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Date: Wed, 19 Feb 2020 09:25:43 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>, Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>,
Marc Zyngier <maz@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 01/12] add support for Clang's Shadow Call Stack (SCS)
On Tue, Feb 18, 2020 at 8:20 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> Hi Sami,
>
> a couple of minor tweaks:
>
> On 2/18/20 4:08 PM, Sami Tolvanen wrote:
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 98de654b79b3..66b34fd0df54 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -526,6 +526,40 @@ config STACKPROTECTOR_STRONG
> > about 20% of all kernel functions, which increases the kernel code
> > size by about 2%.
> >
> > +config ARCH_SUPPORTS_SHADOW_CALL_STACK
> > + bool
> > + help
> > + An architecture should select this if it supports Clang's Shadow
> > + Call Stack, has asm/scs.h, and implements runtime support for shadow
> > + stack switching.
> > +
> > +config SHADOW_CALL_STACK
> > + bool "Clang Shadow Call Stack"
> > + depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> > + help
> > + This option enables Clang's Shadow Call Stack, which uses a
> > + shadow stack to protect function return addresses from being
> > + overwritten by an attacker. More information can be found from
>
> found in
>
> > + Clang's documentation:
> > +
> > + https://clang.llvm.org/docs/ShadowCallStack.html
> > +
> > + Note that security guarantees in the kernel differ from the ones
> > + documented for user space. The kernel must store addresses of shadow
> > + stacks used by other tasks and interrupt handlers in memory, which
> > + means an attacker capable reading and writing arbitrary memory may
>
> capable of
Thanks, Randy! I'll fix these in the next version.
Sami
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