[PATCH] net: prestera: avoid overreading a short firmware tail

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

prestera_ldr_send() writes the firmware in 32-bit words even when the final
chunk is not four-byte aligned. The last iteration then reads a full u32
from a one-to-three-byte tail.

Reserve the aligned ring space, use unaligned-safe full-word loads, and
zero-pad a partial final word without reading beyond the firmware image.

Fixes: 4c2703dfd7fa ("net: marvell: prestera: Add PCI interface support")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 drivers/net/ethernet/marvell/prestera/prestera_pci.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/marvell/prestera/prestera_pci.c b/drivers/net/ethernet/marvell/prestera/prestera_pci.c
index 1ad0e62a8433b..9b3d6e5a81d1c 100644
--- a/drivers/net/ethernet/marvell/prestera/prestera_pci.c
+++ b/drivers/net/ethernet/marvell/prestera/prestera_pci.c
@@ -589,17 +589,26 @@ static u8 __iomem *prestera_ldr_wr_ptr(struct prestera_fw *fw)
 
 static int prestera_ldr_send(struct prestera_fw *fw, const u8 *buf, size_t len)
 {
+	size_t write_len = ALIGN(len, sizeof(u32));
+	size_t i;
 	int err;
-	int i;
 
-	err = prestera_ldr_wait_buf(fw, len);
+	err = prestera_ldr_wait_buf(fw, write_len);
 	if (err) {
 		dev_err(fw->dev.dev, "failed wait for sending firmware\n");
 		return err;
 	}
 
-	for (i = 0; i < len; i += 4) {
-		writel_relaxed(*(u32 *)(buf + i), prestera_ldr_wr_ptr(fw));
+	for (i = 0; i + sizeof(u32) <= len; i += sizeof(u32)) {
+		writel_relaxed(get_unaligned((u32 *)(buf + i)),
+			       prestera_ldr_wr_ptr(fw));
+		prestera_ldr_wr_idx_move(fw, 4);
+	}
+	if (i < len) {
+		u32 last = 0;
+
+		memcpy(&last, buf + i, len - i);
+		writel_relaxed(last, prestera_ldr_wr_ptr(fw));
 		prestera_ldr_wr_idx_move(fw, 4);
 	}

base-commit: 08dbfad3f5040f5bdb6c529da20d6d4e81fefd72
-- 
2.50.1