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From: Jian Cai <jiancai@google.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: "Nick Desaulniers" <ndesaulniers@google.com>,
	"Manoj Gupta" <manojgupta@google.com>,
	"Luis Lozano" <llozano@google.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"David Laight" <David.Laight@aculab.com>,
	"Will Deacon" <will@kernel.org>,
	"Russell King" <rmk+kernel@armlinux.org.uk>,
	"Russell King" <linux@armlinux.org.uk>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"James Morris" <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Marc Zyngier" <maz@kernel.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Andreas Färber" <afaerber@suse.de>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"David Brazdil" <dbrazdil@google.com>,
	"James Morse" <james.morse@arm.com>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH v5] ARM: Implement SLS mitigation
Date: Thu, 4 Mar 2021 15:22:51 -0800	[thread overview]
Message-ID: <CA+SOCL+M5YfhygG=ogqvqp7y40v+32RiteGr=53THzwvdGugyA@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdYC3iDD23SESM0j2=f56kr6ByKeedDQvkGwXbUC0br0fw@mail.gmail.com>

On Wed, Mar 3, 2021 at 7:04 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Tue, Feb 23, 2021 at 3:36 AM Jian Cai <jiancai@google.com> 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.
>
> I heard about compiler protection for this, so nice to see it happening!
>
> Would you happen to know if there is any plan to do the same for GCC?
> I know you folks at Google like LLVM, but if you know let us know.

I think gcc also has these options.
https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html

>
> > +config HARDEN_SLS_ALL
> > +       bool "enable SLS vulnerability hardening"
>
> I would go in and also edit arch/arm/mm/Kconfig under:
> config HARDEN_BRANCH_PREDICTOR add
> select HARDEN_SLS_ALL
>
> Because if the user wants hardening for branch prediction
> in general then the user certainly wants this as well, if
> available. The help text for that option literally says:
>
>  "This config option will take CPU-specific actions to harden
>    the branch predictor against aliasing attacks and may rely on
>    specific instruction sequences or control bits being set by
>    the system firmware."
>
> Notice this only turns on for CPUs with CPU_SPECTRE
> defined which makes sense. Also it is default y which fulfils
> Will's request that it be turned on by default where
> applicable. Notably it will not be turned on for pre-v7 silicon
> which would be unhelpful as they don't suffer from
> these bugs.

Thanks for the suggestion. I will update the patch.

>
> Reading Kristofs compiler patch here:
> https://reviews.llvm.org/rG195f44278c4361a4a32377a98a1e3a15203d3647
>
> I take it that for affected CPUs we should also patch all assembly
> in the kernel containing a RET, BR or BLR with
> DSB SYS followed by ISB?
>
> I suppose we would also need to look for any mov PC, <>
> code...
>
> I guess we can invent a "SB" macro to mimic what Aarch64 is
> doing so the code is easy to read. (Thinking aloud.)
>
> Yours,
> Linus Walleij

  reply	other threads:[~2021-03-04 23:23 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12  5:14 [PATCH] ARM: Implement Clang's " Jian Cai
2021-02-12  5:55 ` Nathan Chancellor
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 [this message]
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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