linux-kernel - Re: [PATCH v4] ARM: Implement SLS mitigation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 3 Mar 2021 16:18:32 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Will Deacon <will@...nel.org>
Cc:     Jian Cai <jiancai@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Luis Lozano <llozano@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nathan Chancellor <nathan@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Ingo Molnar <mingo@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        James Morse <james.morse@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v4] ARM: Implement SLS mitigation

On Tue, Feb 23, 2021 at 11:05 AM Will Deacon <will@...nel.org> wrote:
> On Mon, Feb 22, 2021 at 01:50:06PM -0800, Jian Cai wrote:
> > 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.

I wrote some suggestions on follow-ups in my reply, and I can
help out doing some of the patches, I think.

Since ARM32 RET is mov pc, <>
git grep 'mov.*pc,' | wc -l gives 93 sites in arch/arm.
I suppose these need to come out:

mov pc, lr
dsb(nsh);
isb();

As ARM32 doesn't have sb my idea is to make a macro
"sb" that resolves to dsb/isb when this is enabled and then
we could start patching all the assembly users with that as
well. I need the Kconfig symbol from this patch though.

I also suggest selecting this mitigation as part of
HARDEN_BRANCH_PREDICTOR, by the token that either
you want all of them or none of them.

Yours,
Linus Walleij