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The existing approach of emitting this code into .head.text and checking for absolute relocations in that section is not 100% safe, and produces diagnostics that are sometimes difficult to interpret. [0] Instead, rely on symbol prefixes, similar to how this is implemented for the EFI stub and for the startup code in the arm64 port. This ensures that startup code can only call other startup code, unless a special symbol alias is emitted that exposes a non-startup routine to the startup code. This is somewhat intrusive, as there are many data objects that are referenced both by startup code and by ordinary code, and an alias needs to be emitted for each of those. If startup code references anything that has not been made available to it explicitly, a build time link error will occur. This ultimately allows the .head.text section to be dropped entirely, as it no longer has a special significance. Instead, code that only executes at boot is emitted into .init.text as it should. The majority of changes is around early SEV code. The main issue is that its use of GHCB pages and SVSM calling areas in code that may run from both the 1:1 mapping and the kernel virtual mapping is problematic as it relies on __pa() to perform VA to PA translations, which are ambiguous in this context. Also, __pa() pulls in non-trivial instrumented code when CONFIG_DEBUG_VIRTUAL=y and so it is better to avoid VA to PA translations altogether in the startup code. Changes since v4: - Incorporate feedback from Tom, and add a couple of RBs - Drop patch that moved the MSR save/restore out of the early page state change helper - this is less efficient but likely negligible in practice - Drop patch that unified the SEV-SNP hypervisor feature check, which was identified by Nikunj as the one breaking SEV-SNP boot. Changes since RFT/v3: - Rebase onto tip/master - Incorporate Borislav's feedback on v3 - Switch to objtool to check for absolute references in startup code - Remap inittext R-X when running on EFI implementations that require strict R-X/RW- separation - Include a kbuild fix to incorporate arch/x86/boot/startup/ in the right manner - For now, omit the LA57 changes that remove the problematic early 5-level paging checks. We can revisit this once there is agreement on the approach. Changes since RFT/v2: - Rebase onto tip/x86/boot and drop the patches from the previous revision that have been applied in the meantime. - Omit the pgtable_l5_enabled() changes for now, and just expose PIC aliases for the variables in question - this can be sorted later. - Don't use the boot SVSM calling area in snp_kexec_finish(), but pass down the correct per-CPU one to the early page state API. - Rename arch/x86/coco/sev/sev-noinstr.o to arch/x86/coco/sev/noinstr.o - Further reduce the amount of SEV code that needs to be constructed in a special way. Change since RFC/v1: - Include a major disentanglement/refactor of the SEV-SNP startup code, so that only code that really needs to run from the 1:1 mapping is included in the startup/ code - Incorporate some early notes from Ingo Cc: Borislav Petkov Cc: Ingo Molnar Cc: Kevin Loughlin Cc: Tom Lendacky Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: Nikunj A Dadhania [0] https://lore.kernel.org/all/CAHk-=wj7k9nvJn6cpa3-5Ciwn2RGyE605BMkjWE4MqnvC9E92A@mail.gmail.com/ Ard Biesheuvel (22): x86/sev: Separate MSR and GHCB based snp_cpuid() via a callback x86/sev: Use MSR protocol for remapping SVSM calling area x86/sev: Use MSR protocol only for early SVSM PVALIDATE call x86/sev: Run RMPADJUST on SVSM calling area page to test VMPL x86/sev: Move GHCB page based HV communication out of startup code x86/sev: Avoid global variable to store virtual address of SVSM area x86/sev: Share implementation of MSR-based page state change x86/sev: Pass SVSM calling area down to early page state change API x86/sev: Use boot SVSM CA for all startup and init code x86/boot: Drop redundant RMPADJUST in SEV SVSM presence check x86/boot: Provide PIC aliases for 5-level paging related constants x86/sev: Provide PIC aliases for SEV related data objects x86/sev: Move __sev_[get|put]_ghcb() into separate noinstr object x86/sev: Export startup routines for later use objtool: Add action to check for absence of absolute relocations x86/boot: Check startup code for absence of absolute relocations x86/boot: Revert "Reject absolute references in .head.text" x86/kbuild: Incorporate boot/startup/ via Kbuild makefile x86/boot: Create a confined code area for startup code efistub/x86: Remap inittext read-execute when needed x86/boot: Move startup code out of __head section x86/boot: Get rid of the .head.text section arch/x86/Kbuild | 2 + arch/x86/Makefile | 1 - arch/x86/boot/compressed/Makefile | 2 +- arch/x86/boot/compressed/misc.c | 2 + arch/x86/boot/compressed/sev-handle-vc.c | 3 + arch/x86/boot/compressed/sev.c | 108 +------ arch/x86/boot/startup/Makefile | 22 ++ arch/x86/boot/startup/exports.h | 14 + arch/x86/boot/startup/gdt_idt.c | 4 +- arch/x86/boot/startup/map_kernel.c | 4 +- arch/x86/boot/startup/sev-shared.c | 317 ++++++-------------- arch/x86/boot/startup/sev-startup.c | 196 ++---------- arch/x86/boot/startup/sme.c | 27 +- arch/x86/coco/sev/Makefile | 6 +- arch/x86/coco/sev/core.c | 169 ++++++++--- arch/x86/coco/sev/{sev-nmi.c => noinstr.c} | 74 +++++ arch/x86/coco/sev/vc-handle.c | 2 + arch/x86/coco/sev/vc-shared.c | 143 ++++++++- arch/x86/include/asm/boot.h | 2 + arch/x86/include/asm/init.h | 6 - arch/x86/include/asm/setup.h | 1 + arch/x86/include/asm/sev-internal.h | 27 +- arch/x86/include/asm/sev.h | 17 +- arch/x86/kernel/head64.c | 5 +- arch/x86/kernel/head_32.S | 2 +- arch/x86/kernel/head_64.S | 10 +- arch/x86/kernel/vmlinux.lds.S | 9 +- arch/x86/mm/mem_encrypt_amd.c | 6 - arch/x86/mm/mem_encrypt_boot.S | 6 +- arch/x86/platform/pvh/head.S | 2 +- arch/x86/tools/relocs.c | 8 +- drivers/firmware/efi/libstub/x86-stub.c | 4 +- tools/objtool/builtin-check.c | 2 + tools/objtool/check.c | 39 ++- tools/objtool/include/objtool/builtin.h | 1 + 35 files changed, 620 insertions(+), 623 deletions(-) create mode 100644 arch/x86/boot/startup/exports.h rename arch/x86/coco/sev/{sev-nmi.c => noinstr.c} (61%) -- 2.50.0.727.gbf7dc18ff4-goog