Hi Jian,
On Fri, Feb 19, 2021 at 12:18:40PM -0800, 'Jian Cai' via Clang Built Linux
wrote:
> This patch adds CONFIG_HARDEN_SLS_ALL that can be used to turn on
> -mharden-sls=all, which mitigates the straight-line speculation
> vulnerability, speculative execution of the instruction following some
> unconditional jumps. Notice -mharden-sls= has other options as below,
> and this config turns on the strongest option.
>
> all: enable all mitigations against Straight Line Speculation that are
> implemented.
> none: disable all mitigations against Straight Line Speculation.
> retbr: enable the mitigation against Straight Line Speculation for RET and BR
> instructions.
> blr: enable the mitigation against Straight Line Speculation for BLR
> instructions.
>
> Links:
> https://reviews.llvm.org/D93221
> https://reviews.llvm.org/D81404
> https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
> https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/frequently-asked-questions#SLS2
>
> Suggested-by: Manoj Gupta <manojgu...@google.com>
> Suggested-by: Nick Desaulniers <ndesaulni...@google.com>
> Suggested-by: Nathan Chancellor <nat...@kernel.org>
> Suggested-by: David Laight <david.lai...@aculab.com>
> Suggested-by: Will Deacon <w...@kernel.org>
> Reviewed-by: Nathan Chancellor <nat...@kernel.org>
My review still stands but in the future, if you significantly change
how a patch is structured or works, please drop my tag and let me re-add
it.
One comment below.
> Signed-off-by: Jian Cai <jian...@google.com>
> ---
>
> Changes v2 -> v3:
> Modify linker scripts as Nick suggested to address boot failure
> (verified with qemu). Added more details in Kconfig.hardening
> description. Disable the config by default.
>
> arch/arm/Makefile | 4 ++++
> arch/arm/include/asm/vmlinux.lds.h | 4 ++++
> arch/arm/kernel/vmlinux.lds.S | 1 +
> arch/arm64/Makefile | 4 ++++
> arch/arm64/kernel/vmlinux.lds.S | 5 +++++
> security/Kconfig.hardening | 10 ++++++++++
> 6 files changed, 28 insertions(+)
>
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index 4aaec9599e8a..11d89ef32da9 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -48,6 +48,10 @@ CHECKFLAGS += -D__ARMEL__
> KBUILD_LDFLAGS += -EL
> endif
>
> +ifeq ($(CONFIG_HARDEN_SLS_ALL), y)
> +KBUILD_CFLAGS += -mharden-sls=all
> +endif
> +
> #
> # The Scalar Replacement of Aggregates (SRA) optimization pass in GCC 4.9 and
> # later may result in code being generated that handles signed short and
> signed
> diff --git a/arch/arm/include/asm/vmlinux.lds.h
> b/arch/arm/include/asm/vmlinux.lds.h
> index 4a91428c324d..c7f9717511ca 100644
> --- a/arch/arm/include/asm/vmlinux.lds.h
> +++ b/arch/arm/include/asm/vmlinux.lds.h
> @@ -145,3 +145,7 @@
> __edtcm_data = .; \
> } \
> . = __dtcm_start + SIZEOF(.data_dtcm);
> +
> +#define SLS_TEXT \
> + ALIGN_FUNCTION(); \
> + *(.text.__llvm_slsblr_thunk_*)
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index f7f4620d59c3..e71f2bc97bae 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -63,6 +63,7 @@ SECTIONS
> .text : { /* Real text segment */
> _stext = .; /* Text and read-only data */
> ARM_TEXT
> + SLS_TEXT
> }
>
> #ifdef CONFIG_DEBUG_ALIGN_RODATA
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 90309208bb28..ca7299b356a9 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -34,6 +34,10 @@ $(warning LSE atomics not supported by binutils)
> endif
> endif
>
> +ifeq ($(CONFIG_HARDEN_SLS_ALL), y)
> +KBUILD_CFLAGS += -mharden-sls=all
> +endif
> +
> cc_has_k_constraint := $(call try-run,echo \
> 'int main(void) { \
> asm volatile("and w0, w0, %w0" :: "K" (4294967295)); \
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 4c0b0c89ad59..f8912e42ffcd 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -93,6 +93,10 @@ jiffies = jiffies_64;
> #define TRAMP_TEXT
> #endif
>
> +#define SLS_TEXT \
> + ALIGN_FUNCTION(); \
> + *(.text.__llvm_slsblr_thunk_*)
> +
> /*
> * The size of the PE/COFF section that covers the kernel image, which
> * runs from _stext to _edata, must be a round multiple of the PE/COFF
> @@ -144,6 +148,7 @@ SECTIONS
> HIBERNATE_TEXT
> TRAMP_TEXT
> *(.fixup)
> + SLS_TEXT
> *(.gnu.warning)
> . = ALIGN(16);
> *(.got) /* Global offset table */
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 269967c4fc1b..e70f227019e1 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -121,6 +121,16 @@ choice
>
> endchoice
>
> +config HARDEN_SLS_ALL
> + bool "enable SLS vulnerability hardening"
> + default n
> + def_bool $(cc-option,-mharden-sls=all)
This is a much more convoluted way of writing:
depends on $(cc-option,-mharden-sls=all)
"default n" is the default and "def_bool" is short for:
bool
default <expr>
which is defeated by the "default n".
> + help
> + Enables straight-line speculation vulnerability hardening on ARM and
> ARM64
> + architectures. It inserts speculation barrier sequences (SB or DSB+ISB
> + depending on the target architecture) after RET and BR, and replacing
> + BLR with BL+BR sequence.
> +
> config GCC_PLUGIN_STRUCTLEAK_VERBOSE
> bool "Report forcefully initialized variables"
> depends on GCC_PLUGIN_STRUCTLEAK
> --
> 2.30.0.617.g56c4b15f3c-goog
>
