thunderbolt: dma_port: Fix NVM read buffer bounds and offset issue

Up to 64 bytes of data can be read from NVM in one go. Read address
must be dword aligned. Data is read into a local buffer.

If caller asks to read data starting at an unaligned address then full
dword is anyway read from NVM into a local buffer. Data is then copied
from the local buffer starting at the unaligned offset to the caller
buffer.

In cases where asked data length + unaligned offset is over 64 bytes
we need to make sure we don't read past the 64 bytes in the local
buffer when copying to caller buffer, and make sure that we don't
skip copying unaligned offset bytes from local buffer anymore after
the first round of 64 byte NVM data read.

Fixes: 3e136768 ("thunderbolt: Add support for DMA configuration based mailbox")
Cc: stable@vger.kernel.org
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/dma_port.c

@@ -366,15 +366,15 @@ int dma_port_flash_read(struct tb_dma_port *dma, unsigned int address,
 			void *buf, size_t size)
 {
 	unsigned int retries = DMA_PORT_RETRIES;
-	unsigned int offset;
-
-	offset = address & 3;
-	address = address & ~3;
 
 	do {
-		u32 nbytes = min_t(u32, size, MAIL_DATA_DWORDS * 4);
+		unsigned int offset;
+		size_t nbytes;
 		int ret;
 
+		offset = address & 3;
+		nbytes = min_t(size_t, size + offset, MAIL_DATA_DWORDS * 4);
+
 		ret = dma_port_flash_read_block(dma, address, dma->buf,
 						ALIGN(nbytes, 4));
 		if (ret) {
@@ -386,6 +386,7 @@ int dma_port_flash_read(struct tb_dma_port *dma, unsigned int address,
 			return ret;
 		}
 
+		nbytes -= offset;
 		memcpy(buf, dma->buf + offset, nbytes);
 
 		size -= nbytes;