Re: [PATCH] cfi: rust: pass -Zpatchable-function-entry on all architectures

Matthew Maurer
2024-10-08T18:03:37Z

Reviewed-By: Matthew Maurer <mmaurer@google.com>

On Tue, Oct 8, 2024 at 10:37 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> The KCFI sanitizer stores the CFI tag of a function just before its
> machine code. However, the patchable-function-entry flag can be used to
> introduce additional nop instructions before the machine code, taking up
> the space that normally holds the CFI tag. In this case, a backwards
> offset is applied to the CFI tag to move them out of the way of the nop
> instructions. To ensure that C and Rust agree on the offset used by CFI
> tags, pass the -Zpatchable-function-entry to rustc whenever it is passed
> to the C compiler.
>
> The required rustc version is bumped to 1.81.0 to ensure that the
> -Zpatchable-function-entry flag is available when CFI is used.
>
> Fixes: ca627e636551 ("rust: cfi: add support for CFI_CLANG with Rust")
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Note that this fix uses rustc-option which has a pending fix:
> https://lore.kernel.org/all/20241008-rustc-option-bootstrap-v2-1-e6e155b8f9f3@google.com/
> ---
> arch/arm64/Makefile | 2 ++
> arch/loongarch/Makefile | 1 +
> arch/riscv/Makefile | 2 ++
> init/Kconfig | 2 +-
> 4 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 9efd3f37c2fd..d7ec0bb09fc4 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -143,9 +143,11 @@ CHECKFLAGS += -D__aarch64__
> ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS),y)
> KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> CC_FLAGS_FTRACE := -fpatchable-function-entry=4,2
> + KBUILD_RUSTFLAGS += $(call rustc-option,-Zpatchable-function-entry=4$(comma)2)
> else ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_ARGS),y)
> KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> CC_FLAGS_FTRACE := -fpatchable-function-entry=2
> + KBUILD_RUSTFLAGS += $(call rustc-option,-Zpatchable-function-entry=2)
> endif
>
> ifeq ($(CONFIG_KASAN_SW_TAGS), y)
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index ae3f80622f4c..f9cef31d1f0e 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -44,6 +44,7 @@ endif
> ifdef CONFIG_DYNAMIC_FTRACE
> KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> CC_FLAGS_FTRACE := -fpatchable-function-entry=2
> +KBUILD_RUSTFLAGS += $(call rustc-option,-Zpatchable-function-entry=2)
> endif
>
> ifdef CONFIG_64BIT
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index d469db9f46f4..65d4dcba309a 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -16,8 +16,10 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> ifeq ($(CONFIG_RISCV_ISA_C),y)
> CC_FLAGS_FTRACE := -fpatchable-function-entry=4
> + KBUILD_RUSTFLAGS += $(call rustc-option,-Zpatchable-function-entry=4)
> else
> CC_FLAGS_FTRACE := -fpatchable-function-entry=2
> + KBUILD_RUSTFLAGS += $(call rustc-option,-Zpatchable-function-entry=2)
> endif
> endif
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 530a382ee0fe..43434b681c3f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1946,7 +1946,7 @@ config RUST
> depends on !GCC_PLUGIN_RANDSTRUCT
> depends on !RANDSTRUCT
> depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
> - depends on !CFI_CLANG || RUSTC_VERSION >= 107900 && HAVE_CFI_ICALL_NORMALIZE_INTEGERS
> + depends on !CFI_CLANG || RUSTC_VERSION >= 108100 && HAVE_CFI_ICALL_NORMALIZE_INTEGERS
> select CFI_ICALL_NORMALIZE_INTEGERS if CFI_CLANG
> depends on !CALL_PADDING || RUSTC_VERSION >= 108100
> depends on !KASAN_SW_TAGS
>
> ---
> base-commit: 4a335f920bc78e51b1d7d216d11f2ecbb6dd949f
> change-id: 20241008-cfi-patchable-all-ddd6275eaf4f
>
> Best regards,
> --
> Alice Ryhl <aliceryhl@google.com>
>