[PATCH v2 0/9] kcfi: Prepare for GCC support

Kees Cook
2025-09-04T03:46:56Z

v2:
- integrate "transitional" Kconfig patch[2] (nathan, randy, miguel)
- add arm32 KCFI trap handler
- split pr_info changes (nathan)
- clean up my broken SoB (peter)
- remove Clang from CONFIG_CFI help (jeff)
- add r-b (linus)
v1: https://lore.kernel.org/all/20250825141316.work.967-kees@kernel.org/

Hi,

With KCFI support in GCC coming[1], we need to make some (relatively
small) changes in the kernel to deal with it:

- move __nocfi out of compilers-clang.h (so GCC can see it too)
- add cfi=debug so future Kees can find fineibt breakage easier
- remove problematic __noinitretpoline usage
- rename CONFIG_CFI_CLANG to CONFIG_CFI (otherwise it is quite confusing)

If I can get some Acks, I will carry this in the hardening tree, unless
someone else would like to take it (perhaps tip).

Thanks!

-Kees

[1] https://lore.kernel.org/linux-hardening/20250821064202.work.893-kees@kernel.org/
[2] https://lore.kernel.org/all/20250901182334.make.517-kees@kernel.org/

Kees Cook (9):
compiler_types.h: Move __nocfi out of compiler-specific header
x86/traps: Clarify KCFI instruction layout
x86/cfi: Document the "cfi=" bootparam options
x86/cfi: Standardize on common "CFI:" prefix for CFI reports
x86/cfi: Add "debug" option to "cfi=" bootparam
x86/cfi: Remove __noinitretpoline and __noretpoline
kconfig: Add transitional symbol attribute for migration support
kcfi: Rename CONFIG_CFI_CLANG to CONFIG_CFI
ARM: traps: Implement KCFI trap handler for ARM32

arch/Kconfig | 36 ++++---
arch/arm/Kconfig | 2 +-
arch/arm64/Kconfig | 4 +-
arch/riscv/Kconfig | 6 +-
arch/x86/Kconfig | 12 +--
init/Kconfig | 4 +-
kernel/module/Kconfig | 2 +-
.../kconfig/tests/err_transitional/Kconfig | 52 +++++++++
scripts/kconfig/tests/transitional/Kconfig | 100 +++++++++++++++++
lib/Kconfig.debug | 2 +-
Makefile | 2 +-
arch/arm/mm/Makefile | 2 +-
arch/riscv/kernel/Makefile | 2 +-
arch/riscv/purgatory/Makefile | 2 +-
arch/x86/kernel/Makefile | 2 +-
arch/x86/purgatory/Makefile | 2 +-
kernel/Makefile | 2 +-
scripts/kconfig/expr.h | 1 +
scripts/kconfig/lexer.l | 1 +
scripts/kconfig/parser.y | 47 ++++++++
scripts/kconfig/symbol.c | 16 ++-
.../tests/err_transitional/__init__.py | 14 +++
.../tests/err_transitional/expected_stderr | 7 ++
.../kconfig/tests/transitional/__init__.py | 18 ++++
.../tests/transitional/expected_config | 12 +++
.../kconfig/tests/transitional/initial_config | 16 +++
.../admin-guide/kernel-parameters.txt | 18 ++++
Documentation/kbuild/kconfig-language.rst | 32 ++++++
arch/riscv/include/asm/cfi.h | 4 +-
arch/x86/include/asm/cfi.h | 4 +-
include/asm-generic/vmlinux.lds.h | 2 +-
include/linux/cfi.h | 6 +-
include/linux/cfi_types.h | 8 +-
include/linux/compiler-clang.h | 5 -
include/linux/compiler-gcc.h | 4 -
include/linux/compiler.h | 2 +-
include/linux/compiler_types.h | 4 +-
include/linux/init.h | 8 --
tools/include/linux/cfi_types.h | 6 +-
tools/perf/util/include/linux/linkage.h | 2 +-
arch/arm/mm/cache-fa.S | 2 +-
arch/arm/mm/cache-v4.S | 2 +-
arch/arm/mm/cache-v4wb.S | 4 +-
arch/arm/mm/cache-v4wt.S | 2 +-
arch/arm/mm/cache-v6.S | 2 +-
arch/arm/mm/cache-v7.S | 2 +-
arch/arm/mm/cache-v7m.S | 2 +-
arch/arm/mm/proc-arm1020.S | 2 +-
arch/arm/mm/proc-arm1020e.S | 2 +-
arch/arm/mm/proc-arm1022.S | 2 +-
arch/arm/mm/proc-arm1026.S | 2 +-
arch/arm/mm/proc-arm920.S | 2 +-
arch/arm/mm/proc-arm922.S | 2 +-
arch/arm/mm/proc-arm925.S | 2 +-
arch/arm/mm/proc-arm926.S | 2 +-
arch/arm/mm/proc-arm940.S | 2 +-
arch/arm/mm/proc-arm946.S | 2 +-
arch/arm/mm/proc-feroceon.S | 2 +-
arch/arm/mm/proc-mohawk.S | 2 +-
arch/arm/mm/proc-xsc3.S | 2 +-
arch/arm/mm/tlb-v4.S | 2 +-
arch/arm/kernel/hw_breakpoint.c | 2 +-
arch/arm/kernel/traps.c | 102 ++++++++++++++++++
arch/arm64/kernel/debug-monitors.c | 2 +-
arch/arm64/kernel/traps.c | 4 +-
arch/arm64/kvm/handle_exit.c | 2 +-
arch/arm64/net/bpf_jit_comp.c | 2 +-
arch/riscv/net/bpf_jit_comp64.c | 4 +-
arch/x86/kernel/alternative.c | 44 ++++++--
arch/x86/kernel/cfi.c | 2 +-
arch/x86/kernel/kprobes/core.c | 2 +-
drivers/misc/lkdtm/cfi.c | 2 +-
kernel/module/tree_lookup.c | 2 +-
kernel/configs/hardening.config | 2 +-
74 files changed, 569 insertions(+), 118 deletions(-)
create mode 100644 scripts/kconfig/tests/err_transitional/Kconfig
create mode 100644 scripts/kconfig/tests/transitional/Kconfig
create mode 100644 scripts/kconfig/tests/err_transitional/__init__.py
create mode 100644 scripts/kconfig/tests/err_transitional/expected_stderr
create mode 100644 scripts/kconfig/tests/transitional/__init__.py
create mode 100644 scripts/kconfig/tests/transitional/expected_config
create mode 100644 scripts/kconfig/tests/transitional/initial_config

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2.34.1