Re: [PATCH] drm/amdgpu: zero reg_state buffer before filling it

[Christian König]

On 9/14/26 16:45, Lazar, Lijo wrote:
> 
> 
> On 14-Sep-26 7:30 PM, Christian König wrote:
>> On 9/14/26 15:56, Dmitriy Chumachenko wrote:
>>> The reg_state readouts return szbuf bytes but never write the pad members
>>> of the headers and of amdgpu_smn_reg_data (and, for pcie, the fields
>>> skipped when the upstream port or AER capability is absent). The sysfs
>>> buffer is a plain kmalloc(), so those bytes leak stale slab data to any
>>> local user through the 0444 reg_state attribute.
>>>
>>> Zero the buffer once the size is known.
>>>
>>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>>
>>> Fixes: 081a6eda2b25 ("drm/amdgpu: Read aquavanjaram PCIE register state")
>>> Signed-off-by: Dmitriy Chumachenko <Dmitry.Chumachenko@xxxxxxxxxxxxxxx>
>>
>> Good catch, but stuff like that should be handled by using kzalloc() instead of calling memset it manually.
>>
> 
> It's the default sysfs buffer allocation which may not be used entirely by all drivers.
> 
> The concern in this case is that driver is telling it has written x bytes whereas it could have left some fields unfilled in the buffer. I think the fix is fine.

Wait a second, is that because of messed up padding in sysfs structures? That is usually a really big NO-GO for upstreaming.

Structures returned to userspace must be padding free, see the tool pahole for how to double check that on different architectures.

Regards,
Christian.

> 
> Thanks,
> Lijo
> 
>> Regards,
>> Christian.
>>
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/aqua_vanjaram.c | 8 ++++++++
>>>   1 file changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/aqua_vanjaram.c b/drivers/gpu/drm/amd/amdgpu/aqua_vanjaram.c
>>> index 72ea37dbfea8..0086de0f685d 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/aqua_vanjaram.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/aqua_vanjaram.c
>>> @@ -610,6 +610,8 @@ static ssize_t aqua_vanjaram_read_pcie_state(struct amdgpu_device *adev,
>>>          if (max_size < szbuf)
>>>                  return -EOVERFLOW;
>>>
>>> +       memset(buf, 0, szbuf);
>>> +
>>>          pcie_regs = (struct amdgpu_regs_pcie_v1_0 *)((uint8_t *)buf +
>>>                                                       sizeof(*pcie_reg_state));
>>>          pcie_regs->inst_header.instance = 0;
>>> @@ -702,6 +704,8 @@ static ssize_t aqua_vanjaram_read_xgmi_state(struct amdgpu_device *adev,
>>>          if (max_size < szbuf)
>>>                  return -EOVERFLOW;
>>>
>>> +       memset(buf, 0, szbuf);
>>> +
>>>          p = &xgmi_reg_state->xgmi_state_regs[0];
>>>          for_each_inst(i, adev->aid_mask) {
>>>                  for (j = 0; j < xgmi_inst; ++j) {
>>> @@ -776,6 +780,8 @@ static ssize_t aqua_vanjaram_read_wafl_state(struct amdgpu_device *adev,
>>>          if (max_size < szbuf)
>>>                  return -EOVERFLOW;
>>>
>>> +       memset(buf, 0, szbuf);
>>> +
>>>          p = &wafl_reg_state->wafl_state_regs[0];
>>>          for_each_inst(i, adev->aid_mask) {
>>>                  for (j = 0; j < wafl_inst; ++j) {
>>> @@ -902,6 +908,8 @@ static ssize_t aqua_vanjaram_read_usr_state(struct amdgpu_device *adev,
>>>          if (max_size < szbuf)
>>>                  return -EOVERFLOW;
>>>
>>> +       memset(buf, 0, szbuf);
>>> +
>>>          p = &usr_reg_state->usr_state_regs[0];
>>>          for_each_inst(i, adev->aid_mask) {
>>>                  usr_regs = (struct amdgpu_regs_usr_v1_0 *)p;
>>> -- 
>>> 2.49.0
>>>
>>
>