Relatively modern architectures such as arm64 or RISC-V don't implement a self-decompressing kernel, and leave it up to the bootloader to decompress the compressed image before executing it. For bare metal boot, this policy makes sense, as a self-decompressing image essentially duplicates a lot of fiddly preparation work to create a 1:1 mapping and set up the C runtime, and to discover or infer where DRAM lives from device trees or other firmware tables. For EFI boot, the situation is a bit different: the EFI entrypoint is called with a 1:1 cached mapping covering all of DRAM already active, and with a stack, a heap, a memory map and boot services to load and start images. This means it is rather trivial to implement a self-decompressing wrapper for EFI boot in a generic manner, and reuse it across architectures that implement EFI boot. The only slight downside is that when UEFI secure boot is enabled, the generic LoadImage/StartImage only allow signed images to be loaded and started, and we would prefer to avoid the need to sign both the inner and outer PE/COFF images. However, the only truly generic and portable way to achieve this is to rely on LoadImage/StartImage as the EFI spec defines them, and avoid making assumptions about how things might work under the hood, and how we might circumvent that. This includes just loading the image into memory and jumping to the PE entry point: in the context of secure boot, measured boot and other hardening measures the firmware may take (such as disallowing mappings that are both writable and executable), using the firmware's image loading API is the only maintainable choice. For this reason, this version of the series includes support for signing the images using sbsign, if the signing key and cert are specified in Kconfig. The code is wired up for arm64 and RISC-V. The latter was build tested only. I also tested the code with the upcoming LoongArch EFI stub support, which built correctly (using binutils 2.39) but needs some additional work before it will run as expected. Changes since v2: - drop some of the refactoring work to make efi_printk() available in the decompressor, and just use fixed strings instead; - provide memcpy/memmove/memset based on the UEFI boot services, instead of having to specify for each architecture how to wire these up; - drop PI/DXE based signature check circumvention, and just sign the inner image instead, if needed; - add a header to the zimage binary that identifies it as a EFI zboot image, and describes the compression algorithm and where the payload lives in the image - this might be used by non-EFI loaders to locate and decompress the bare metal image, given that the EFI zboot one is not a hybrid like the one it encapsulates. Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx> Cc: Peter Jones <pjones@xxxxxxxxxx> Cc: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> Cc: Heinrich Schuchardt <heinrich.schuchardt@xxxxxxxxxxxxx> Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> Cc: Atish Patra <atishp@xxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Huacai Chen <chenhuacai@xxxxxxxxxxx> Cc: Lennart Poettering <lennart@xxxxxxxxxxxxxx> Cc: Jeremy Linton <jeremy.linton@xxxxxxx> Ard Biesheuvel (6): efi/libstub: use EFI provided memcpy/memset routines efi/libstub: add some missing boot service prototypes efi/libstub: move efi_system_table global var into separate object efi/libstub: implement generic EFI zboot arm64: efi: enable generic EFI compressed boot riscv: efi: enable generic EFI compressed boot arch/arm64/Makefile | 7 +- arch/arm64/boot/Makefile | 6 + arch/arm64/kernel/image-vars.h | 13 -- arch/riscv/Makefile | 5 + arch/riscv/boot/Makefile | 6 + arch/riscv/kernel/image-vars.h | 9 -- drivers/firmware/efi/Kconfig | 31 ++++- drivers/firmware/efi/libstub/Makefile | 11 +- drivers/firmware/efi/libstub/Makefile.zboot | 69 ++++++++++ drivers/firmware/efi/libstub/efi-stub.c | 2 - drivers/firmware/efi/libstub/efistub.h | 12 +- drivers/firmware/efi/libstub/intrinsics.c | 30 +++++ drivers/firmware/efi/libstub/systable.c | 8 ++ drivers/firmware/efi/libstub/zboot-header.S | 139 ++++++++++++++++++++ drivers/firmware/efi/libstub/zboot.c | 101 ++++++++++++++ drivers/firmware/efi/libstub/zboot.lds | 39 ++++++ 16 files changed, 453 insertions(+), 35 deletions(-) create mode 100644 drivers/firmware/efi/libstub/Makefile.zboot create mode 100644 drivers/firmware/efi/libstub/intrinsics.c create mode 100644 drivers/firmware/efi/libstub/systable.c create mode 100644 drivers/firmware/efi/libstub/zboot-header.S create mode 100644 drivers/firmware/efi/libstub/zboot.c create mode 100644 drivers/firmware/efi/libstub/zboot.lds -- 2.35.1
