This series is conceptually a combination of Evgeny's series [0] and mine [1], both of which attempt to make the early decompressor code more amenable to executing in the EFI environment with stricter handling of memory permissions. My series [1] implemented zboot for x86, by getting rid of the entire x86 decompressor, and replacing it with existing EFI code that does the same but in a generic way. The downside of this is that only EFI boot is supported, making it unviable for distros, which need to support BIOS boot and hybrid EFI boot modes that omit the EFI stub. Evgeny's series [0] adapted the entire decompressor code flow to allow it to execute in the EFI context as well as the bare metal context, and this involves changes to the 1:1 mapping code and the page fault handlers etc, none of which are really needed when doing EFI boot in the first place. So this series attempts to occupy the middle ground here: it makes minimal changes to the existing decompressor so some of it can be called from the EFI stub. Then, it reimplements the EFI boot flow to decompress the kernel and boot it directly, without relying on the trampoline code, page table code or page fault handling code. This allows us to get rid of quite a bit of unsavory EFI stub code, and replace it with two clear invocations of the EFI firmware APIs to clear NX restrictions from allocations that have been populated with executable code. The only code that is being reused is the decompression library itself, along with the minimal ELF parsing that is required to copy the ELF segments in place, and the relocation processing that fixes up absolute symbol references to refer to the correct virtual addresses. Note that some of Evgeny's changes to clean up the PE/COFF header generation will still be needed, but I've omitted those here for brevity. Cc: Evgeniy Baskov <baskov@xxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Alexey Khoroshilov <khoroshilov@xxxxxxxxx> Cc: Peter Jones <pjones@xxxxxxxxxx> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> Cc: Dave Young <dyoung@xxxxxxxxxx> Cc: Mario Limonciello <mario.limonciello@xxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> [0] https://lore.kernel.org/all/cover.1678785672.git.baskov@xxxxxxxxx/ [1] https://lore.kernel.org/all/20230416120729.2470762-1-ardb@xxxxxxxxxx/ Ard Biesheuvel (6): x86: decompressor: Move global symbol references to C code x86: decompressor: Factor out kernel decompression and relocation x86: efistub: Obtain ACPI RSDP address while running in the stub x86: efistub: Perform 4/5 level paging switch from the stub x86: efistub: Prefer EFI memory attributes protocol over DXE services x86: efistub: Avoid legacy decompressor when doing EFI boot arch/x86/boot/compressed/efi_mixed.S | 55 --- arch/x86/boot/compressed/head_32.S | 24 -- arch/x86/boot/compressed/head_64.S | 39 +-- arch/x86/boot/compressed/misc.c | 44 ++- arch/x86/include/asm/efi.h | 2 + drivers/firmware/efi/libstub/efi-stub-helper.c | 4 + drivers/firmware/efi/libstub/x86-stub.c | 360 +++++++++++++------- 7 files changed, 279 insertions(+), 249 deletions(-) -- 2.39.2
