spi: mediatek: Prevent overflows in FIFO transfers

In the case where transfer length is not a multiple of 4, KASAN
reports 2 out-of-bounds memory accesses:
 - mtk_spi_interrupt: ioread32_rep writes past the end of
   trans->rx_buf.
 - mtk_spi_fifo_transfer: iowrite32_rep reads past the end of
   xfer->tx_buf.

Fix this by using memcpy on the remainder of the bytes.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
index 563954a61424..375d412dbf05 100644
--- a/drivers/spi/spi-mt65xx.c
+++ b/drivers/spi/spi-mt65xx.c
@@ -323,7 +323,8 @@ static int mtk_spi_fifo_transfer(struct spi_master *master,
                                  struct spi_device *spi,
                                  struct spi_transfer *xfer)
 {
-        int cnt;
+        int cnt, remainder;
+        u32 reg_val;
         struct mtk_spi *mdata = spi_master_get_devdata(master);
 
         mdata->cur_transfer = xfer;
@@ -331,12 +332,16 @@ static int mtk_spi_fifo_transfer(struct spi_master *master,
         mtk_spi_prepare_transfer(master, xfer);
         mtk_spi_setup_packet(master);
 
-        if (xfer->len % 4)
-                cnt = xfer->len / 4 + 1;
-        else
-                cnt = xfer->len / 4;
+        cnt = xfer->len / 4;
         iowrite32_rep(mdata->base + SPI_TX_DATA_REG, xfer->tx_buf, cnt);
 
+        remainder = xfer->len % 4;
+        if (remainder > 0) {
+                reg_val = 0;
+                memcpy(&reg_val, xfer->tx_buf + (cnt * 4), remainder);
+                writel(reg_val, mdata->base + SPI_TX_DATA_REG);
+        }
+
         mtk_spi_enable_transfer(master);
 
         return 1;
@@ -418,7 +423,7 @@ static int mtk_spi_setup(struct spi_device *spi)
 
 static irqreturn_t mtk_spi_interrupt(int irq, void *dev_id)
 {
-        u32 cmd, reg_val, cnt;
+        u32 cmd, reg_val, cnt, remainder;
         struct spi_master *master = dev_id;
         struct mtk_spi *mdata = spi_master_get_devdata(master);
         struct spi_transfer *trans = mdata->cur_transfer;
@@ -431,12 +436,15 @@ static irqreturn_t mtk_spi_interrupt(int irq, void *dev_id)
 
         if (!master->can_dma(master, master->cur_msg->spi, trans)) {
                 if (trans->rx_buf) {
-                        if (mdata->xfer_len % 4)
-                                cnt = mdata->xfer_len / 4 + 1;
-                        else
-                                cnt = mdata->xfer_len / 4;
+                        cnt = mdata->xfer_len / 4;
                         ioread32_rep(mdata->base + SPI_RX_DATA_REG,
                                      trans->rx_buf, cnt);
+                        remainder = mdata->xfer_len % 4;
+                        if (remainder > 0) {
+                                reg_val = readl(mdata->base + SPI_RX_DATA_REG);
+                                memcpy(trans->rx_buf + (cnt * 4),
+                                        &reg_val, remainder);
+                        }
                 }
                 spi_finalize_current_transfer(master);
                 return IRQ_HANDLED;