[PATCH] drm: nv04: Add check to avoid out of bounds access

[PATCH] drm: nv04: Add check to avoid out of bounds access

[Mikhail Kobuk]

Output Resource (dcb->or) value is not guaranteed to be non-zero (i.e.
in drivers/gpu/drm/nouveau/nouveau_bios.c, in 'fabricate_dcb_encoder_table()'
'dcb->or' is assigned value '0' in call to 'fabricate_dcb_output()').

Add check to validate 'dcb->or' before it's used.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for iMac G4")
Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
---
 drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c b/drivers/gpu/drm/nouveau/dispnv04/dac.c
index d6b8e0cce2ac..0c8d4fc95ff3 100644
--- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
+++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
@@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder *encoder, bool enable)
 	struct drm_device *dev = encoder->dev;
 	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
 
-	if (nv_gf4_disp_arch(dev)) {
+	if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
 		uint32_t *dac_users = &nv04_display(dev)->dac_users[ffs(dcb->or) - 1];
 		int dacclk_off = NV_PRAMDAC_DACCLK + nv04_dac_output_offset(encoder);
 		uint32_t dacclk = NVReadRAMDAC(dev, 0, dacclk_off);
@@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder *encoder)
 	struct drm_device *dev = encoder->dev;
 	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
 
-	return nv_gf4_disp_arch(encoder->dev) &&
+	return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
 		(nv04_display(dev)->dac_users[ffs(dcb->or) - 1] & ~(1 << dcb->index));
 }
 
-- 
2.44.0

Re: [PATCH] drm: nv04: Add check to avoid out of bounds access

[Danilo Krummrich]

On 3/31/24 08:45, Mikhail Kobuk wrote:
> Output Resource (dcb->or) value is not guaranteed to be non-zero (i.e.
> in drivers/gpu/drm/nouveau/nouveau_bios.c, in 'fabricate_dcb_encoder_table()'
> 'dcb->or' is assigned value '0' in call to 'fabricate_dcb_output()').

I don't really know much about the semantics of this code.

Looking at fabricate_dcb_output() though I wonder if the intention was to assign
BIT(or) to entry->or.

@Lyude, can you help here?

Otherwise, for parsing the DCB entries, it seems that the bound checks are
happening in olddcb_outp_foreach() [1].

[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_bios.c#L1331

> 
> Add check to validate 'dcb->or' before it's used.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for iMac G4")
> Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
> ---
>   drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c b/drivers/gpu/drm/nouveau/dispnv04/dac.c
> index d6b8e0cce2ac..0c8d4fc95ff3 100644
> --- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
> +++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
> @@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder *encoder, bool enable)
>   	struct drm_device *dev = encoder->dev;
>   	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>   
> -	if (nv_gf4_disp_arch(dev)) {
> +	if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
>   		uint32_t *dac_users = &nv04_display(dev)->dac_users[ffs(dcb->or) - 1];
>   		int dacclk_off = NV_PRAMDAC_DACCLK + nv04_dac_output_offset(encoder);
>   		uint32_t dacclk = NVReadRAMDAC(dev, 0, dacclk_off);
> @@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder *encoder)
>   	struct drm_device *dev = encoder->dev;
>   	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>   
> -	return nv_gf4_disp_arch(encoder->dev) &&
> +	return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
>   		(nv04_display(dev)->dac_users[ffs(dcb->or) - 1] & ~(1 << dcb->index));
>   }
>   

Re: [PATCH] drm: nv04: Add check to avoid out of bounds access

[Lyude Paul]

On Fri, 2024-04-05 at 17:53 +0200, Danilo Krummrich wrote:
> On 3/31/24 08:45, Mikhail Kobuk wrote:
> > Output Resource (dcb->or) value is not guaranteed to be non-zero
> > (i.e.
> > in drivers/gpu/drm/nouveau/nouveau_bios.c, in
> > 'fabricate_dcb_encoder_table()'
> > 'dcb->or' is assigned value '0' in call to
> > 'fabricate_dcb_output()').
> 
> I don't really know much about the semantics of this code.
> 
> Looking at fabricate_dcb_output() though I wonder if the intention
> was to assign
> BIT(or) to entry->or.
> 
> @Lyude, can you help here?

