loader/arm64/linux: Account for COFF headers appearing at unexpected offsets

The way we load the Linux and PE/COFF image headers depends on a fixed
placement of the COFF header at offset 0x40 into the file. This is
a reasonable default, given that this is where Linux emits it today.
However, in order to comply with the PE/COFF spec, which allows this
header to appear anywhere in the file, let's ensure that we read the
header from where it actually appears in the file if it is not located
at offset 0x40.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 3733a69d6e362618670904c8903ba2516217b0db..754db84a96cf21fcf369f8f5c1825504755e94f2 100644 (file)
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -63,6 +63,21 @@ grub_arch_efi_linux_load_image_header (grub_file_t file,
   grub_dprintf ("linux", "UEFI stub kernel:\n");
   grub_dprintf ("linux", "PE/COFF header @ %08x\n", lh->hdr_offset);
 
+  /*
+   * The PE/COFF spec permits the COFF header to appear anywhere in the file, so
+   * we need to double check whether it was where we expected it, and if not, we
+   * must load it from the correct offset into the pe_image_header field of
+   * struct linux_arch_kernel_header.
+   */
+  if ((grub_uint8_t *) lh + lh->hdr_offset != (grub_uint8_t *) &lh->pe_image_header)
+    {
+      if (grub_file_seek (file, lh->hdr_offset) == (grub_off_t) -1
+          || grub_file_read (file, &lh->pe_image_header,
+                             sizeof (struct grub_pe_image_header))
+             != sizeof (struct grub_pe_image_header))
+        return grub_error (GRUB_ERR_FILE_READ_ERROR, "failed to read COFF image header");
+    }
+
   return GRUB_ERR_NONE;
 }