[PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

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.

Addresses-Coverity: ("Out-of-bounds write")
Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/gpu/drm/kmb/kmb_plane.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/kmb/kmb_plane.h b/drivers/gpu/drm/kmb/kmb_plane.h
index 486490f7a3ec..6f43a7ae3de6 100644
--- a/drivers/gpu/drm/kmb/kmb_plane.h
+++ b/drivers/gpu/drm/kmb/kmb_plane.h
@@ -43,7 +43,7 @@ enum layer_id {
 	/* KMB_MAX_PLANES */
 };
 
-#define KMB_MAX_PLANES 1
+#define KMB_MAX_PLANES 4
 
 enum sub_plane_id {
 	Y_PLANE,
-- 
2.28.0

Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Sam Ravnborg]

Hi Colin.

On Fri, Nov 13, 2020 at 12:01:21PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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

Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Colin Ian King]

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@canonical.com>
>>
>> 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

Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Sam Ravnborg]

Hi Colin.
On Fri, Nov 13, 2020 at 03:04:34PM +0000, Colin Ian King wrote:
> 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@canonical.com>
> >>
> >> 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;

With the current code this is the only case that hits.
So coverity is right that if we hit other cases that would result in a
bug. But kmb_plane->id will for now not have other values than 0.

So it is a subtle false positive.
There is some "dead" code here - but this is in preparation for more
than one layer and we will keep the code for now, unless Anitha chimes
in and says otherwise.

	Sam

> 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

RE: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Chrisanthus, Anitha]

Hi Sam and Colin,

> -----Original Message-----
> From: Sam Ravnborg <sam@ravnborg.org>
> Sent: Friday, November 13, 2020 10:02 AM
> To: Colin Ian King <colin.king@canonical.com>
> Cc: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>; Dea, Edmund J
> <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
> <daniel@ffwll.ch>; dri-devel@lists.freedesktop.org; kernel-
> janitors@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb-
> >plane_status[]
> 
> Hi Colin.
> On Fri, Nov 13, 2020 at 03:04:34PM +0000, Colin Ian King wrote:
> > 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@canonical.com>
> > >>
> > >> 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;
> 
> With the current code this is the only case that hits.
> So coverity is right that if we hit other cases that would result in a
> bug. But kmb_plane->id will for now not have other values than 0.
> 
> So it is a subtle false positive.
> There is some "dead" code here - but this is in preparation for more
> than one layer and we will keep the code for now, unless Anitha chimes
> in and says otherwise.

Thanks Sam, I was out on Friday. Agree with Sam, let's keep the current code for now. Kmb->plane_id will not have non-zero values now.
Only one plane is supported and tested currently, the extra code is in preparation for multiple planes.

Thanks,
Anitha
> 
> 	Sam
> 
> > 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

Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane_status[]

[Colin Ian King]

On 16/11/2020 16:53, Chrisanthus, Anitha wrote:
> Hi Sam and Colin,
> 
>> -----Original Message-----
>> From: Sam Ravnborg <sam@ravnborg.org>
>> Sent: Friday, November 13, 2020 10:02 AM
>> To: Colin Ian King <colin.king@canonical.com>
>> Cc: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>; Dea, Edmund J
>> <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
>> <daniel@ffwll.ch>; dri-devel@lists.freedesktop.org; kernel-
>> janitors@vger.kernel.org; linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb-
>>> plane_status[]
>>
>> Hi Colin.
>> On Fri, Nov 13, 2020 at 03:04:34PM +0000, Colin Ian King wrote:
>>> 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@canonical.com>
>>>>>
>>>>> 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;
>>
>> With the current code this is the only case that hits.
>> So coverity is right that if we hit other cases that would result in a
>> bug. But kmb_plane->id will for now not have other values than 0.
>>
>> So it is a subtle false positive.
>> There is some "dead" code here - but this is in preparation for more
>> than one layer and we will keep the code for now, unless Anitha chimes
>> in and says otherwise.
> 
> Thanks Sam, I was out on Friday. Agree with Sam, let's keep the current code for now. Kmb->plane_id will not have non-zero values now.
> Only one plane is supported and tested currently, the extra code is in preparation for multiple planes.

Thanks for the clarification. Apologies for the noise.

> 
> Thanks,
> Anitha
>>
>> 	Sam
>>
>>> 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