This code is definitely a bit before my time as well - but I think
you're completely correct. Especially considering this bit I found in
nouveau_bios.h:

enum nouveau_or {
	DCB_OUTPUT_A = (1 << 0),
	DCB_OUTPUT_B = (1 << 1),
	DCB_OUTPUT_C = (1 << 2)
};


> 
> Otherwise, for parsing the DCB entries, it seems that the bound
> checks are
> happening in olddcb_outp_foreach() [1].
> 
> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_bios.c#L1331
> 
> > 
> > Add check to validate 'dcb->or' before it's used.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for
> > iMac G4")
> > Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
> > ---
> >   drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c
> > b/drivers/gpu/drm/nouveau/dispnv04/dac.c
> > index d6b8e0cce2ac..0c8d4fc95ff3 100644
> > --- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
> > +++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
> > @@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder
> > *encoder, bool enable)
> >   	struct drm_device *dev = encoder->dev;
> >   	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
> >   
> > -	if (nv_gf4_disp_arch(dev)) {
> > +	if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
> >   		uint32_t *dac_users = &nv04_display(dev)-
> > >dac_users[ffs(dcb->or) - 1];
> >   		int dacclk_off = NV_PRAMDAC_DACCLK +
> > nv04_dac_output_offset(encoder);
> >   		uint32_t dacclk = NVReadRAMDAC(dev, 0,
> > dacclk_off);
> > @@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder
> > *encoder)
> >   	struct drm_device *dev = encoder->dev;
> >   	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
> >   
> > -	return nv_gf4_disp_arch(encoder->dev) &&
> > +	return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
> >   		(nv04_display(dev)->dac_users[ffs(dcb->or) - 1] &
> > ~(1 << dcb->index));
> >   }
> >   
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

Re: [PATCH] drm: nv04: Add check to avoid out of bounds access

[Danilo Krummrich]

On 4/5/24 22:05, Lyude Paul wrote:
> On Fri, 2024-04-05 at 17:53 +0200, Danilo Krummrich wrote:
>> On 3/31/24 08:45, Mikhail Kobuk wrote:
>>> Output Resource (dcb->or) value is not guaranteed to be non-zero
>>> (i.e.
>>> in drivers/gpu/drm/nouveau/nouveau_bios.c, in
>>> 'fabricate_dcb_encoder_table()'
>>> 'dcb->or' is assigned value '0' in call to
>>> 'fabricate_dcb_output()').
>>
>> I don't really know much about the semantics of this code.
>>
>> Looking at fabricate_dcb_output() though I wonder if the intention
>> was to assign
>> BIT(or) to entry->or.
>>
>> @Lyude, can you help here?
> 
> This code is definitely a bit before my time as well - but I think
> you're completely correct. Especially considering this bit I found in
> nouveau_bios.h:

Thanks for confirming.

@Mikhail, I think we should rather fix this assignment then.

- Danilo

> 
> enum nouveau_or {
> 	DCB_OUTPUT_A = (1 << 0),
> 	DCB_OUTPUT_B = (1 << 1),
> 	DCB_OUTPUT_C = (1 << 2)
> };
> 
> 
>>
>> Otherwise, for parsing the DCB entries, it seems that the bound
>> checks are
>> happening in olddcb_outp_foreach() [1].
>>
>> [1]
>> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_bios.c#L1331
>>
>>>
>>> Add check to validate 'dcb->or' before it's used.
>>>
>>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>>
>>> Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for
>>> iMac G4")
>>> Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
>>> ---
>>>    drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>> b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>> index d6b8e0cce2ac..0c8d4fc95ff3 100644
>>> --- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>> +++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>> @@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder
>>> *encoder, bool enable)
>>>    	struct drm_device *dev = encoder->dev;
>>>    	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>    
>>> -	if (nv_gf4_disp_arch(dev)) {
>>> +	if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
>>>    		uint32_t *dac_users = &nv04_display(dev)-
>>>> dac_users[ffs(dcb->or) - 1];
>>>    		int dacclk_off = NV_PRAMDAC_DACCLK +
>>> nv04_dac_output_offset(encoder);
>>>    		uint32_t dacclk = NVReadRAMDAC(dev, 0,
>>> dacclk_off);
>>> @@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder
>>> *encoder)
>>>    	struct drm_device *dev = encoder->dev;
>>>    	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>    
>>> -	return nv_gf4_disp_arch(encoder->dev) &&
>>> +	return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
>>>    		(nv04_display(dev)->dac_users[ffs(dcb->or) - 1] &
>>> ~(1 << dcb->index));
>>>    }
>>>    
>>
> 

