drm/i915/bios: Validate fp_timing terminator presence

Validate the LFP data block a bit hardwer by making sure the
fp_timing terminators (0xffff) are where we expect them to be.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220818192223.29881-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_bios.c

@@ -135,18 +135,6 @@ static u32 raw_block_offset(const void *bdb, enum bdb_block_id section_id)
 	return block - bdb;
 }
 
-/* size of the block excluding the header */
-static u32 raw_block_size(const void *bdb, enum bdb_block_id section_id)
-{
-	const void *block;
-
-	block = find_raw_section(bdb, section_id);
-	if (!block)
-		return 0;
-
-	return get_blocksize(block);
-}
-
 struct bdb_block_entry {
 	struct list_head node;
 	enum bdb_block_id section_id;
@@ -231,9 +219,14 @@ static bool validate_lfp_data_ptrs(const void *bdb,
 {
 	int fp_timing_size, dvo_timing_size, panel_pnp_id_size, panel_name_size;
 	int data_block_size, lfp_data_size;
+	const void *data_block;
 	int i;
 
-	data_block_size = raw_block_size(bdb, BDB_LVDS_LFP_DATA);
+	data_block = find_raw_section(bdb, BDB_LVDS_LFP_DATA);
+	if (!data_block)
+		return false;
+
+	data_block_size = get_blocksize(data_block);
 	if (data_block_size == 0)
 		return false;
 
@@ -261,21 +254,6 @@ static bool validate_lfp_data_ptrs(const void *bdb,
 	if (16 * lfp_data_size > data_block_size)
 		return false;
 
-	/*
-	 * Except for vlv/chv machines all real VBTs seem to have 6
-	 * unaccounted bytes in the fp_timing table. And it doesn't
-	 * appear to be a really intentional hole as the fp_timing
-	 * 0xffff terminator is always within those 6 missing bytes.
-	 */
-	if (fp_timing_size + dvo_timing_size + panel_pnp_id_size != lfp_data_size &&
-	    fp_timing_size + 6 + dvo_timing_size + panel_pnp_id_size != lfp_data_size)
-		return false;
-
-	if (ptrs->ptr[0].fp_timing.offset + fp_timing_size > ptrs->ptr[0].dvo_timing.offset ||
-	    ptrs->ptr[0].dvo_timing.offset + dvo_timing_size != ptrs->ptr[0].panel_pnp_id.offset ||
-	    ptrs->ptr[0].panel_pnp_id.offset + panel_pnp_id_size != lfp_data_size)
-		return false;
-
 	/* make sure the table entries have uniform size */
 	for (i = 1; i < 16; i++) {
 		if (ptrs->ptr[i].fp_timing.table_size != fp_timing_size ||
@@ -289,6 +267,23 @@ static bool validate_lfp_data_ptrs(const void *bdb,
 			return false;
 	}
 
+	/*
+	 * Except for vlv/chv machines all real VBTs seem to have 6
+	 * unaccounted bytes in the fp_timing table. And it doesn't
+	 * appear to be a really intentional hole as the fp_timing
+	 * 0xffff terminator is always within those 6 missing bytes.
+	 */
+	if (fp_timing_size + 6 + dvo_timing_size + panel_pnp_id_size == lfp_data_size)
+		fp_timing_size += 6;
+
+	if (fp_timing_size + dvo_timing_size + panel_pnp_id_size != lfp_data_size)
+		return false;
+
+	if (ptrs->ptr[0].fp_timing.offset + fp_timing_size != ptrs->ptr[0].dvo_timing.offset ||
+	    ptrs->ptr[0].dvo_timing.offset + dvo_timing_size != ptrs->ptr[0].panel_pnp_id.offset ||
+	    ptrs->ptr[0].panel_pnp_id.offset + panel_pnp_id_size != lfp_data_size)
+		return false;
+
 	/* make sure the tables fit inside the data block */
 	for (i = 0; i < 16; i++) {
 		if (ptrs->ptr[i].fp_timing.offset + fp_timing_size > data_block_size ||
@@ -300,6 +295,15 @@ static bool validate_lfp_data_ptrs(const void *bdb,
 	if (ptrs->panel_name.offset + 16 * panel_name_size > data_block_size)
 		return false;
 
+	/* make sure fp_timing terminators are present at expected locations */
+	for (i = 0; i < 16; i++) {
+		const u16 *t = data_block + ptrs->ptr[i].fp_timing.offset +
+			fp_timing_size - 2;
+
+		if (*t != 0xffff)
+			return false;
+	}
+
 	return true;
 }