drm/i915/bios: Validate LFP data table pointers

Make sure the LFP data table pointers sane. Sensible looking
table entries, everything points correctly into the data block,
etc.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405173410.11436-5-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -133,6 +133,18 @@ static u32 block_offset(const void *bdb, enum bdb_block_id section_id)
 	return block - bdb;
 }
 
+/* size of the block excluding the header */
+static u32 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;
@@ -191,6 +203,74 @@ static const struct {
 	  .min_size = sizeof(struct bdb_generic_dtd), },
 };
 
+static bool validate_lfp_data_ptrs(const void *bdb,
+				   const struct bdb_lvds_lfp_data_ptrs *ptrs)
+{
+	int fp_timing_size, dvo_timing_size, panel_pnp_id_size;
+	int data_block_size, lfp_data_size;
+	int i;
+
+	data_block_size = block_size(bdb, BDB_LVDS_LFP_DATA);
+	if (data_block_size == 0)
+		return false;
+
+	/* always 3 indicating the presence of fp_timing+dvo_timing+panel_pnp_id */
+	if (ptrs->lvds_entries != 3)
+		return false;
+
+	fp_timing_size = ptrs->ptr[0].fp_timing.table_size;
+	dvo_timing_size = ptrs->ptr[0].dvo_timing.table_size;
+	panel_pnp_id_size = ptrs->ptr[0].panel_pnp_id.table_size;
+
+	/* fp_timing has variable size */
+	if (fp_timing_size < 32 ||
+	    dvo_timing_size != sizeof(struct lvds_dvo_timing) ||
+	    panel_pnp_id_size != sizeof(struct lvds_pnp_id))
+		return false;
+
+	lfp_data_size = ptrs->ptr[1].fp_timing.offset - ptrs->ptr[0].fp_timing.offset;
+	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 ||
+		    ptrs->ptr[i].dvo_timing.table_size != dvo_timing_size ||
+		    ptrs->ptr[i].panel_pnp_id.table_size != panel_pnp_id_size)
+			return false;
+
+		if (ptrs->ptr[i].fp_timing.offset - ptrs->ptr[i-1].fp_timing.offset != lfp_data_size ||
+		    ptrs->ptr[i].dvo_timing.offset - ptrs->ptr[i-1].dvo_timing.offset != lfp_data_size ||
+		    ptrs->ptr[i].panel_pnp_id.offset - ptrs->ptr[i-1].panel_pnp_id.offset != 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 ||
+		    ptrs->ptr[i].dvo_timing.offset + dvo_timing_size > data_block_size ||
+		    ptrs->ptr[i].panel_pnp_id.offset + panel_pnp_id_size > data_block_size)
+			return false;
+	}
+
+	return true;
+}
+
 /* make the data table offsets relative to the data block */
 static bool fixup_lfp_data_ptrs(const void *bdb, void *ptrs_block)
 {
@@ -211,7 +291,7 @@ static bool fixup_lfp_data_ptrs(const void *bdb, void *ptrs_block)
 		ptrs->ptr[i].panel_pnp_id.offset -= offset;
 	}
 
-	return true;
+	return validate_lfp_data_ptrs(bdb, ptrs);
 }
 
 static void