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Date: Tue, 18 Feb 2020 20:19:56 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Sami Tolvanen <samitolvanen@...gle.com>, 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@....com
Cc: 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@...glegroups.com, kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 01/12] add support for Clang's Shadow Call Stack (SCS)
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
> + be able to locate them and hijack control flow by modifying shadow
> + stacks that are not currently in use.
> +
> +config SHADOW_CALL_STACK_VMAP
> + bool "Use virtually mapped shadow call stacks"
> + depends on SHADOW_CALL_STACK
> + help
> + Use virtually mapped shadow call stacks. Selecting this option
> + provides better stack exhaustion protection, but increases per-thread
> + memory consumption as a full page is allocated for each shadow stack.
> +
> +
> config HAVE_ARCH_WITHIN_STACK_FRAMES
> bool
> help
thanks.
--
~Randy
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