Add bounds checking asserts to memmap IO driver

The memmap IO driver doesn't perform bounds check when reading, writing,
or seeking. The onus to vet parameters is on the caller, and this patch
asserts that:

  - non-negative size is specified for for backing memory;

  - valid parameters are passed into the driver for read, write and seek
    operations.

Change-Id: I6518c4065817e640e9e7e39a8a4577655f2680f7
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

drivers/io/io_memmap.c

 /*
- * Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2017, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -118,13 +118,14 @@ static int memmap_dev_close(io_dev_info_t *dev_info)
 
 
 /* Open a file on the memmap device */
-/* TODO: Can we do any sensible limit checks on requested memory */
 static int memmap_block_open(io_dev_info_t *dev_info, const uintptr_t spec,
 			     io_entity_t *entity)
 {
 	int result = -ENOMEM;
 	const io_block_spec_t *block_spec = (io_block_spec_t *)spec;
 
+	assert(block_spec->length >= 0);
+
 	/* Since we need to track open state for seek() we only allow one open
 	 * spec at a time. When we have dynamic memory we can malloc and set
 	 * entity->info.
@@ -152,13 +153,19 @@ static int memmap_block_open(io_dev_info_t *dev_info, const uintptr_t spec,
 static int memmap_block_seek(io_entity_t *entity, int mode, ssize_t offset)
 {
 	int result = -ENOENT;
+	file_state_t *fp;
 
 	/* We only support IO_SEEK_SET for the moment. */
 	if (mode == IO_SEEK_SET) {
 		assert(entity != NULL);
 
-		/* TODO: can we do some basic limit checks on seek? */
-		((file_state_t *)entity->info)->file_pos = offset;
+		fp = (file_state_t *) entity->info;
+
+		/* Assert that new file position is valid */
+		assert((offset >= 0) && (offset < fp->size));
+
+		/* Reset file position */
+		fp->file_pos = offset;
 		result = 0;
 	}
 
@@ -183,18 +190,24 @@ static int memmap_block_read(io_entity_t *entity, uintptr_t buffer,
 			     size_t length, size_t *length_read)
 {
 	file_state_t *fp;
+	size_t pos_after;
 
 	assert(entity != NULL);
 	assert(buffer != (uintptr_t)NULL);
 	assert(length_read != NULL);
 
-	fp = (file_state_t *)entity->info;
+	fp = (file_state_t *) entity->info;
+
+	/* Assert that file position is valid for this read operation */
+	pos_after = fp->file_pos + length;
+	assert((pos_after >= fp->file_pos) && (pos_after <= fp->size));
 
 	memcpy((void *)buffer, (void *)(fp->base + fp->file_pos), length);
 
 	*length_read = length;
-	/* advance the file 'cursor' for incremental reads */
-	fp->file_pos += length;
+
+	/* Set file position after read */
+	fp->file_pos = pos_after;
 
 	return 0;
 }
@@ -205,19 +218,24 @@ static int memmap_block_write(io_entity_t *entity, const uintptr_t buffer,
 			      size_t length, size_t *length_written)
 {
 	file_state_t *fp;
+	size_t pos_after;
 
 	assert(entity != NULL);
 	assert(buffer != (uintptr_t)NULL);
 	assert(length_written != NULL);
 
-	fp = (file_state_t *)entity->info;
+	fp = (file_state_t *) entity->info;
+
+	/* Assert that file position is valid for this write operation */
+	pos_after = fp->file_pos + length;
+	assert((pos_after >= fp->file_pos) && (pos_after <= fp->size));
 
 	memcpy((void *)(fp->base + fp->file_pos), (void *)buffer, length);
 
 	*length_written = length;
 
-	/* advance the file 'cursor' for incremental writes */
-	fp->file_pos += length;
+	/* Set file position after write */
+	fp->file_pos = pos_after;
 
 	return 0;
 }