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

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. This could
maybe be used to inject code from a 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
Message-Id: <20190925130331.27825-1-thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit e423455c4f23a1a828901c78fe6d03b7dde79319)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/hw/core/loader.c b/hw/core/loader.c
index fe5cb24122559dfdb7b5648fb5e2fc90b3cbc56a..4ef2095247105afa202a28c56e7ad46a7266175f 100644 (file)
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -1240,7 +1240,7 @@ 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;
         }