multiboot: Reject kernels exceeding the address space

The code path where mh_load_end_addr is non-zero in the Multiboot
header checks that mh_load_end_addr >= mh_load_addr and so
mb_load_size is checked.  However, mb_load_size is not checked when
calculated from the file size, when mh_load_end_addr is 0.

If the kernel binary size is larger than can fit in the address space
after load_addr, we ended up with a kernel_size that is smaller than
load_size, which means that we read the file into a too small buffer.

Add a check to reject kernel files with such Multiboot headers.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Jack Schwartz <jack.schwartz@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/hw/i386/multiboot.c b/hw/i386/multiboot.c
index b906426..1e215bf 100644
--- a/hw/i386/multiboot.c
+++ b/hw/i386/multiboot.c
@@ -247,6 +247,10 @@ int load_multiboot(FWCfgState *fw_cfg,
             }
             mb_load_size = kernel_file_size - mb_kernel_text_offset;
         }
+        if (mb_load_size > UINT32_MAX - mh_load_addr) {
+            error_report("kernel does not fit in address space");
+            exit(1);
+        }
         if (mh_bss_end_addr) {
             if (mh_bss_end_addr < (mh_load_addr + mb_load_size)) {
                 error_report("invalid bss_end_addr address");