2023-08-21 11:09:48

by Su Hui

Subject: [PATCH v2] drm/amdgpu: Avoid possible buffer overflow

smatch error:
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257 amdgpu_discovery_reg_base_init() error:
testing array offset 'adev->vcn.num_vcn_inst' after use.

change the assignment order to avoid buffer overflow.

Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
Signed-off-by: Su Hui <[email protected]>
---
changes in v2:
- fix the error about ip->revision (thanks to Christophe JAILLET).
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index 8e1cfc87122d..b07bfd106a9b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1250,11 +1250,10 @@ static int amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
* 0b10 : encode is disabled
* 0b01 : decode is disabled
*/
- adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
- ip->revision & 0xc0;
- ip->revision &= ~0xc0;
if (adev->vcn.num_vcn_inst <
AMDGPU_MAX_VCN_INSTANCES) {
+ adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
+ ip->revision & 0xc0;
adev->vcn.num_vcn_inst++;
adev->vcn.inst_mask |=
(1U << ip->instance_number);
@@ -1265,6 +1264,7 @@ static int amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
adev->vcn.num_vcn_inst + 1,
AMDGPU_MAX_VCN_INSTANCES);
}
+ ip->revision &= ~0xc0;
}
if (le16_to_cpu(ip->hw_id) == SDMA0_HWID ||
le16_to_cpu(ip->hw_id) == SDMA1_HWID ||
--
2.30.2

2023-08-22 08:01:51

by Su Hui

Subject: Re: [PATCH v2] drm/amdgpu: Avoid possible buffer overflow

On 2023/8/21 17:31, Christian König wrote:
> Am 21.08.23 um 09:37 schrieb Su Hui:
>> smatch error:
>> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257
>> amdgpu_discovery_reg_base_init() error:
>> testing array offset 'adev->vcn.num_vcn_inst' after use.
>>
>> change the assignment order to avoid buffer overflow.
>>
>> Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
>> Signed-off-by: Su Hui <[email protected]>
>> ---
>> changes in v2:
>>   - fix the error about ip->revision (thanks to Christophe JAILLET).
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
>> index 8e1cfc87122d..b07bfd106a9b 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
>> @@ -1250,11 +1250,10 @@ static int
>> amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
>>                    *     0b10 : encode is disabled
>>                    *     0b01 : decode is disabled
>>                    */
>> - adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
>> -                    ip->revision & 0xc0;
>> -                ip->revision &= ~0xc0;
>>                   if (adev->vcn.num_vcn_inst <
>>                       AMDGPU_MAX_VCN_INSTANCES) {
>> + adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
>> +                        ip->revision & 0xc0;
>>                       adev->vcn.num_vcn_inst++;
>>                       adev->vcn.inst_mask |=
>>                           (1U << ip->instance_number);
>> @@ -1265,6 +1264,7 @@ static int
>> amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
>>                           adev->vcn.num_vcn_inst + 1,
>>                           AMDGPU_MAX_VCN_INSTANCES);
>>                   }
>> +                ip->revision &= ~0xc0;
>
> That doesn't looks correct either. The assignment is intentionally
> outside of the "if".
>
> See "adev->vcn.vcn_config[adev->vcn.num_vcn_inst] = ip->revision &
> 0xc0;" is always valid.

Hi,

if "adev->vcn.vcn_config[adev->vcn.num_vcn_inst] = ip->revision & 0xc0;"
is always valid, then

"adev->vcn.num_vcn_inst< AMDGPU_MAX_VCN_INSTANCES " is always true. So
the below judgement has

no sense.

                  if (adev->vcn.num_vcn_inst <
                      AMDGPU_MAX_VCN_INSTANCES) {

On the contrary, if we need this judgement, then
"adev->vcn.vcn_config[adev->vcn.num_vcn_inst] = ip->revision & 0xc0;"is not

always valid, because "adev->vcn.num_vcn_inst >=
AMDGPU_MAX_VCN_INSTANCES" can be true, which cause buffer overflow.

So I think this patch has some sense if I don't make some mistakes.

Su Hui

>
> We just avoid incrementing num_vcn_inst when we already have to many.
>
> Regards,
> Christian.
>
>
>>               }
>>               if (le16_to_cpu(ip->hw_id) == SDMA0_HWID ||
>>                   le16_to_cpu(ip->hw_id) == SDMA1_HWID ||
>