[RFC PATCH v2 00/21] KCFI support

Sami Tolvanen
2022-05-13T20:22:08Z

KCFI is a proposed forward-edge control-flow integrity scheme for
Clang, which is more suitable for kernel use than the existing CFI
scheme used by CONFIG_CFI_CLANG. KCFI doesn't require LTO, doesn't
alter function references to point to a jump table, and won't break
function address equality. The latest LLVM patch is here:

https://reviews.llvm.org/D119296

This RFC series replaces the current arm64 CFI implementation with
KCFI and adds support for x86_64.

KCFI requires assembly functions that are indirectly called from C
code to be annotated with type identifiers. As type information is
only available in C, the compiler emits expected type identifiers into
the symbol table, so they can be referenced from assembly without
having to hardcode type hashes. Patch 7 adds helper macros for
annotating functions, and patches 9 and 17 add annotations.

In case of a type mismatch, KCFI always traps. To support error
handling, the compiler generates a .kcfi_traps section for x86_64,
which contains the locations of each trap, and for arm64, encodes
the necessary register information to the ESR. Patches 10 and 20 add
arch-specific error handlers.

To test this series, you'll need to compile your own Clang toolchain
with the patches linked above. You can also find the complete source
tree here:

https://github.com/samitolvanen/llvm-project/commits/kcfi-rfc-v2

This series is also available in GitHub:

https://github.com/samitolvanen/linux/commits/kcfi-rfc-v2

Sami Tolvanen (21):
efi/libstub: Filter out CC_FLAGS_CFI
arm64/vdso: Filter out CC_FLAGS_CFI
kallsyms: Ignore __kcfi_typeid_
cfi: Remove CONFIG_CFI_CLANG_SHADOW
cfi: Drop __CFI_ADDRESSABLE
cfi: Switch to -fsanitize=kcfi
cfi: Add type helper macros
psci: Fix the function type for psci_initcall_t
arm64: Add types to indirect called assembly functions
arm64: Add CFI error handling
arm64: Drop unneeded __nocfi attributes
treewide: Drop function_nocfi
treewide: Drop WARN_ON_FUNCTION_MISMATCH
treewide: Drop __cficanonical
objtool: Don't warn about __cfi_ preambles falling through
x86/tools/relocs: Ignore __kcfi_typeid_ relocations
x86: Add types to indirectly called assembly functions
x86/purgatory: Disable CFI
x86/vdso: Disable CFI
x86: Add support for CONFIG_CFI_CLANG
init: Drop __nocfi from __init

Makefile | 13 +-
arch/Kconfig | 21 +-
arch/arm64/crypto/ghash-ce-core.S | 5 +-
arch/arm64/crypto/sm3-ce-core.S | 3 +-
arch/arm64/include/asm/brk-imm.h | 6 +
arch/arm64/include/asm/compiler.h | 16 -
arch/arm64/include/asm/ftrace.h | 2 +-
arch/arm64/include/asm/mmu_context.h | 4 +-
arch/arm64/kernel/acpi_parking_protocol.c | 2 +-
arch/arm64/kernel/alternative.c | 2 +-
arch/arm64/kernel/cpu-reset.S | 5 +-
arch/arm64/kernel/cpufeature.c | 4 +-
arch/arm64/kernel/ftrace.c | 2 +-
arch/arm64/kernel/machine_kexec.c | 2 +-
arch/arm64/kernel/psci.c | 2 +-
arch/arm64/kernel/smp_spin_table.c | 2 +-
arch/arm64/kernel/traps.c | 46 ++-
arch/arm64/kernel/vdso/Makefile | 3 +-
arch/arm64/mm/proc.S | 5 +-
arch/x86/Kconfig | 2 +
arch/x86/crypto/blowfish-x86_64-asm_64.S | 5 +-
arch/x86/entry/vdso/Makefile | 3 +-
arch/x86/include/asm/linkage.h | 12 +
arch/x86/kernel/traps.c | 60 +++-
arch/x86/lib/memcpy_64.S | 3 +-
arch/x86/purgatory/Makefile | 4 +
arch/x86/tools/relocs.c | 1 +
drivers/firmware/efi/libstub/Makefile | 2 +
drivers/firmware/psci/psci.c | 6 +-
drivers/misc/lkdtm/usercopy.c | 2 +-
include/asm-generic/bug.h | 16 -
include/asm-generic/vmlinux.lds.h | 37 +--
include/linux/cfi.h | 65 ++--
include/linux/cfi_types.h | 57 ++++
include/linux/compiler-clang.h | 6 +-
include/linux/compiler.h | 16 +-
include/linux/compiler_types.h | 4 -
include/linux/init.h | 6 +-
include/linux/module.h | 10 +-
include/linux/pci.h | 4 +-
kernel/cfi.c | 343 ++++------------------
kernel/kthread.c | 3 +-
kernel/module.c | 49 +---
kernel/workqueue.c | 2 +-
scripts/kallsyms.c | 1 +
scripts/module.lds.S | 23 +-
tools/objtool/check.c | 4 +
47 files changed, 357 insertions(+), 534 deletions(-)
create mode 100644 include/linux/cfi_types.h

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