linux-kernel - Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET

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Message-ID: <8fcde9bb-284f-f089-96d3-702f501a6258@intel.com>
Date:   Thu, 3 Sep 2020 09:42:28 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        Jann Horn <jannh@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        kernel list <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>,
        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>,
        "H.J. Lu" <hjl.tools@...il.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>
Subject: Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET

On 9/3/20 9:32 AM, Andy Lutomirski wrote:
>> Taking the config register out of the init state is illogical, as is
>> writing to SSP while the config register is in its init state.
> What's so special about the INIT state?  It's optimized by XSAVES, but
> it's just a number, right?  So taking the register out of the INIT
> state is kind of like saying "gdb wanted to set xmm0 to (0,0,0,1), but
> it was in the INIT state to begin with", right?

Yeah, that's a good point.  The init state shouldn't be special, as the
hardware is within its right to choose not to use the init optimization
at any time.