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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection
Date:   Wed, 26 Feb 2020 19:57:01 -0800
Message-Id: <FF42D299-D7A4-4884-9E45-DBEB5853FE56@amacapital.net>
References: <CAMe9rOqhf4y+e6h8i7P8+70pwLSg8n=ise6LEqABNPKarECdeA@mail.gmail.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>, x86-patch-review@intel.com
In-Reply-To: <CAMe9rOqhf4y+e6h8i7P8+70pwLSg8n=ise6LEqABNPKarECdeA@mail.gmail.com>
To:     "H.J. Lu" <hjl.tools@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Feb 26, 2020, at 6:11 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>=20
> =EF=BB=BFOn Wed, Feb 26, 2020 at 5:16 PM Dave Hansen <dave.hansen@intel.co=
m> wrote:
>>=20
>> On 2/26/20 5:02 PM, H.J. Lu wrote:
>>>> That way everybody with old toolchains can still build the kernel (and
>>>> run/test code with your config option on, btw...).
>>> CET requires a complete new OS image from kernel, toolchain, run-time.
>>> CET enabled kernel without the rest of updated OS won't give you CET
>>> at all.
>>=20
>> If you require a new toolchain, nobody even builds your fancy feature.
>> Probably including 0day and all of the lazy maintainers with crufty old
>> distros.
>=20
> GCC 8 or above is needed since vDSO must be compiled with
> --fcf-protection=3Dbranch.

Fair enough. I don=E2=80=99t particularly want to carry a gross hack to add t=
he ENDBRANCHes without compiler support.