
> 
> @@ -567,7 +593,7 @@ void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
>  	struct drm_gem_vram_object *gbo;
>  	s64 gpu_addr;
> 
> -	if (!crtc || !state->fb)
> +	if (!crtc || !state->fb || !state->visible)
>  		return;
> 
>  	gbo = drm_gem_vram_of_gem(state->fb->obj[0]);
> @@ -660,6 +686,28 @@ ast_cursor_plane_helper_prepare_fb(struct drm_plane *plane,
>  static int ast_cursor_plane_helper_atomic_check(struct drm_plane *plane,
>  						struct drm_plane_state *state)
>  {
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *crtc_state;
> +	int ret;
> +
> +	if (state->crtc)
> +		crtc = state->crtc;
> +	else if (plane->state && plane->state->crtc)
> +		crtc = plane->state->crtc;
> +	else
> +		return 0; /* disabling an already disabled plane */
> +
> +	crtc_state = drm_atomic_get_new_crtc_state(state->state, crtc);
> +	if (WARN_ON_ONCE(!crtc_state))
> +		return -EINVAL; /* BUG: no new CRTC state allocated */
> +
> +	ret = drm_atomic_helper_check_plane_state(state, crtc_state,
> +						  DRM_PLANE_HELPER_NO_SCALING,
> +						  DRM_PLANE_HELPER_NO_SCALING,
> +						  false, true);

Pretty sure you want your cursor to be positionable ...
-Daniel

> +	if (ret)
> +		return ret;
> +
>  	return 0;
>  }
> 
> --
> 2.23.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

More information about the dri-devel mailing list