linux-kernel - Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection

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Message-ID: <CAMe9rOqhf4y+e6h8i7P8+70pwLSg8n=ise6LEqABNPKarECdeA@mail.gmail.com>
Date:   Wed, 26 Feb 2020 18:11:17 -0800
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for
 user-mode Shadow Stack protection

On Wed, Feb 26, 2020 at 5:16 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> 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.
>
> 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.

GCC 8 or above is needed since vDSO must be compiled with
--fcf-protection=branch.

> The point isn't to actually run CET at all.  The point is to get as many
> people as possible testing as much of it as possible.  Testing includes
> compile testing, static analysis and bloat watching.  It also includes
> functional and performance testing when you've got the feature compiled
> in but unavailable at runtime.  Did this hurt anything even when I'm not
> using it?
>

I will leave the CET toolchain issue to Yu-cheng.

-- 
H.J.