linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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

  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 " 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210223100453.GB10254@willie-the-truck \
    --to=will@kernel.org \
    --cc=David.Laight@aculab.com \
    --cc=afaerber@suse.de \
    --cc=akpm@linux-foundation.org \
    --cc=ardb@kernel.org \
    --cc=arnd@arndb.de \
    --cc=catalin.marinas@arm.com \
    --cc=clang-built-linux@googlegroups.com \
    --cc=dbrazdil@google.com \
    --cc=james.morse@arm.com \
    --cc=jiancai@google.com \
    --cc=jmorris@namei.org \
    --cc=keescook@chromium.org \
    --cc=linus.walleij@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=llozano@google.com \
    --cc=manojgupta@google.com \
    --cc=mark.rutland@arm.com \
    --cc=masahiroy@kernel.org \
    --cc=maz@kernel.org \
    --cc=mingo@kernel.org \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=rppt@kernel.org \
    --cc=serge@hallyn.com \
    --subject='Re: [PATCH v4] ARM: Implement SLS mitigation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox