[PATCH] hw/core/loader: Fix possible crash in rom_copy()

[Thomas Huth <thuth@redhat.com>]

Both, "rom->addr" and "addr" are derived from the binary image
that can be loaded with the "-kernel" paramer. The code in
rom_copy() then calculates:

    d = dest + (rom->addr - addr);

and uses "d" as destination in a memcpy() some lines later. Now with
bad kernel images, it is possible that rom->addr is smaller than addr,
thus "rom->addr - addr" gets negative and the memcpy() then tries to
copy contents from the image to a bad memory location. In the best case,
this just crashes QEMU, in the worst case, this could maybe be used to
inject code from the kernel image into the QEMU binary, so we better fix
it with an additional sanity check here.

Cc: qemu-stable@nongnu.org
Reported-by: Guangming Liu
Buglink: https://bugs.launchpad.net/qemu/+bug/1844635
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 hw/core/loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/core/loader.c b/hw/core/loader.c
index 0d60219364..5099f27dc8 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -1281,7 +1281,7 @@ int rom_copy(uint8_t *dest, hwaddr addr, size_t size)
         if (rom->addr + rom->romsize < addr) {
             continue;
         }
-        if (rom->addr > end) {
+        if (rom->addr > end || rom->addr < addr) {
             break;
         }
 
-- 
2.18.1