hw/i386/elfboot: allocate "header" in heap

hw/i386/elfboot: allocate "header" in heap

In x86_load_linux(), we were using a stack-allocated array as data for
fw_cfg_add_bytes(). Since the latter just takes a reference to the
pointer instead of copying the data, it can happen that the contents
have been overridden by the time the guest attempts to access them.

Instead of using the stack-allocated array, allocate some memory from
the heap, copy the contents of the array, and use it for fw_cfg.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241109053748.13183-1-slp@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>