[bug report] drm/amd/display: Initial DC support for Beige Goby

[Dan Carpenter]

Hello Aurabindo Pillai,

The patch cd6d421e3d1a: "drm/amd/display: Initial DC support for
Beige Goby" from Mar 15, 2021, leads to the following Smatch static
checker warning:

    drivers/gpu/drm/amd/amdgpu/../display/dc/dcn303/dcn303_resource.c:392 dcn303_stream_encoder_create()
    error: buffer overflow 'stream_enc_regs' 2 <= 4

    drivers/gpu/drm/amd/amdgpu/../display/dc/dcn301/dcn301_resource.c:1024
    dcn301_stream_encoder_create() error: buffer overflow 'stream_enc_regs' 4 <= 5

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn303/dcn303_resource.c
    366 static struct stream_encoder *dcn303_stream_encoder_create(enum engine_id eng_id, struct dc_context *ctx)
    367 {
    368         struct dcn10_stream_encoder *enc1;
    369         struct vpg *vpg;
    370         struct afmt *afmt;
    371         int vpg_inst;
    372         int afmt_inst;
    373 
    374         /* Mapping of VPG, AFMT, DME register blocks to DIO block instance */
    375         if (eng_id <= ENGINE_ID_DIGE) {
                    ^^^^^^^^^^^^^^^^^^^^^^^^
This tells us that eng_id can be <= 4.


    376                 vpg_inst = eng_id;
    377                 afmt_inst = eng_id;
    378         } else
    379                 return NULL;
    380 
    381         enc1 = kzalloc(sizeof(struct dcn10_stream_encoder), GFP_KERNEL);
    382         vpg = dcn303_vpg_create(ctx, vpg_inst);
    383         afmt = dcn303_afmt_create(ctx, afmt_inst);
    384 
    385         if (!enc1 || !vpg || !afmt) {
    386                 kfree(enc1);
    387                 kfree(vpg);
    388                 kfree(afmt);
    389                 return NULL;
    390         }
    391 
--> 392         dcn30_dio_stream_encoder_construct(enc1, ctx, ctx->dc_bios, eng_id, vpg, afmt, &stream_enc_regs[eng_id],
                                                                                                ^^^^^^^^^^^^^^^
But anything more than 1 is out of bounds.  The dcn301 code is basically
the same.

    393                         &se_shift, &se_mask);
    394 
    395         return &enc1->base;
    396 }

regards,
dan carpenter