Re: [PATCH v4 4/4] media: venus: hfi: add a check to handle OOB in sfr region

[Vikash Garodia <quic_vgarodia@quicinc.com>]

On 2/21/2025 9:25 AM, Tomasz Figa wrote:
> On Fri, Feb 21, 2025 at 12:56 AM Vikash Garodia
> <quic_vgarodia@quicinc.com> wrote:
>>
>>
>> On 2/20/2025 8:53 PM, Hans Verkuil wrote:
>>> On 2/7/25 09:24, Vikash Garodia wrote:
>>>> sfr->buf_size is in shared memory and can be modified by malicious user.
>>>> OOB write is possible when the size is made higher than actual sfr data
>>>> buffer. Cap the size to allocated size for such cases.
>>>>
>>>> Cc: stable@vger.kernel.org
>>>> Fixes: d96d3f30c0f2 ("[media] media: venus: hfi: add Venus HFI files")
>>>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
>>>> Signed-off-by: Vikash Garodia <quic_vgarodia@quicinc.com>
>>>> ---
>>>>  drivers/media/platform/qcom/venus/hfi_venus.c | 9 +++++++--
>>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/media/platform/qcom/venus/hfi_venus.c b/drivers/media/platform/qcom/venus/hfi_venus.c
>>>> index 6b615270c5dae470c6fad408c9b5bc037883e56e..c3113420d266e61fcab44688580288d7408b50f4 100644
>>>> --- a/drivers/media/platform/qcom/venus/hfi_venus.c
>>>> +++ b/drivers/media/platform/qcom/venus/hfi_venus.c
>>>> @@ -1041,18 +1041,23 @@ static void venus_sfr_print(struct venus_hfi_device *hdev)
>>>>  {
>>>>      struct device *dev = hdev->core->dev;
>>>>      struct hfi_sfr *sfr = hdev->sfr.kva;
>>>> +    u32 size;
>>>>      void *p;
>>>>
>>>>      if (!sfr)
>>>>              return;
>>>>
>>>> -    p = memchr(sfr->data, '\0', sfr->buf_size);
>>>> +    size = sfr->buf_size;
>>>
>>> If this is ever 0...
>>>
>>>> +    if (size > ALIGNED_SFR_SIZE)
>>>> +            size = ALIGNED_SFR_SIZE;
>>>> +
>>>> +    p = memchr(sfr->data, '\0', size);
>>>>      /*
>>>>       * SFR isn't guaranteed to be NULL terminated since SYS_ERROR indicates
>>>>       * that Venus is in the process of crashing.
>>>>       */
>>>>      if (!p)
>>>> -            sfr->data[sfr->buf_size - 1] = '\0';
>>>> +            sfr->data[size - 1] = '\0';
>>>
>>> ...then this will overwrite memory. It probably can't be 0, but a check or perhaps
>>> just a comment might be good. It looks a bit scary.
>> Thats correct, it would not be 0 as its a prefixed one [1]. I can put up a
>> comment here.
> 
> Couldn't a bug (or vulnerability) in the firmware actually still cause
> it to write 0 there?
Possible. Though the size is initialized in driver with "ALIGNED_SFR_SIZE",
there is a possibility that the same could get overwritten by a rogue firmware.
Kept a check in v5, which cache the value locally and then does the check before
using that value.

Regards
Vikash
>>
>> [1]
>> https://elixir.bootlin.com/linux/v6.14-rc3/source/drivers/media/platform/qcom/venus/hfi_venus.c#L836
>>>
>>> Regards,
>>>
>>>       Hans
>>>
>>>>
>>>>      dev_err_ratelimited(dev, "SFR message from FW: %s\n", sfr->data);
>>>>  }
>>>>
>> Regards,
>> Vikash