linux-kernel - Re: [PATCH 06/10] x86/cet: Add arch

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Date:   Thu, 7 Jun 2018 11:48:35 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        mike.kravetz@...cle.com
Subject: Re: [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack

On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>
> The following operations are provided.
>
> ARCH_CET_STATUS:
>         return the current CET status
>
> ARCH_CET_DISABLE:
>         disable CET features
>
> ARCH_CET_LOCK:
>         lock out CET features
>
> ARCH_CET_EXEC:
>         set CET features for exec()
>
> ARCH_CET_ALLOC_SHSTK:
>         allocate a new shadow stack
>
> ARCH_CET_PUSH_SHSTK:
>         put a return address on shadow stack
>
> ARCH_CET_ALLOC_SHSTK and ARCH_CET_PUSH_SHSTK are intended only for
> the implementation of GLIBC ucontext related APIs.

Please document exactly what these all do and why.  I don't understand
what purpose ARCH_CET_LOCK and ARCH_CET_EXEC serve.  CET is opt in for
each ELF program, so I think there should be no need for a magic
override.