efi: implement generic compressed boot support

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, LoongArch and RISC-V. The latter was build tested only.

Changes since v4:
- make CONFIG_EFI_ZBOOT user selectable again, and turn it on by default only for LoongArch
- set KBUILD_IMAGE to vmlinuz.efi if CONFIG_EFI_ZBOOT=y, so that make targets such as zinstall and bindeb-pkg do the right thing
- throw an error is BSS was not cleared by the loader - this is needed to detect broken distro implementations of LoadImage in shim and grub
- add vmlinuz.* to .gitignore on the various architectures
- switch back to defining uncompressed_size as 'extern __aligned(1)' so that the compiler will perform the unaligned access as appropriate on the architecture in question - this requires the latest binutils on LoongArch [0]

Changes since v3:
- add support for XZ and ZSTD compression
- deal with exit data returned by StartImage()
- use LoadFile2 based image loading instead of passing the raw buffer - this way, the provenance of the data is more visible, allowing us, for instance, to deal with initrd= on arm64 transparently (this means that systemd-boot on arm64 will work unmodified provided that the [deprecated] command line initrd loader is enabled in the kernel build)
- include LoongArch support
- rename compressed image to vmlinuz.efi on all architectures

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.

[0] https://sourceware.org/pipermail/binutils/2022-September/122713.html

Ard Biesheuvel (8):
efi: name the ARCH-stub.c files uniformly
efi/libstub: add some missing EFI prototypes efi/libstub: use EFI provided memcpy/memset routines 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
loongarch: efi: enable generic EFI compressed boot

 arch/arm64/Makefile                                       |   9 +-
 arch/arm64/boot/.gitignore                                |   1 +
 arch/arm64/boot/Makefile                                  |   6 +
 arch/arm64/kernel/image-vars.h                            |  13 -
 arch/loongarch/Kconfig                                    |   1 +
 arch/loongarch/Makefile                                   |   4 +-
 arch/loongarch/boot/.gitignore                            |   1 +
 arch/loongarch/boot/Makefile                              |   6 +
 arch/loongarch/kernel/image-vars.h                        |   3 -
 arch/riscv/Makefile                                       |   6 +-
 arch/riscv/boot/.gitignore                                |   1 +
 arch/riscv/boot/Makefile                                  |   6 +
 arch/riscv/kernel/image-vars.h                            |   9 -
 drivers/firmware/efi/Kconfig                              |  38 +++
 drivers/firmware/efi/libstub/Makefile                     |  21 +-
 drivers/firmware/efi/libstub/Makefile.zboot               |  70 +++++
 drivers/firmware/efi/libstub/{arm32-stub.c => arm-stub.c} |   0
 drivers/firmware/efi/libstub/efi-stub.c                   |   2 -
 drivers/firmware/efi/libstub/efistub.h                    |  35 ++-
 drivers/firmware/efi/libstub/file.c                       |  17 ++
 drivers/firmware/efi/libstub/intrinsics.c                 |  30 ++
 drivers/firmware/efi/libstub/systable.c                   |   8 +
 drivers/firmware/efi/libstub/zboot-header.S               | 143 ++++++++++
 drivers/firmware/efi/libstub/zboot.c                      | 296 ++++++++++++++++++++
 drivers/firmware/efi/libstub/zboot.lds                    |  43 +++
 include/linux/efi.h                                       |  13 +
 26 files changed, 732 insertions(+), 50 deletions(-)
 create mode 100644 drivers/firmware/efi/libstub/Makefile.zboot
 rename drivers/firmware/efi/libstub/{arm32-stub.c => arm-stub.c} (100%)
 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