Update the x86 boot path to avoid the bare metal decompressor when booting via the EFI stub. The bare metal decompressor inherits the loader's 1:1 mapping of DRAM when entering in 64-bit mode, and assumes that all of it is mapped read/write/execute, which will no longer be the case on systems built to comply with recently tightened logo requirements (*). Changes since v3 [6]: - trivial rebase onto Kirill's unaccepted memory series v13 - test SNP feature mask while running in the EFI boot services, and fail gracefully on a mismatch - perform only the SEV init after ExitBootServices() Changes since v2 [4]: - update prose style to comply with -tip guidelines - rebased onto Kirill's unaccepted memory series [3] - add Kirill's ack to 4/5-level paging changes - perform SEV init and SNP feature check after ExitBootServices(), to avoid corrupting the firmware's own SEV state - split out preparatory refactor of handover entry code and BSS clearing (patches #1 to #4) Changes since v1 [2]: - streamline existing 4/5 level switching code and call it directly from the EFI stub - this is covered by the first 9 patches, which can be applied in isolation, if desired; - deal with SEV/SNP init explicitly; - clear BSS when booting via the 'handover protocol' - switch to kernel CS before calling SEV init code in kernel proper. ---- v1 cover letter follows ---- 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 allocation 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. (*) IMHO the following developments are likely to occur: - the Windows boot chain (along with 3rd party drivers) is cleaned up so that it never relies on memory being writable and executable at the same time when running under the EFI boot services; - the EFI reference implementation gets updated to map all memory NX by default, and to require read-only permissions for executable mappings; - BIOS vendors incorporate these changes into their codebases, and deploy it more widely than just the 'secure' SKUs; - OEMs only care about the Windows sticker [5], so they only boot test Windows, which works fine in this more restricted context; - Linux boot no longer works reliably on new hardware built for Windows unless we clean up our boot chain as well. 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> Cc: Joerg Roedel <jroedel@xxxxxxx> [0] https://lore.kernel.org/all/cover.1678785672.git.baskov@xxxxxxxxx/ [1] https://lore.kernel.org/all/20230416120729.2470762-1-ardb@xxxxxxxxxx/ [2] https://lore.kernel.org/all/20230424165726.2245548-1-ardb@xxxxxxxxxx/ [3] https://lore.kernel.org/all/20230518231434.26080-1-kirill.shutemov@xxxxxxxxxxxxxxx/ [4] https://lore.kernel.org/all/20230508070330.582131-1-ardb@xxxxxxxxxx/ [5] https://techcommunity.microsoft.com/t5/hardware-dev-center/new-uefi-ca-memory-mitigation-requirements-for-signing/ba-p/3608714 [6] https://lore.kernel.org/all/20230522071415.501717-1-ardb@xxxxxxxxxx/ Ard Biesheuvel (21): x86/efistub: Branch straight to kernel entry point from C code x86/efistub: Simplify and clean up handover entry code x86/decompressor: Avoid magic offsets for EFI handover entrypoint x86/efistub: Clear BSS in EFI handover protocol entrypoint x86/decompressor: Use proper sequence to take the address of the GOT x86/decompressor: Store boot_params pointer in callee save register x86/decompressor: Call trampoline as a normal function x86/decompressor: Use standard calling convention for trampoline x86/decompressor: Avoid the need for a stack in the 32-bit trampoline x86/decompressor: Call trampoline directly from C code x86/decompressor: Only call the trampoline when changing paging levels x86/decompressor: Merge trampoline cleanup with switching code x86/efistub: Perform 4/5 level paging switch from the stub x86/efistub: Prefer EFI memory attributes protocol over DXE services decompress: Use 8 byte alignment x86/decompressor: Move global symbol references to C code x86/decompressor: Factor out kernel decompression and relocation x86/head_64: Store boot_params pointer in callee-preserved register efi/libstub: Add limit argument to efi_random_alloc() x86/efistub: Perform SNP feature test while running in the firmware x86/efistub: Avoid legacy decompressor when doing EFI boot Documentation/arch/x86/boot.rst | 2 +- arch/x86/boot/compressed/Makefile | 5 + arch/x86/boot/compressed/efi_mixed.S | 107 +++----- arch/x86/boot/compressed/head_32.S | 34 +-- arch/x86/boot/compressed/head_64.S | 219 ++++----------- arch/x86/boot/compressed/misc.c | 44 +++- arch/x86/boot/compressed/pgtable.h | 6 +- arch/x86/boot/compressed/pgtable_64.c | 72 +++-- arch/x86/boot/compressed/sev.c | 74 ++++-- arch/x86/include/asm/boot.h | 8 + arch/x86/include/asm/efi.h | 7 +- arch/x86/include/asm/sev.h | 6 + arch/x86/kernel/head_64.S | 15 +- drivers/firmware/efi/libstub/Makefile | 1 + drivers/firmware/efi/libstub/arm64-stub.c | 2 +- drivers/firmware/efi/libstub/efi-stub-helper.c | 2 + drivers/firmware/efi/libstub/efistub.h | 3 +- drivers/firmware/efi/libstub/randomalloc.c | 10 +- drivers/firmware/efi/libstub/x86-5lvl.c | 94 +++++++ drivers/firmware/efi/libstub/x86-stub.c | 278 +++++++++++--------- drivers/firmware/efi/libstub/x86-stub.h | 17 ++ drivers/firmware/efi/libstub/zboot.c | 2 +- include/linux/decompress/mm.h | 2 +- 23 files changed, 511 insertions(+), 499 deletions(-) create mode 100644 drivers/firmware/efi/libstub/x86-5lvl.c create mode 100644 drivers/firmware/efi/libstub/x86-stub.h -- 2.39.2
