drm/radeon/kms/atom: fix handling of FB scratch indices

FB scratch indices are dword indices, but we were treating
them as byte indices.  As such, we were getting the wrong
FB scratch data for non-0 indices.  Fix the indices and
guard the indexing against indices larger than the scratch
allocation.

Fixes memory corruption on some boards if data was written
past the end of the FB scratch array.
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Reported-by: NDave Airlie <airlied@redhat.com>
Tested-by: NDave Airlie <airlied@redhat.com>
Cc: stable@kernel.org
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/atom.c

@@ -277,7 +277,12 @@ static uint32_t atom_get_src_int(atom_exec_context *ctx, uint8_t attr,
 	case ATOM_ARG_FB:
 		idx = U8(*ptr);
 		(*ptr)++;
-		val = gctx->scratch[((gctx->fb_base + idx) / 4)];
+		if ((gctx->fb_base + (idx * 4)) > gctx->scratch_size_bytes) {
+			DRM_ERROR("ATOM: fb read beyond scratch region: %d vs. %d\n",
+				  gctx->fb_base + (idx * 4), gctx->scratch_size_bytes);
+			val = 0;
+		} else
+			val = gctx->scratch[(gctx->fb_base / 4) + idx];
 		if (print)
 			DEBUG("FB[0x%02X]", idx);
 		break;
@@ -531,7 +536,11 @@ static void atom_put_dst(atom_exec_context *ctx, int arg, uint8_t attr,
 	case ATOM_ARG_FB:
 		idx = U8(*ptr);
 		(*ptr)++;
-		gctx->scratch[((gctx->fb_base + idx) / 4)] = val;
+		if ((gctx->fb_base + (idx * 4)) > gctx->scratch_size_bytes) {
+			DRM_ERROR("ATOM: fb write beyond scratch region: %d vs. %d\n",
+				  gctx->fb_base + (idx * 4), gctx->scratch_size_bytes);
+		} else
+			gctx->scratch[(gctx->fb_base / 4) + idx] = val;
 		DEBUG("FB[0x%02X]", idx);
 		break;
 	case ATOM_ARG_PLL:
@@ -1370,11 +1379,13 @@ int atom_allocate_fb_scratch(struct atom_context *ctx)
 
 		usage_bytes = firmware_usage->asFirmwareVramReserveInfo[0].usFirmwareUseInKb * 1024;
 	}
+	ctx->scratch_size_bytes = 0;
 	if (usage_bytes == 0)
 		usage_bytes = 20 * 1024;
 	/* allocate some scratch memory */
 	ctx->scratch = kzalloc(usage_bytes, GFP_KERNEL);
 	if (!ctx->scratch)
 		return -ENOMEM;
+	ctx->scratch_size_bytes = usage_bytes;
 	return 0;
 }

drivers/gpu/drm/radeon/atom.h

@@ -137,6 +137,7 @@ struct atom_context {
 	int cs_equal, cs_above;
 	int io_mode;
 	uint32_t *scratch;
+	int scratch_size_bytes;
 };
 
 extern int atom_debug;