linux-toradex.git/arch/x86/boot/tools, branch master Linux kernel for Apalis and Colibri modules x86/boot: Drop CRC-32 checksum and the build tool that generates it 2025-03-07T22:59:10+00:00 Ard Biesheuvel ardb@kernel.org 2025-03-07T16:48:02+00:00 9c54baab4401db249d6938806b812231e0259380 Apart from some sanity checks on the size of setup.bin, the only remaining task carried out by the arch/x86/boot/tools/build.c build tool is generating the CRC-32 checksum of the bzImage. This feature was added in commit 7d6e737c8d2698b6 ("x86: add a crc32 checksum to the kernel image.") without any motivation (or any commit log text, for that matter). This checksum is not verified by any known bootloader, and given that a) the checksum of the entire bzImage is reported by most tools (zlib, rhash) as 0xffffffff and not 0x0 as documented, b) the checksum is corrupted when the image is signed for secure boot, which means that no distro ships x86 images with valid CRCs, it seems quite unlikely that this checksum is being used, so let's just drop it, along with the tool that generates it. Instead, use simple file concatenation and truncation to combine the two pieces into bzImage, and replace the checks on the size of the setup block with a couple of ASSERT()s in the linker script. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ian Campbell <ijc@hellion.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20250307164801.885261-2-ardb+git@google.com 
Apart from some sanity checks on the size of setup.bin, the only
remaining task carried out by the arch/x86/boot/tools/build.c build tool
is generating the CRC-32 checksum of the bzImage. This feature was added
in commit

  7d6e737c8d2698b6 ("x86: add a crc32 checksum to the kernel image.")

without any motivation (or any commit log text, for that matter). This
checksum is not verified by any known bootloader, and given that

 a) the checksum of the entire bzImage is reported by most tools (zlib,
    rhash) as 0xffffffff and not 0x0 as documented,

 b) the checksum is corrupted when the image is signed for secure boot,
    which means that no distro ships x86 images with valid CRCs,

it seems quite unlikely that this checksum is being used, so let's just
drop it, along with the tool that generates it.

Instead, use simple file concatenation and truncation to combine the two
pieces into bzImage, and replace the checks on the size of the setup
block with a couple of ASSERT()s in the linker script.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ian Campbell <ijc@hellion.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250307164801.885261-2-ardb+git@google.com
x86/boot: Increase section and file alignment to 4k/512 2023-09-17T17:48:44+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:32+00:00 3e3eabe26dc88692d34cf76ca0e0dd331481cc15 Align x86 with other EFI architectures, and increase the section alignment to the EFI page size (4k), so that firmware is able to honour the section permission attributes and map code read-only and data non-executable. There are a number of requirements that have to be taken into account: - the sign tools get cranky when there are gaps between sections in the file view of the image - the virtual offset of each section must be aligned to the image's section alignment - the file offset *and size* of each section must be aligned to the image's file alignment - the image size must be aligned to the section alignment - each section's virtual offset must be greater than or equal to the size of the headers. In order to meet all these requirements, while avoiding the need for lots of padding to accommodate the .compat section, the latter is placed at an arbitrary offset towards the end of the image, but aligned to the minimum file alignment (512 bytes). The space before the .text section is therefore distributed between the PE header, the .setup section and the .compat section, leaving no gaps in the file coverage, making the signing tools happy. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-18-ardb@google.com 
Align x86 with other EFI architectures, and increase the section
alignment to the EFI page size (4k), so that firmware is able to honour
the section permission attributes and map code read-only and data
non-executable.

There are a number of requirements that have to be taken into account:
- the sign tools get cranky when there are gaps between sections in the
  file view of the image
- the virtual offset of each section must be aligned to the image's
  section alignment
- the file offset *and size* of each section must be aligned to the
  image's file alignment
- the image size must be aligned to the section alignment
- each section's virtual offset must be greater than or equal to the
  size of the headers.

In order to meet all these requirements, while avoiding the need for
lots of padding to accommodate the .compat section, the latter is placed
at an arbitrary offset towards the end of the image, but aligned to the
minimum file alignment (512 bytes). The space before the .text section
is therefore distributed between the PE header, the .setup section and
the .compat section, leaving no gaps in the file coverage, making the
signing tools happy.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-18-ardb@google.com
x86/boot: Drop PE/COFF .reloc section 2023-09-17T17:48:43+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:30+00:00 fa5750521e0a4efbc1af05223da9c4bbd6c21c83 Ancient buggy EFI loaders may have required a .reloc section to be present at some point in time, but this has not been true for a long time so the .reloc section can just be dropped. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-16-ardb@google.com 
Ancient buggy EFI loaders may have required a .reloc section to be
present at some point in time, but this has not been true for a long
time so the .reloc section can just be dropped.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-16-ardb@google.com
x86/boot: Construct PE/COFF .text section from assembler 2023-09-17T17:48:43+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:29+00:00 efa089e63b56bdc5eca754b995cb039dd7a5457e Now that the size of the setup block is visible to the assembler, it is possible to populate the PE/COFF header fields from the asm code directly, instead of poking the values into the binary using the build tool. This will make it easier to reorganize the section layout without having to tweak the build tool in lockstep. This change has no impact on the resulting bzImage binary. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-15-ardb@google.com 
Now that the size of the setup block is visible to the assembler, it is
possible to populate the PE/COFF header fields from the asm code
directly, instead of poking the values into the binary using the build
tool. This will make it easier to reorganize the section layout without
having to tweak the build tool in lockstep.

This change has no impact on the resulting bzImage binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-15-ardb@google.com
x86/boot: Derive file size from _edata symbol 2023-09-17T17:48:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:28+00:00 aeb92067f6ae994b541d7f9752fe54ed3d108bcc Tweak the linker script so that the value of _edata represents the decompressor binary's file size rounded up to the appropriate alignment. This removes the need to calculate it in the build tool, and will make it easier to refer to the file size from the header directly in subsequent changes to the PE header layout. While adding _edata to the sed regex that parses the compressed vmlinux's symbol list, tweak the regex a bit for conciseness. This change has no impact on the resulting bzImage binary when configured with CONFIG_EFI_STUB=y. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-14-ardb@google.com 
Tweak the linker script so that the value of _edata represents the
decompressor binary's file size rounded up to the appropriate alignment.
This removes the need to calculate it in the build tool, and will make
it easier to refer to the file size from the header directly in
subsequent changes to the PE header layout.

While adding _edata to the sed regex that parses the compressed
vmlinux's symbol list, tweak the regex a bit for conciseness.

This change has no impact on the resulting bzImage binary when
configured with CONFIG_EFI_STUB=y.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-14-ardb@google.com
x86/boot: Define setup size in linker script 2023-09-17T17:48:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:27+00:00 093ab258e3fb1d1d3afdfd4a69403d44ce90e360 The setup block contains the real mode startup code that is used when booting from a legacy BIOS, along with the boot_params/setup_data that is used by legacy x86 bootloaders to pass the command line and initial ramdisk parameters, among other things. The setup block also contains the PE/COFF header of the entire combined image, which includes the compressed kernel image, the decompressor and the EFI stub. This PE header describes the layout of the executable image in memory, and currently, the fact that the setup block precedes it makes it rather fiddly to get the right values into the right place in the final image. Let's make things a bit easier by defining the setup_size in the linker script so it can be referenced from the asm code directly, rather than having to rely on the build tool to calculate it. For the time being, add 64 bytes of fixed padding for the .reloc and .compat sections - this will be removed in a subsequent patch after the PE/COFF header has been reorganized. This change has no impact on the resulting bzImage binary when configured with CONFIG_EFI_MIXED=y. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-13-ardb@google.com 
The setup block contains the real mode startup code that is used when
booting from a legacy BIOS, along with the boot_params/setup_data that
is used by legacy x86 bootloaders to pass the command line and initial
ramdisk parameters, among other things.

The setup block also contains the PE/COFF header of the entire combined
image, which includes the compressed kernel image, the decompressor and
the EFI stub.

This PE header describes the layout of the executable image in memory,
and currently, the fact that the setup block precedes it makes it rather
fiddly to get the right values into the right place in the final image.

Let's make things a bit easier by defining the setup_size in the linker
script so it can be referenced from the asm code directly, rather than
having to rely on the build tool to calculate it. For the time being,
add 64 bytes of fixed padding for the .reloc and .compat sections - this
will be removed in a subsequent patch after the PE/COFF header has been
reorganized.

This change has no impact on the resulting bzImage binary when
configured with CONFIG_EFI_MIXED=y.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-13-ardb@google.com
x86/boot: Set EFI handover offset directly in header asm 2023-09-17T17:48:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:26+00:00 eac956345f99dda3d68f4ae6cf7b494105e54780 The offsets of the EFI handover entrypoints are available to the assembler when constructing the header, so there is no need to set them from the build tool afterwards. This change has no impact on the resulting bzImage binary. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-12-ardb@google.com 
The offsets of the EFI handover entrypoints are available to the
assembler when constructing the header, so there is no need to set them
from the build tool afterwards.

This change has no impact on the resulting bzImage binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-12-ardb@google.com
x86/boot: Grab kernel_info offset from zoffset header directly 2023-09-17T17:48:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-15T17:16:25+00:00 2e765c02dcbfc2a8a4527c621a84b9502f6b9bd2 Instead of parsing zoffset.h and poking the kernel_info offset value into the header from the build tool, just grab the value directly in the asm file that describes this header. This change has no impact on the resulting bzImage binary. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230915171623.655440-11-ardb@google.com 
Instead of parsing zoffset.h and poking the kernel_info offset value
into the header from the build tool, just grab the value directly in the
asm file that describes this header.

This change has no impact on the resulting bzImage binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-11-ardb@google.com
x86/boot: Drop references to startup_64 2023-09-15T09:18:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-12T09:00:59+00:00 b618d31f112bea3d2daea19190d63e567f32a4db The x86 boot image generation tool assign a default value to startup_64 and subsequently parses the actual value from zoffset.h but it never actually uses the value anywhere. So remove this code. This change has no impact on the resulting bzImage binary. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230912090051.4014114-25-ardb@google.com 
The x86 boot image generation tool assign a default value to startup_64
and subsequently parses the actual value from zoffset.h but it never
actually uses the value anywhere. So remove this code.

This change has no impact on the resulting bzImage binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230912090051.4014114-25-ardb@google.com
x86/boot: Drop redundant code setting the root device 2023-09-15T09:18:42+00:00 Ard Biesheuvel ardb@kernel.org 2023-09-12T09:00:57+00:00 7448e8e5d15a3c4df649bf6d6d460f78396f7e1e The root device defaults to 0,0 and is no longer configurable at build time [0], so there is no need for the build tool to ever write to this field. [0] 079f85e624189292 ("x86, build: Do not set the root_dev field in bzImage") This change has no impact on the resulting bzImage binary. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230912090051.4014114-23-ardb@google.com 
The root device defaults to 0,0 and is no longer configurable at build
time [0], so there is no need for the build tool to ever write to this
field.

[0] 079f85e624189292 ("x86, build: Do not set the root_dev field in bzImage")

This change has no impact on the resulting bzImage binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230912090051.4014114-23-ardb@google.com