On 13/11/2020 14:55, Sam Ravnborg wrote:
> Hi Colin.
>
> On Fri, Nov 13, 2020 at 12:01:21PM +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>
>> Writes to elements in the kmb->plane_status array in function
>> kmb_plane_atomic_disable are overrunning the array when plane_id is
>> more than 1 because currently the array is KMB_MAX_PLANES elements
>> in size and this is currently #defined as 1. Fix this by defining
>> KMB_MAX_PLANES to 4.
>
> I fail to follow you here.
> In kmb_plane_init() only one plane is allocated - with id set to 0.
> So for now only one plane is allocated thus kmb_plane_atomic_disable()
> is only called for this plane.
>
> With your change we will start allocating four planes, something that is
> not tested.
>
> Do I miss something?
>
> Sam
>
The static analysis from coverity on linux-next suggested that there was
an array overflow as follows:
108 static void kmb_plane_atomic_disable(struct drm_plane *plane,
109 struct drm_plane_state *state)
110 {
1. Condition 0 /* !!(!__builtin_types_compatible_p() &&
!__builtin_types_compatible_p()) */, taking false branch.
111 struct kmb_plane *kmb_plane = to_kmb_plane(plane);
2. assignment: Assigning: plane_id = kmb_plane->id.
112 int plane_id = kmb_plane->id;
113 struct kmb_drm_private *kmb;
114
115 kmb = to_kmb(plane->dev);
116
3. Switch case value LAYER_3.
117 switch (plane_id) {
118 case LAYER_0:
119 kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
120 break;
121 case LAYER_1:
(#2 of 4): Out-of-bounds write (OVERRUN)
122 kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL2_ENABLE;
123 break;
124 case LAYER_2:
(#3 of 4): Out-of-bounds write (OVERRUN)
125 kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL1_ENABLE;
126 break;
4. equality_cond: Jumping to case LAYER_3.
127 case LAYER_3:
(#1 of 4): Out-of-bounds write (OVERRUN)
5. overrun-local: Overrunning array kmb->plane_status of 1 8-byte
elements at element index 3 (byte offset 31) using index plane_id (which
evaluates to 3).
128 kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL2_ENABLE;
129 break;
130 }
131
(#4 of 4): Out-of-bounds write (OVERRUN)
132 kmb->plane_status[plane_id].disable = true;
133 }
134
So it seems the assignments to kmb->plane_status[plane_id] are
overrunning the array since plane_status is allocated as 1 element and
yet plane_id can be 0..3
I could be misunderstanding this, or it may be a false positive.
Colin
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