kernel.git/arch/x86/boot/header.S, branch linux-6.15.y

efi/x86: Set the PE/COFF header's NX compat flag unconditionally

2024-02-28T13:23:55Z

Now that the proper section and file alignment is used, and the EFI memory attributes protocol to manage executable permissions where needed is invoked, set the NX compat flag unconditionally. [ bp: Remove the "we"s. ] Signed-off-by: Ard Biesheuvel Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20240116085347.2193966-2-ardb+git@google.com

x86/efistub: Use 1:1 file:memory mapping for PE/COFF .compat section

2024-02-05T10:24:51Z

The .compat section is a dummy PE section that contains the address of the 32-bit entrypoint of the 64-bit kernel image if it is bootable from 32-bit firmware (i.e., CONFIG_EFI_MIXED=y) This section is only 8 bytes in size and is only referenced from the loader, and so it is placed at the end of the memory view of the image, to avoid the need for padding it to 4k, which is required for sections appearing in the middle of the image. Unfortunately, this violates the PE/COFF spec, and even if most EFI loaders will work correctly (including the Tianocore reference implementation), PE loaders do exist that reject such images, on the basis that both the file and memory views of the file contents should be described by the section headers in a monotonically increasing manner without leaving any gaps. So reorganize the sections to avoid this issue. This results in a slight padding overhead (< 4k) which can be avoided if desired by disabling CONFIG_EFI_MIXED (which is only needed in rare cases these days) Fixes: 3e3eabe26dc8 ("x86/boot: Increase section and file alignment to 4k/512") Reported-by: Mike Beaton Link: https://lkml.kernel.org/r/CAHzAAWQ6srV6LVNdmfbJhOwhBw5ZzxxZZ07aHt9oKkfYAdvuQQ%40mail.gmail.com Signed-off-by: Ard Biesheuvel

x86/boot: Increase section and file alignment to 4k/512

2023-09-17T17:48:44Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-18-ardb@google.com

x86/boot: Split off PE/COFF .data section

2023-09-17T17:48:43Z

Describe the code and data of the decompressor binary using separate .text and .data PE/COFF sections, so that we will be able to map them using restricted permissions once we increase the section and file alignment sufficiently. This avoids the need for memory mappings that are writable and executable at the same time, which is something that is best avoided for security reasons. Signed-off-by: Ard Biesheuvel Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-17-ardb@google.com

x86/boot: Drop PE/COFF .reloc section

2023-09-17T17:48:43Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-16-ardb@google.com

x86/boot: Construct PE/COFF .text section from assembler

2023-09-17T17:48:43Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-15-ardb@google.com

x86/boot: Derive file size from _edata symbol

2023-09-17T17:48:42Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-14-ardb@google.com

x86/boot: Define setup size in linker script

2023-09-17T17:48:42Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-13-ardb@google.com

x86/boot: Set EFI handover offset directly in header asm

2023-09-17T17:48:42Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-12-ardb@google.com

x86/boot: Grab kernel_info offset from zoffset header directly

2023-09-17T17:48:42Z

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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230915171623.655440-11-ardb@google.com