hw/misc/aspeed_hace: Fix buffer overflow in has_padding function

The maximum padding size is either 64 or 128 bytes and should always be smaller
than "req_len". If "padding_size" exceeds "req_len", then
"req_len - padding_size" underflows due to "uint32_t" data type, leading to a
large incorrect value (e.g., `0xFFXXXXXX`). This causes an out-of-bounds memory
access, potentially leading to a buffer overflow.

Added a check to ensure "padding_size" does not exceed "req_len" before
computing "pad_offset". This prevents "req_len - padding_size" from underflowing
and avoids accessing invalid memory.

Signed-off-by: Jamin Lin <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Fixes: 5cd7d85 ("aspeed/hace: Support AST2600 HACE ")
Link: https://lore.kernel.org/qemu-devel/[email protected]
Signed-off-by: Cédric Le Goater <[email protected]>

Author: jamin-aspeed

hw/misc/aspeed_hace.c

@@ -128,6 +128,11 @@ static bool has_padding(AspeedHACEState *s, struct iovec *iov,
     if (*total_msg_len <= s->total_req_len) {
         uint32_t padding_size = s->total_req_len - *total_msg_len;
         uint8_t *padding = iov->iov_base;
+
+        if (padding_size > req_len) {
+            return false;
+        }
+
         *pad_offset = req_len - padding_size;
         if (padding[*pad_offset] == 0x80) {
             return true;