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

[Daniel Vetter]

On Wed, Oct 9, 2019 at 8:23 PM Lakha, Bhawanpreet
<Bhawanpreet.Lakha at amd.com> wrote:
>
> Hi,
>
> The reason we don't use drm_hdcp is because our policy is to do hdcp
> verification using PSP/HW (onboard secure processor).

i915 also uses hw to auth, we still use the parts from drm_hdcp ...
Did you actually look at what's in there? It's essentially just shared
defines and data structures from the standard, plus a few minimal
helpers to en/decode some bits. Just from a quick read the entire
patch very much looks like midlayer everywhere design that we
discussed back when DC landed ...
-Daniel

>
> 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
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch