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From: Nathan Chancellor <nathan@kernel.org>
To: Jian Cai <jiancai@google.com>
Cc: linux-kernel@vger.kernel.org, "Kees Cook" <keescook@chromium.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Daniel Palmer" <daniel@0x0f.com>,
	ndesaulniers@google.com, "Russell King" <linux@armlinux.org.uk>,
	clang-built-linux@googlegroups.com,
	linux-security-module@vger.kernel.org, manojgupta@google.com,
	"Andreas Färber" <afaerber@suse.de>,
	llozano@google.com, "James Morris" <jmorris@namei.org>,
	"Will Deacon" <will@kernel.org>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	"Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH] ARM: Implement Clang's SLS mitigation
Date: Thu, 11 Feb 2021 22:55:08 -0700	[thread overview]
Message-ID: <20210212055508.GA3822196@ubuntu-m3-large-x86> (raw)
In-Reply-To: <20210212051500.943179-1-jiancai@google.com>

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 <manojgupta@google.com>
> Signed-off-by: Jian Cai <jiancai@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

  reply	other threads:[~2021-02-12  5:56 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12  5:14 Jian Cai
2021-02-12  5:55 ` Nathan Chancellor [this message]
2021-02-12 10:41   ` David Laight
2021-02-12 19:52     ` [PATCH v2] " Jian Cai
2021-02-17  9:49       ` Will Deacon
2021-02-17 11:05         ` David Laight
2021-03-25 14:01         ` Linus Walleij
2021-02-17 18:20       ` Nick Desaulniers
2021-02-19 20:18       ` [PATCH v3] ARM: Implement " Jian Cai
2021-02-19 20:30         ` Nathan Chancellor
2021-02-19 23:08         ` [PATCH v4] " Jian Cai
2021-02-21 10:13           ` Russell King - ARM Linux admin
2021-02-22 11:58           ` Will Deacon
2021-02-22 21:50             ` Jian Cai
2021-02-23 10:04               ` Will Deacon
2021-03-03 15:18                 ` Linus Walleij
2021-03-03 15:29                   ` David Laight
2021-03-03 15:31                     ` Linus Walleij
2021-02-23  2:31           ` [PATCH v5] " Jian Cai
2021-02-23  2:35             ` Jian Cai
2021-03-03 15:04               ` Linus Walleij
2021-03-04 23:22                 ` Jian Cai
2021-03-06 12:25                   ` Linus Walleij
2021-03-10  4:43                     ` Jian Cai
2021-03-22 11:45                       ` Linus Walleij
2021-03-23 22:39                         ` Jian Cai
2021-03-05  0:53               ` [PATCH v6] " Jian Cai
2021-03-05  9:52                 ` Will Deacon
2021-03-06 12:27                   ` Linus Walleij

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