Now that the EFI stub boot flow no longer relies on memory that is executable and writable at the same time, we can reorganize the PE/COFF view of the kernel image and expose the decompressor binary's code and r/o data as a .text section and data/bss as a .data section, using 4k alignment and limited permissions. Doing so is necessary for compatibility with hardening measures that are being rolled out on x86 PCs built to run Windows (i.e., the majority of them). The EFI boot environment that the Linux EFI stub executes in is especially sensitive to safety issues, given that a vulnerability in the loader of one OS can be abused to attack another. In true x86 fashion, this is more complicated than on other architectures, which have implemented this code/data split with 4k alignment from the beginning. The complicating factor here is that the boot image consists of two different parts, which are stitched together and fixed up using a special build tool. The first three patches simplify the x86 EFI stub code so it does not even bother reading the setup header from the image - passing arguments this way is not supported by EFI boot anyway. Then, the bzImage is simplified and reorganized, primarily by: - dropping the ancient 'bugger off' message occupying much of the header space - using a fixed size of 16k for the setup block - setting header values from asm instead of via the build tool Finally, the payload is split into .text and .data, and the section and file alignment increased to 4k/512 respectively. The only remaining task performed by the build tool is generating the CRC-32 that is fundamentally broken in practice and never used, so that is dropped entirely at the end. This supersedes the work proposed by Evgeniy last year, which did a major rewrite of the build tool in order to clean it up, before updating it to generate the new 4k aligned image layout. As this series proves, the build tool is mostly unnecessary, and we have too many of those already. Cc: Evgeniy Baskov <baskov@xxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Jones <pjones@xxxxxxxxxx> Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Marvin Häuser <mhaeuser@xxxxxxxxx> Ard Biesheuvel (17): x86/efi: Drop EFI stub .bss from .data section x86/efi: Disregard setup header of loaded image x86/efi: Drop alignment flags from PE section headers x86/boot: Remove the 'bugger off' message x86/boot: Omit compression buffer from PE/COFF image memory footprint x86/boot: Drop redundant code setting the root device x86/boot: Grab kernel_info offset from zoffset header directly x86/boot: Drop references to startup_64 x86/boot: Set EFI handover offset directly in header asm x86/boot: Drop workaround for binutils 2.14 in linker script ASSERTs x86/boot: Use fixed size of 16k for setup block x86/boot: Derive file size from _edata symbol x86/boot: Construct PE/COFF .text section from assembler x86/boot: Drop PE/COFF .reloc section x86/boot: Split off PE/COFF .data section x86/boot: Increase section and file alignment to 4k/512 x86/boot: Drop CRC-32 checksum and the build tool that generates it Documentation/arch/x86/boot.rst | 10 - arch/x86/boot/Makefile | 12 +- arch/x86/boot/compressed/vmlinux.lds.S | 5 +- arch/x86/boot/header.S | 217 ++++----- arch/x86/boot/setup.ld | 21 +- arch/x86/boot/tools/.gitignore | 2 - arch/x86/boot/tools/build.c | 502 -------------------- drivers/firmware/efi/libstub/Makefile | 7 - drivers/firmware/efi/libstub/x86-stub.c | 46 +- 9 files changed, 113 insertions(+), 709 deletions(-) delete mode 100644 arch/x86/boot/tools/.gitignore delete mode 100644 arch/x86/boot/tools/build.c -- 2.39.2
