Hi Jian,
On Thu, Feb 11, 2021 at 09:14:58PM -0800, Jian Cai wrote:
> This patch adds a config CONFIG_HARDEN_SLS_ALL that can be used to turn
Drop "a config".
> on -mharden-sls=all, which mitigates the straight-line speculation
> vulnerability, or more commonly known as Spectre, Meldown.
^ I would drop "or" here
^ drop comma,
use "and",
typo: "Meltdown"
Although, is that a fair statement? SLS is not called Spectre or
Meltdown by ARM, it is a speculative processor vulnerabilty. It
might just be better to drop eerything after the first comma (although
maybe that is just being pedantic).
>
> 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.
I cannot comment on whether or not this is worth doing, I will leave
that up to Will, Catalin, et al. The following comments are more from a
"regular kernel developer" perspective, rather than an "arm64 kernel
developer" :)
> Link: https://reviews.llvm.org/D93221
> Link: https://reviews.llvm.org/D81404
> Link:
> https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
This is also a useful article it seems:
https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/frequently-asked-questions#SLS2
> Link: https://crbug.com/1171521
This crbug is private. If it is going into a commit message, please
publicize it.
> Suggested-by: Manoj Gupta <manojgu...@google.com>
> Signed-off-by: Jian Cai <jian...@google.com>
> ---
> arch/arm/Makefile | 4 ++++
> arch/arm64/Makefile | 5 +++++
> security/Kconfig.hardening | 11 +++++++++++
> 3 files changed, 20 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/arm64/Makefile b/arch/arm64/Makefile
> index 90309208bb28..8fd0ccd87eca 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -34,6 +34,11 @@ $(warning LSE atomics not supported by binutils)
> endif
> endif
>
> +ifeq ($(CONFIG_HARDEN_SLS_ALL), y)
> +KBUILD_CFLAGS += -mharden-sls=all
> +endif
> +
> +
Extra space here
> cc_has_k_constraint := $(call try-run,echo \
> 'int main(void) { \
> asm volatile("and w0, w0, %w0" :: "K" (4294967295)); \
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 269967c4fc1b..d83c406c81a3 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -121,6 +121,17 @@ choice
>
> endchoice
>
> +
> +config CC_HAS_HARDEN_SLS_ALL
> + def_bool $(cc-option,-mharden-sls=all)
I do not think that CONFIG_CC_HAS_HARDEN_SLS_ALL serves much purpose.
Moving the cc-option into CONFIG_HARDEN_SLS_ALL is just as clean.
config HARDEN_SLS_ALL
bool "enable SLS vulnerability hardening"
depends on $(cc-option,-mharden-sls=all)
help
Enables straight-line speculation vulnerability hardening
at highest level.
> +
> + config HARDEN_SLS_ALL
> + bool "enable SLS vulnerability hardening"
The spacing here seems messed up, I corrected it above.
> + depends on CC_HAS_HARDEN_SLS_ALL
> + help
> + Enables straight-line speculation vulnerability hardening
> + at highest level.
> +
> config GCC_PLUGIN_STRUCTLEAK_VERBOSE
> bool "Report forcefully initialized variables"
> depends on GCC_PLUGIN_STRUCTLEAK
> --
> 2.30.0.478.g8a0d178c01-goog
>
>
Cheers,
Nathan
