This series is another part of my effort to reduce the level of knowledge on the part of the bootloader or firmware of internal per-architecture details regarding where/how the kernel is loaded and where its initrd and other context data are passed. Changes since v2: - add patch to correct the image size as reported in the PE/COFF header, which is slightly too small at the moment for images that happen to execute from the offset they were loaded at by UEFI, - add even more slack to the image size for mixed mode, which may now run startup_32() misaligned with respect to the minimum alignment as reported in the bootparams struct - check for long mode support in the 32-bit PE/COFF entrypoint, so we can fail gracefully instead of hang later on, - simplify handover to efi_pe_entry() from startup_32() Changes since v1: - add mixed mode wrappers for the EFI loaded_image protocol (#2) - expose Exit() boot service and invoke it on errors rather than doing and ordinary function return or entering a deadloop (#3) - move code into .text and r/o data into .rodata where appropriate, and disentangle the mixed mode boot path and the ordinary one (#4) - disable initrd load from file in mixed mode - reorder patches #4 and #5 ---- v1 blurb (cont'd) --- The x86 architecture has a so-called 'EFI handover protocol', which defines how the bootparams struct should be populated, and how it should be interpreted to figure out where to load the kernel, and at which offset in the binary the entrypoint is located. This scheme allows the initrd to be loaded beforehand, and allows 32-bit firmware to invoke a 64-bit kernel via a special entrypoint that manages the state transitions between the two execution modes. Due to this, x86 loaders currently do not rely on LoadImage and StartImage, and therefore, are forced to re-implement things like image authentication for secure boot and taking the measurements for measured boot in their open coded clones of these routines. My previous series on this topic [0][1] implements a generic way to load the initrd from any source supported by the loader without relying on something like a device tree or bootparams structure, and so native boot should not need the EFI handover protocol anymore after those change are merged. What remains is mixed mode boot, which also needs the EFI handover protocol regardless of whether an initrd is loaded or not. So let's get rid of that requirement, and take advantage of the fact that EDK2 based firmware does support LoadImage() for X64 binaries on IA32 firmware, which means we can rely on the secure boot and measured boot checks being performed by the firmware. The only thing we need to put on top is a way to discover the non-native entrypoint into the binary in a way that does not rely on x86 specific headers and data structures. So let's introduce a new .compat header in the PE/COFF metadata of the bzImage, and populate it with a <machine type, entrypoint> tuple, allowing a generic EFI loader to decide whether the entrypoint supports its native machine type, and invoke it as an ordinary EFI application entrypoint. Since we will not be passing a bootparams structure, we need to discover the base of the image (which contains the setup header) via the loaded image protocol before we can enter the kernel in 32-bit mode at startup_32() A loader implementation for OVMF can be found at [2]. Note that this loader code is fully generic, and permits mixed mode images to be launched from the UEFI shell or other generic components based on LoadImage/Startimage. It could be used without modifications if other architectures ever emerge that support kernels that can be invoked from a non-native (but cross-type supported) loader. [0] https://lore.kernel.org/linux-arm-kernel/20200206140352.6300-1-ardb@xxxxxxxxxx/ [1] https://lore.kernel.org/linux-efi/20200216141104.21477-1-ardb@xxxxxxxxxx/ [2] https://github.com/ardbiesheuvel/edk2/commits/linux-efi-generic Cc: hdegoede@xxxxxxxxxx Cc: nivedita@xxxxxxxxxxxx Cc: x86@xxxxxxxxxx Ard Biesheuvel (6): efi/x86: add headroom to decompressor BSS to account for setup block efi/x86: Drop redundant .bss section efi/libstub/x86: Make loaded_image protocol handling mixed mode safe efi/libstub/x86: Use Exit() boot service to exit the stub on errors efi/x86: Implement mixed mode boot without the handover protocol efi/x86: Add true mixed mode entry point into .compat section arch/x86/boot/Makefile | 2 +- arch/x86/boot/compressed/head_64.S | 59 ++++++++++++- arch/x86/boot/header.S | 25 +++--- arch/x86/boot/tools/build.c | 86 +++++++++++++------ arch/x86/include/asm/efi.h | 8 ++ .../firmware/efi/libstub/efi-stub-helper.c | 4 +- drivers/firmware/efi/libstub/efistub.h | 50 +++++++---- drivers/firmware/efi/libstub/x86-stub.c | 53 +++++++----- 8 files changed, 207 insertions(+), 80 deletions(-) -- 2.17.1