Re: [PATCH] drm: nv04: Add check to avoid out of bounds access

[Mikhail Kobuk]

On 08/04/2024 16:23, Danilo Krummrich wrote:
> On 4/5/24 22:05, Lyude Paul wrote:
>> On Fri, 2024-04-05 at 17:53 +0200, Danilo Krummrich wrote:
>>> On 3/31/24 08:45, Mikhail Kobuk wrote:
>>>> Output Resource (dcb->or) value is not guaranteed to be non-zero
>>>> (i.e.
>>>> in drivers/gpu/drm/nouveau/nouveau_bios.c, in
>>>> 'fabricate_dcb_encoder_table()'
>>>> 'dcb->or' is assigned value '0' in call to
>>>> 'fabricate_dcb_output()').
>>>
>>> I don't really know much about the semantics of this code.
>>>
>>> Looking at fabricate_dcb_output() though I wonder if the intention
>>> was to assign
>>> BIT(or) to entry->or.
>>>
>>> @Lyude, can you help here?
>> 
>> This code is definitely a bit before my time as well - but I think
>> you're completely correct. Especially considering this bit I found in
>> nouveau_bios.h:
> 
> Thanks for confirming.
> 
> @Mikhail, I think we should rather fix this assignment then.

Thank you all for a thorough look!

> 
> - Danilo
> 
>> 
>> enum nouveau_or {
>> 	DCB_OUTPUT_A = (1 << 0),
>> 	DCB_OUTPUT_B = (1 << 1),
>> 	DCB_OUTPUT_C = (1 << 2)
>> };
>> 
>> 

Considering this code bit, and the fact that fabricate_dcb_output() is 
called in drivers/gpu/drm/nouveau/nouveau_bios.c only, there's option to 
adjust function calls instead of adding BIT(or), i.e.:

fabricate_dcb_output(dcb, DCB_OUTPUT_TMDS, 0, all_heads, DCB_OUTPUT_B);

instead of current:

fabricate_dcb_output(dcb, DCB_OUTPUT_TMDS, 0, all_heads, 1);

and etc.

Should I make a new patch with adjusted calls or stick with BIT(or)?

>>>
>>> Otherwise, for parsing the DCB entries, it seems that the bound
>>> checks are
>>> happening in olddcb_outp_foreach() [1].
>>>
>>> [1]
>>> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_bios.c#L1331
>>>
>>>>
>>>> Add check to validate 'dcb->or' before it's used.
>>>>
>>>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>>>
>>>> Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for
>>>> iMac G4")
>>>> Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
>>>> ---
>>>>    drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>> b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>> index d6b8e0cce2ac..0c8d4fc95ff3 100644
>>>> --- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>> +++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>> @@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder
>>>> *encoder, bool enable)
>>>>    	struct drm_device *dev = encoder->dev;
>>>>    	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>>    
>>>> -	if (nv_gf4_disp_arch(dev)) {
>>>> +	if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
>>>>    		uint32_t *dac_users = &nv04_display(dev)-
>>>>> dac_users[ffs(dcb->or) - 1];
>>>>    		int dacclk_off = NV_PRAMDAC_DACCLK +
>>>> nv04_dac_output_offset(encoder);
>>>>    		uint32_t dacclk = NVReadRAMDAC(dev, 0,
>>>> dacclk_off);
>>>> @@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder
>>>> *encoder)
>>>>    	struct drm_device *dev = encoder->dev;
>>>>    	struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>>    
>>>> -	return nv_gf4_disp_arch(encoder->dev) &&
>>>> +	return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
>>>>    		(nv04_display(dev)->dac_users[ffs(dcb->or) - 1] &
>>>> ~(1 << dcb->index));
>>>>    }
>>>>    
>>>
>> 

Re: [PATCH] drm: nv04: Add check to avoid out of bounds access

[Danilo Krummrich]

