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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Sat, 6 Mar 2021 13:25:36 +0100
Message-ID: <CACRpkdYrqy78EfB_+UY0QtA0v0tD+_+O09Pod8-1Vd-p-VyMWA@mail.gmail.com>
Subject: Re: [PATCH v5] ARM: Implement SLS mitigation
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>,
        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>,
        =?UTF-8?Q?Andreas_F=C3=A4rber?= <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
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On Fri, Mar 5, 2021 at 12:23 AM Jian Cai <jiancai@google.com> wrote:
> 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

And how does that work with this part of your patch:

+#define SLS_TEXT                                       \
+       ALIGN_FUNCTION();                              \
+       *(.text.__llvm_slsblr_thunk_*)

This does not look compiler agnostic?

Yours,
Linus Walleij