[PATCH resend 3/9] arm64/linux: Remove magic number header field check

Ard Biesheuvel
2022-08-18T08:55:59Z

The 'ARM\x64' magic number in the file header identifies an image as one
that implements the bare metal boot protocol, allowing the loader to
simply move the file to a suitably aligned address in memory, with
sufficient headroom for the trailing .bss segment (the required memory
size is described in the header as well).

Note of this matters for GRUB, as it only supports EFI boot. EFI does
not care about this magic number, and nor should GRUB: this prevents us
from booting other PE linux images, such as the generic EFI zboot
decompressor, which is a pure PE/COFF image, and does not implement the
bare metal boot protocol.

So drop the magic number check.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
grub-core/loader/arm64/linux.c | 3 ---
include/grub/arm/linux.h | 1 -
include/grub/arm64/linux.h | 1 -
3 files changed, 5 deletions(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index aed7a200b848..b5b559c236e0 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -51,9 +51,6 @@ static grub_addr_t initrd_end;
grub_err_t
grub_arch_efi_linux_check_image (struct linux_arch_kernel_header * lh)
{
- if (lh->magic != GRUB_LINUX_ARMXX_MAGIC_SIGNATURE)
- return grub_error(GRUB_ERR_BAD_OS, "invalid magic number");
-
if ((lh->code0 & 0xffff) != GRUB_PE32_MAGIC)
return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
N_("plain image kernel not supported - rebuild with CONFIG_(U)EFI_STUB enabled"));
diff --git a/include/grub/arm/linux.h b/include/grub/arm/linux.h
index bcd5a7eb186e..bfab334dd87f 100644
--- a/include/grub/arm/linux.h
+++ b/include/grub/arm/linux.h
@@ -35,7 +35,6 @@ struct linux_arm_kernel_header {
};

#if defined(__arm__)
-# define GRUB_LINUX_ARMXX_MAGIC_SIGNATURE GRUB_LINUX_ARM_MAGIC_SIGNATURE
# define linux_arch_kernel_header linux_arm_kernel_header
#endif

diff --git a/include/grub/arm64/linux.h b/include/grub/arm64/linux.h
index 7e22b4ab6990..96f1494e05a2 100644
--- a/include/grub/arm64/linux.h
+++ b/include/grub/arm64/linux.h
@@ -39,7 +39,6 @@ struct linux_arm64_kernel_header
};

#if defined(__aarch64__)
-# define GRUB_LINUX_ARMXX_MAGIC_SIGNATURE GRUB_LINUX_ARM64_MAGIC_SIGNATURE
# define linux_arch_kernel_header linux_arm64_kernel_header
#endif

--
2.35.1