On 4/10/24 17:39, Mikhail Kobuk wrote:
> On 08/04/2024 16:23, Danilo Krummrich wrote:
>> On 4/5/24 22:05, Lyude Paul wrote:
>>> On Fri, 2024-04-05 at 17:53 +0200, Danilo Krummrich wrote:
>>>> On 3/31/24 08:45, Mikhail Kobuk wrote:
>>>>> Output Resource (dcb->or) value is not guaranteed to be non-zero
>>>>> (i.e.
>>>>> in drivers/gpu/drm/nouveau/nouveau_bios.c, in
>>>>> 'fabricate_dcb_encoder_table()'
>>>>> 'dcb->or' is assigned value '0' in call to
>>>>> 'fabricate_dcb_output()').
>>>>
>>>> I don't really know much about the semantics of this code.
>>>>
>>>> Looking at fabricate_dcb_output() though I wonder if the intention
>>>> was to assign
>>>> BIT(or) to entry->or.
>>>>
>>>> @Lyude, can you help here?
>>>
>>> This code is definitely a bit before my time as well - but I think
>>> you're completely correct. Especially considering this bit I found in
>>> nouveau_bios.h:
>>
>> Thanks for confirming.
>>
>> @Mikhail, I think we should rather fix this assignment then.
> 
> Thank you all for a thorough look!
> 
>>
>> - Danilo
>>
>>>
>>> enum nouveau_or {
>>>     DCB_OUTPUT_A = (1 << 0),
>>>     DCB_OUTPUT_B = (1 << 1),
>>>     DCB_OUTPUT_C = (1 << 2)
>>> };
>>>
>>>
> 
> Considering this code bit, and the fact that fabricate_dcb_output() is called in drivers/gpu/drm/nouveau/nouveau_bios.c only, there's option to adjust function calls instead of adding BIT(or), i.e.:
> 
> fabricate_dcb_output(dcb, DCB_OUTPUT_TMDS, 0, all_heads, DCB_OUTPUT_B);
> 
> instead of current:
> 
> fabricate_dcb_output(dcb, DCB_OUTPUT_TMDS, 0, all_heads, 1);
> 
> and etc.
> 
> Should I make a new patch with adjusted calls or stick with BIT(or)?

Please send a new patch adjusting the calls using enum nouveau_or, that
seems to be cleaner.

- Danilo

> 
>>>>
>>>> Otherwise, for parsing the DCB entries, it seems that the bound
>>>> checks are
>>>> happening in olddcb_outp_foreach() [1].
>>>>
>>>> [1]
>>>> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_bios.c#L1331
>>>>
>>>>>
>>>>> Add check to validate 'dcb->or' before it's used.
>>>>>
>>>>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>>>>
>>>>> Fixes: 2e5702aff395 ("drm/nouveau: fabricate DCB encoder table for
>>>>> iMac G4")
>>>>> Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
>>>>> ---
>>>>>    drivers/gpu/drm/nouveau/dispnv04/dac.c | 4 ++--
>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>>> b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>>> index d6b8e0cce2ac..0c8d4fc95ff3 100644
>>>>> --- a/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>>> +++ b/drivers/gpu/drm/nouveau/dispnv04/dac.c
>>>>> @@ -428,7 +428,7 @@ void nv04_dac_update_dacclk(struct drm_encoder
>>>>> *encoder, bool enable)
>>>>>        struct drm_device *dev = encoder->dev;
>>>>>        struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>>> -    if (nv_gf4_disp_arch(dev)) {
>>>>> +    if (nv_gf4_disp_arch(dev) && ffs(dcb->or)) {
>>>>>            uint32_t *dac_users = &nv04_display(dev)-
>>>>>> dac_users[ffs(dcb->or) - 1];
>>>>>            int dacclk_off = NV_PRAMDAC_DACCLK +
>>>>> nv04_dac_output_offset(encoder);
>>>>>            uint32_t dacclk = NVReadRAMDAC(dev, 0,
>>>>> dacclk_off);
>>>>> @@ -453,7 +453,7 @@ bool nv04_dac_in_use(struct drm_encoder
>>>>> *encoder)
>>>>>        struct drm_device *dev = encoder->dev;
>>>>>        struct dcb_output *dcb = nouveau_encoder(encoder)->dcb;
>>>>> -    return nv_gf4_disp_arch(encoder->dev) &&
>>>>> +    return nv_gf4_disp_arch(encoder->dev) && ffs(dcb->or) &&
>>>>>            (nv04_display(dev)->dac_users[ffs(dcb->or) - 1] &
>>>>> ~(1 << dcb->index));
>>>>>    }
>>>>
>>>
>