drm/amd/display: Add HDCP module - static analysis bug report

[Lakha, Bhawanpreet]

Hi,

The reason we don't use drm_hdcp is because our policy is to do hdcp 
verification using PSP/HW (onboard secure processor).

Bhawan

On 2019-10-09 12:32 p.m., Daniel Vetter wrote:
> On Thu, Oct 03, 2019 at 11:08:03PM +0100, Colin Ian King wrote:
>> Hi,
>>
>> Static analysis with Coverity has detected a potential issue with
>> function validate_bksv in
>> drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c with recent
>> commit:
>>
>> commit ed9d8e2bcb003ec94658cafe9b1bb3960e2139ec
>> Author: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>
>> Date:   Tue Aug 6 17:52:01 2019 -0400
>>
>>      drm/amd/display: Add HDCP module
> I think the real question here is ... why is this not using drm_hdcp?
> -Daniel
>
>>
>> The analysis is as follows:
>>
>>   28 static inline enum mod_hdcp_status validate_bksv(struct mod_hdcp *hdcp)
>>   29 {
>>
>> CID 89852 (#1 of 1): Out-of-bounds read (OVERRUN)
>>
>> 1. overrun-local:
>> Overrunning array of 5 bytes at byte offset 7 by dereferencing pointer
>> (uint64_t *)hdcp->auth.msg.hdcp1.bksv.
>>
>>   30        uint64_t n = *(uint64_t *)hdcp->auth.msg.hdcp1.bksv;
>>   31        uint8_t count = 0;
>>   32
>>   33        while (n) {
>>   34                count++;
>>   35                n &= (n - 1);
>>   36        }
>>
>> hdcp->auth.msg.hdcp1.bksv is an array of 5 uint8_t as defined in
>> drivers/gpu/drm/amd/display/modules/hdcp/hdcp.h as follows:
>>
>> struct mod_hdcp_message_hdcp1 {
>>          uint8_t         an[8];
>>          uint8_t         aksv[5];
>>          uint8_t         ainfo;
>>          uint8_t         bksv[5];
>>          uint16_t        r0p;
>>          uint8_t         bcaps;
>>          uint16_t        bstatus;
>>          uint8_t         ksvlist[635];
>>          uint16_t        ksvlist_size;
>>          uint8_t         vp[20];
>>
>>          uint16_t        binfo_dp;
>> };
>>
>> variable n is going to contain the contains of r0p and bcaps. I'm not
>> sure if that is intentional. If not, then the count is going to be
>> incorrect if these are non-zero.
>>
>> Colin