[PATCH net v2] net: prestera: avoid overreading a short firmware tail

[Pengpeng Hou <hppiscas@163.com>]

prestera_ldr_fw_send() passes complete 1024-byte blocks to the loader
and then sends fw_size - pos as the final chunk. Firmware header validation
does not require the payload size to be a multiple of four. Consequently
that last chunk can end with one to three bytes, while prestera_ldr_send()
still loads a full u32 from it and transfers bytes beyond the supplied
firmware image to the device.

Reserve space for the rounded-up transfer, use unaligned-safe full-word
loads, and construct the final word from only the remaining bytes with
zero padding. The firmware image-size register still describes the exact
payload size. Preserve the existing native-word load and writel_relaxed()
byte-order convention.

The issue was found by our static-analysis tool and manually reviewed.

Fixes: 4c2703dfd7fa ("net: marvell: prestera: Add PCI interface support")
Assisted-by: gpt 5
Signed-off-by: Pengpeng Hou <hppiscas@163.com>
---
Changes since v1:
- explain why a short final chunk reaches the loader, as Andrew requested
- include linux/unaligned.h to fix the reported undeclared get_unaligned()
- use a const full-word source pointer and sizeof(u32) for index movement
- rebase on current mainline

Previous version:
https://lore.kernel.org/all/20260830142404.37663-1-pengpeng@iscas.ac.cn/

 .../net/ethernet/marvell/prestera/prestera_pci.c   |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/marvell/prestera/prestera_pci.c b/drivers/net/ethernet/marvell/prestera/prestera_pci.c
index 1ad0e62a8433ba91a9c019aa7f277c6c9f65f58e..4492c35ea5d388ef485f424d88fc1f9b0f7ad29e 100644
--- a/drivers/net/ethernet/marvell/prestera/prestera_pci.c
+++ b/drivers/net/ethernet/marvell/prestera/prestera_pci.c
@@ -6,6 +6,7 @@
 #include <linux/device.h>
 #include <linux/firmware.h>
 #include <linux/iopoll.h>
+#include <linux/unaligned.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/pci.h>
@@ -589,18 +590,27 @@ 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));
-		prestera_ldr_wr_idx_move(fw, 4);
+	for (i = 0; i + sizeof(u32) <= len; i += sizeof(u32)) {
+		writel_relaxed(get_unaligned((const u32 *)(buf + i)),
+			       prestera_ldr_wr_ptr(fw));
+		prestera_ldr_wr_idx_move(fw, sizeof(u32));
+	}
+	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, sizeof(u32));
 	}
 
 	prestera_ldr_wr_idx_commit(fw);

base-commit: 4056b3c9d3c92ea45955641dbafeb9b960e146ef