From: Will Deacon <will@kernel.org>
To: Jian Cai <jiancai@google.com>
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>,
"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>,
"Kees Cook" <keescook@chromium.org>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Andreas Färber" <afaerber@suse.de>,
"Ingo Molnar" <mingo@kernel.org>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Marc Zyngier" <maz@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 Mailing List" <linux-kernel@vger.kernel.org>,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH v4] ARM: Implement SLS mitigation
Date: Tue, 23 Feb 2021 10:04:53 +0000 [thread overview]
Message-ID: <20210223100453.GB10254@willie-the-truck> (raw)
In-Reply-To: <CA+SOCLJVGJSn67VU24wPDdsOVeHhGe+KO5ekOCusano=bhn1Mg@mail.gmail.com>
On Mon, Feb 22, 2021 at 01:50:06PM -0800, Jian Cai wrote:
> Please see my comments inlined below.
>
> Thanks,
> Jian
>
> On Mon, Feb 22, 2021 at 3:58 AM Will Deacon <will@kernel.org> wrote:
> >
> > On Fri, Feb 19, 2021 at 03:08:13PM -0800, Jian Cai 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 <manojgupta@google.com>
> > > Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> > > Suggested-by: Nathan Chancellor <nathan@kernel.org>
> > > Suggested-by: David Laight <David.Laight@aculab.com>
> > > Suggested-by: Will Deacon <will@kernel.org>
> > > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > > Signed-off-by: Jian Cai <jiancai@google.com>
> > > ---
> >
> > Please can you reply to my previous questions?
> >
> > https://lore.kernel.org/linux-arm-kernel/20210217094859.GA3706@willie-the-truck/
> >
> > (apologies if you did, but I don't see them in the archive or my inbox)
>
> I should have clarified the suggested-by tag was in regard to the
> Kconfig text change. Regarding your earlier questions, please see my
> comments below.
>
> > So I think that either we enable this unconditionally, or we don't enable it
> > at all (and people can hack their CFLAGS themselves if they want to).
>
> Not sure if this answers your question but this config should provide
> a way for people to turn on the mitigation at their own risk.
I'm not sure I see the point; either it's needed or its not. I wonder if
there's a plan to fix this in future CPUs (another question for the Arm
folks).
> > It would be helpful for one of the Arm folks to chime in, as I'm yet to see any
> > evidence that this is actually exploitable. Is it any worse that Spectre-v1,
> > where we _don't_ have a compiler mitigation?
>
> > Finally, do we have to worry about our assembly code?
>
> I am not sure if there are any plans to protect assembly code and I
> will leave it to the Arm folks since they know a whole lot better. But
> even without that part, we should still have better protection,
> especially when overhead does not look too bad: I did some preliminary
> experiments on ChromeOS, code size of vmlinux increased 3%, and there
> were no noticeable changes to run-time performance of the benchmarks I
> used.
If the mitigation is required, I'm not sure I see a lot of point in only
doing a half-baked job of it. It feels a bit like a box-ticking exercise,
in which case any overhead is too much.
Will
next prev parent reply other threads:[~2021-02-23 10:06 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 5:14 [PATCH] ARM: Implement Clang's SLS mitigation 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 [this message]
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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