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Subject: Re: [RFC 17/17] arm64: compile the kernel with ptrauth
 -msign-return-address
To:     Kristina Martsenko <kristina.martsenko@arm.com>,
        linux-arm-kernel@lists.infradead.org
Cc:     linux-arch@vger.kernel.org, Jacob Bramley <jacob.bramley@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Adam Wallis <awallis@codeaurora.org>,
        Will Deacon <will.deacon@arm.com>,
        kvmarm@lists.cs.columbia.edu,
        Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>,
        Amit Kachhap <Amit.Kachhap@arm.com>,
        Dave P Martin <Dave.Martin@arm.com>,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>
References: <20181005084754.20950-1-kristina.martsenko@arm.com>
 <20181005084754.20950-18-kristina.martsenko@arm.com>
From:   Vladimir Murzin <vladimir.murzin@arm.com>
Message-ID: <d0e36e1f-fa1a-f4ab-5a83-11e095801fef@arm.com>
Date:   Thu, 11 Oct 2018 15:23:05 +0100
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Hi Kristina,

On 05/10/18 09:47, Kristina Martsenko wrote:
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 106039d25e2f..dbcd43ea99d8 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -56,6 +56,10 @@ KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
>  KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
>  KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
>  
> +ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
> +KBUILD_CFLAGS	+= -msign-return-address=all
> +endif

Should not it be done via cc-option so old toolchains keep working [1]?

[1]
$ aarch64-linux-gnu-gcc --version
aarch64-linux-gnu-gcc (Linaro GCC 2014.11) 4.9.3 20141031 (prerelease)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ aarch64-linux-gnu-gcc -msign-return-address=all
aarch64-linux-gnu-gcc: error: unrecognized command line option '-msign-return-address=all'
...

Cheers
Vladimir