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[resend,5/9] linux/arm: account for COFF headers appearing at unexpected offsets

Message ID 20220818085540.2075028-6-ardb@kernel.org
State New
Headers show
Series linux: implement LoadFile2 initrd loading | expand

Commit Message

Ard Biesheuvel Aug. 18, 2022, 8:55 a.m. UTC
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>
---
 grub-core/loader/arm64/linux.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
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Patch

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 7c0f17cf933d..56ba8d0a6ea3 100644
--- 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 coff_image_header field of
+   * struct linux_arch_kernel_header.
+   */
+  if ((grub_uint8_t *) lh + lh->hdr_offset != (grub_uint8_t *) &lh->coff_image_header)
+    {
+      grub_file_seek (file, lh->hdr_offset);
+
+      if (grub_file_read (file, &lh->coff_image_header, sizeof(struct grub_coff_image_header))
+         != sizeof(struct grub_coff_image_header))
+       return grub_error(GRUB_ERR_FILE_READ_ERROR, "failed to read COFF image header");
+    }
+
   return GRUB_ERR_NONE;
 }