linux-kernel - Re: [RFC PATCH v2 05/27] Documentation/x86: Add CET description

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Date:   Wed, 11 Jul 2018 08:25:49 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Pavel Machek <pavel@....cz>
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>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v2 05/27] Documentation/x86: Add CET description

On Wed, 2018-07-11 at 10:27 +0200, Pavel Machek wrote:
> On Tue 2018-07-10 15:26:17, Yu-cheng Yu wrote:
> > 
> > Explain how CET works and the no_cet_shstk/no_cet_ibt kernel
> > parameters.
> > 
> > 
> > --- /dev/null
> > +++ b/Documentation/x86/intel_cet.txt
> > @@ -0,0 +1,250 @@
> > +=========================================
> > +Control Flow Enforcement Technology (CET)
> > +=========================================
> We normally use .rst for this kind of formatted text.

I will change this to a .rst file.

> 
> 
> > 
> > +[6] The implementation of the SHSTK
> > +===================================
> > +
> > +SHSTK size
> > +----------
> > +
> > +A task's SHSTK is allocated from memory to a fixed size that can
> > +support 32 KB nested function calls; that is 256 KB for a 64-bit
> > +application and 128 KB for a 32-bit application.  The system admin
> > +can change the default size.
> How does admin change that? We already have ulimit for stack size,
> should those be somehow tied together?
> 
> $ ulimit -a
> ...
> stack size              (kbytes, -s) 8192
> 

We can do that.  This makes sense to me.

Yu-cheng