linux-kernel - Re: [RFC PATCH v2 25/27] x86/cet: Add PTRACE interface for CET

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Date:   Thu, 12 Jul 2018 15:37:14 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Ingo Molnar <mingo@...nel.org>
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@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.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@...omiun.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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v2 25/27] x86/cet: Add PTRACE interface for CET

On Thu, 2018-07-12 at 16:03 +0200, Ingo Molnar wrote:
> * Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
> 
> > 
> > > 
> > > > 
> > > > diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> > > > index e2ee403865eb..ac2bc3a18427 100644
> > > > --- a/arch/x86/kernel/ptrace.c
> > > > +++ b/arch/x86/kernel/ptrace.c
> > > > @@ -49,7 +49,9 @@ enum x86_regset {
> > > >  	REGSET_IOPERM64 = REGSET_XFP,
> > > >  	REGSET_XSTATE,
> > > >  	REGSET_TLS,
> > > > +	REGSET_CET64 = REGSET_TLS,
> > > >  	REGSET_IOPERM32,
> > > > +	REGSET_CET32,
> > > >  };
> > > Why does REGSET_CET64 alias on REGSET_TLS?
> > In x86_64_regsets[], there is no [REGSET_TLS].  The core dump code
> > cannot handle holes in the array.
> Is there a fundamental (ABI) reason for that?

What I did was, ran Linux with 'slub_debug', and forced a core dump
(kill -abrt <pid>), then there was a red zone warning in the dmesg.
My feeling is there could be issues in the core dump code.  These
enum's are only local to arch/x86/kernel/ptrace.c and not exported.
I am not aware this is in the ABI.

> 
> > 
> > > 
> > > to "CET" (which is a well-known acronym for "Central European Time"),
> > > not to CFE?
> > > 
> > I don't know if I can change that, will find out.
> So what I'd suggest is something pretty simple: to use CFT/cft in kernel internal 
> names, except for the Intel feature bit and any MSR enumeration which can be CET 
> if Intel named it that way, and a short comment explaining the acronym difference.
> 
> Or something like that.

Ok, I will make changes in the next version and probably revise
from that if still not optimal.

Yu-cheng