[PATCH] x86: boot: Fix EFI stub alignment

[PATCH] x86: boot: Fix EFI stub alignment

[Ben Hutchings]

[-- Attachment #1: Type: text/plain, Size: 1355 bytes --]

We currently align the end of the compressed image to a multiple of
16.  However the PE-COFF header included in the EFI stub says that the
file alignment is 32 bytes, and when adding an EFI signature to the
file it must first be padded to this alignment.

sbsigntool commands warn about this:

    warning: file-aligned section .text extends beyond end of file
    warning: checksum areas are greater than image size. Invalid section table?

Worse, pesign-at least when creating a detached signature—uses the
hash of the unpadded file, resulting in an invalid signature if
padding is required.

Avoid both these problems by increasing alignment to 32 bytes when
CONFIG_EFI_STUB is enabled.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -391,6 +391,13 @@ int main(int argc, char ** argv)
 		die("Unable to mmap '%s': %m", argv[2]);
 	/* Number of 16-byte paragraphs, including space for a 4-byte CRC */
 	sys_size = (sz + 15 + 4) / 16;
+#ifdef CONFIG_EFI_STUB
+	/*
+	 * COFF requires minimum 32-byte alignment of sections, and
+	 * adding a signature is problematic without that alignment.
+	 */
+	sys_size = (sys_size + 1) & ~1;
+#endif
 
 	/* Patch the setup code with the appropriate size parameters */
 	buf[0x1f1] = setup_sectors-1;

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]

Re: [PATCH] x86: boot: Fix EFI stub alignment

[Ard Biesheuvel]

On 16 September 2018 at 08:22, Ben Hutchings <ben@decadent.org.uk> wrote:
> We currently align the end of the compressed image to a multiple of
> 16.  However the PE-COFF header included in the EFI stub says that the
> file alignment is 32 bytes, and when adding an EFI signature to the
> file it must first be padded to this alignment.
>
> sbsigntool commands warn about this:
>
>     warning: file-aligned section .text extends beyond end of file
>     warning: checksum areas are greater than image size. Invalid section table?
>
> Worse, pesign-at least when creating a detached signature—uses the
> hash of the unpadded file, resulting in an invalid signature if
> padding is required.
>
> Avoid both these problems by increasing alignment to 32 bytes when
> CONFIG_EFI_STUB is enabled.
>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---

Thanks, queued in efi/next.


> --- a/arch/x86/boot/tools/build.c
> +++ b/arch/x86/boot/tools/build.c
> @@ -391,6 +391,13 @@ int main(int argc, char ** argv)
>                 die("Unable to mmap '%s': %m", argv[2]);
>         /* Number of 16-byte paragraphs, including space for a 4-byte CRC */
>         sys_size = (sz + 15 + 4) / 16;
> +#ifdef CONFIG_EFI_STUB
> +       /*
> +        * COFF requires minimum 32-byte alignment of sections, and
> +        * adding a signature is problematic without that alignment.
> +        */
> +       sys_size = (sys_size + 1) & ~1;
> +#endif
>
>         /* Patch the setup code with the appropriate size parameters */
>         buf[0x1f1] = setup_sectors-1;