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

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Message-ID: <CALCETrXKteS9K=OOgsCvBU4in_3zcYccqF9hh2=OdCJPknvB8Q@mail.gmail.com>
Date:   Wed, 24 Feb 2021 11:30:34 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>, X86 ML <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>,
        "open list:DOCUMENTATION" <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>,
        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 11:20 AM Borislav Petkov <bp@...en8.de> wrote:
>
> 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.

I vote 0.  The address is in ucontext->gregs[REG_RIP] [0] regardless.
Why do we need to stick a copy somewhere else?

[0] or however it's spelled.  i can never remember.

>
> Thx.
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette