wlcore: make some of the fwlog calculations more obvious

Make some of the fwlog calculations more obvious by calculating bits
that get used and documenting what they are. Validate the read pointer
while we're at it to ensure we do not overflow the data block we have
allocated and read.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/E1lolvX-0003R3-RE@rmk-PC.armlinux.org.uk

drivers/net/wireless/ti/wlcore/event.c

@@ -29,11 +29,13 @@ int wlcore_event_fw_logger(struct wl1271 *wl)
 	u8  *buffer;
 	u32 internal_fw_addrbase = WL18XX_DATA_RAM_BASE_ADDRESS;
 	u32 addr = WL18XX_LOGGER_SDIO_BUFF_ADDR;
-	u32 end_buff_addr = WL18XX_LOGGER_SDIO_BUFF_ADDR +
-				WL18XX_LOGGER_BUFF_OFFSET;
+	u32 addr_ptr;
+	u32 buff_start_ptr;
+	u32 buff_read_ptr;
+	u32 buff_end_ptr;
 	u32 available_len;
 	u32 actual_len;
-	u32 clear_addr;
+	u32 clear_ptr;
 	size_t len;
 	u32 start_loc;
 
@@ -59,17 +61,29 @@ int wlcore_event_fw_logger(struct wl1271 *wl)
 	if (actual_len == 0)
 		goto free_out;
 
-	start_loc = (le32_to_cpu(fw_log.buff_read_ptr) -
-			internal_fw_addrbase) - addr;
-	end_buff_addr += le32_to_cpu(fw_log.max_buff_size);
-	available_len = end_buff_addr -
-			(le32_to_cpu(fw_log.buff_read_ptr) -
-				 internal_fw_addrbase);
+	/* Calculate the internal pointer to the fwlog structure */
+	addr_ptr = internal_fw_addrbase + addr;
 
-	/* Copy initial part from end of ring buffer */
+	/* Calculate the internal pointers to the start and end of log buffer */
+	buff_start_ptr = addr_ptr + WL18XX_LOGGER_BUFF_OFFSET;
+	buff_end_ptr = buff_start_ptr + le32_to_cpu(fw_log.max_buff_size);
+
+	/* Read the read pointer and validate it */
+	buff_read_ptr = le32_to_cpu(fw_log.buff_read_ptr);
+	if (buff_read_ptr < buff_start_ptr ||
+	    buff_read_ptr >= buff_end_ptr) {
+		wl1271_error("buffer read pointer out of bounds: %x not in (%x-%x)\n",
+			     buff_read_ptr, buff_start_ptr, buff_end_ptr);
+		goto free_out;
+	}
+
+	start_loc = buff_read_ptr - addr_ptr;
+	available_len = buff_end_ptr - buff_read_ptr;
+
+	/* Copy initial part up to the end of ring buffer */
 	len = min(actual_len, available_len);
 	wl12xx_copy_fwlog(wl, &buffer[start_loc], len);
-	clear_addr = addr + start_loc + actual_len + internal_fw_addrbase;
+	clear_ptr = addr_ptr + start_loc + actual_len;
 
 	/* Copy any remaining part from beginning of ring buffer */
 	len = actual_len - len;
@@ -77,14 +91,13 @@ int wlcore_event_fw_logger(struct wl1271 *wl)
 		wl12xx_copy_fwlog(wl,
 				  &buffer[WL18XX_LOGGER_BUFF_OFFSET],
 				  len);
-		clear_addr = addr + WL18XX_LOGGER_BUFF_OFFSET + len +
-				internal_fw_addrbase;
+		clear_ptr = addr_ptr + WL18XX_LOGGER_BUFF_OFFSET + len;
 	}
 
 	/* double check that clear address and write pointer are the same */
-	if (clear_addr != le32_to_cpu(fw_log.buff_write_ptr)) {
+	if (clear_ptr != le32_to_cpu(fw_log.buff_write_ptr)) {
 		wl1271_error("Calculate of clear addr Clear = %x, write = %x",
-			     clear_addr, le32_to_cpu(fw_log.buff_write_ptr));
+			     clear_ptr, le32_to_cpu(fw_log.buff_write_ptr));
 	}
 
 	/* indicate FW about Clear buffer */