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From: Linus Walleij <linus.walleij@linaro.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>,
	"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: Mon, 22 Mar 2021 12:45:45 +0100	[thread overview]
Message-ID: <CACRpkdbF43_CjSFNu_4FUCEqOB8CebrpXJpkzeW8TnPpRELBtg@mail.gmail.com> (raw)
In-Reply-To: <CA+SOCLLo2MdxCH3gFONHsKdvmGGm2vZuML9QdQfWuX2--qFEOA@mail.gmail.com>

On Wed, Mar 10, 2021 at 5:43 AM Jian Cai <jiancai@google.com> wrote:
> On Sat, Mar 6, 2021 at 4:25 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> > 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:

> > > 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?
>
> You are right, GCC does generate different oraphan section names. I
> will address it in the next version of the patch. Also it seems only
> arm64 gcc supports -mharden-sls=* at this moment, arm32 gcc does not
> support it yet. I don't know if there is any plan to implement it for
> 32-bit gcc, but should we patch arm32 linker script preemptively,
> assuming the sections will be named with the same pattern like how
> clang does so the kernel would not fail to boot when the flag is
> implemented?

I think the best thing is to have something like this:
Implement a macro such as this in
include/linux/compiler-clang.h

#define SLS_TEXT_SECTION *(.text.__llvm_slsblr_thunk_*)

then the corresponding in include/linux/compiler-gcc.h
but here also add a

#define SLS_TEXT_SECTION #error "no compiler support"

if the compiler version does not have this.

I don't know the exact best approach sadly, as the patch
looks now it seems a bit fragile, I wonder if you get linker
warnings when this section is unused?

Yours,
Linus Walleij

  reply	other threads:[~2021-03-22 11:46 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
2021-03-06 12:25                   ` Linus Walleij
2021-03-10  4:43                     ` Jian Cai
2021-03-22 11:45                       ` Linus Walleij [this message]
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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