linux-kernel - Re: [PATCH v21 06/26] x86/cet: Add control-protection fault handler

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Message-ID: <20210224192044.GH20344@zn.tnic>
Date:   Wed, 24 Feb 2021 20:20:44 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v21 06/26] x86/cet: Add control-protection fault handler

On Wed, Feb 24, 2021 at 09:56:13AM -0800, Yu, Yu-cheng wrote:
> No.  Maybe I am doing too much.  The GP fault sets si_addr to zero, for
> example.  So maybe do the same here?

No, you're looking at this from the wrong angle. This is going to be
user-visible and the moment it gets upstream, it is cast in stone.

So the whole use case of what luserspace needs to do or is going to do
or wants to do on a SEGV_CPERR, needs to be described, agreed upon by
people etc before it goes out. And thus clarified whether the address
gets copied out or not.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette