x86/loader: only patch linux kernels

If the binary loaded via -kernel is *not* a linux kernel (in which
case protocol == 0), do not patch the linux kernel header fields.

It's (a) pointless and (b) might break binaries by random patching
and (c) changes the binary hash which in turn breaks secure boot
verification.

Background: OVMF happily loads and runs not only linux kernels but
any efi binary via direct kernel boot.

Note: Breaking the secure boot verification is a problem for linux
kernels too, but fixed that is left for another day ...

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-ID: <20240905141211.1253307-3-kraxel@redhat.com>

hw/i386/x86-common.c

@@ -945,7 +945,7 @@ void x86_load_linux(X86MachineState *x86ms,
      * kernel on the other side of the fw_cfg interface matches the hash of the
      * file the user passed in.
      */
-    if (!sev_enabled()) {
+    if (!sev_enabled() && protocol > 0) {
         memcpy(setup, header, MIN(sizeof(header), setup_size));
     }