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Subject: Re: [PATCH v30 01/32] Documentation/x86: Add CET description
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>,
        Rick P Edgecombe <rick.p.edgecombe@intel.com>
References: <20210830181528.1569-1-yu-cheng.yu@intel.com>
 <20210830181528.1569-2-yu-cheng.yu@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <e1f8debd-3097-a283-413a-1a54f79a579c@intel.com>
Date:   Tue, 5 Oct 2021 07:26:22 -0700
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On 8/30/21 11:14 AM, Yu-cheng Yu wrote:
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index bdb22006f713..3bc1a917dfef 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3319,6 +3319,13 @@
>  			noexec=on: enable non-executable mappings (default)
>  			noexec=off: disable non-executable mappings
>  
> +	no_user_shstk	[X86-64] Disable Shadow Stack for user-mode
> +			applications.  Disabling shadow stack also disables
> +			IBT.
> +
> +	no_user_ibt	[X86-64] Disable Indirect Branch Tracking for user-mode
> +			applications.
> +
>  	nosmap		[X86,PPC]
>  			Disable SMAP (Supervisor Mode Access Prevention)
>  			even if it is supported by processor.

Please add this documentation in the patch that *implements* the
command-line options.


> +++ b/Documentation/x86/intel_cet.rst
> @@ -0,0 +1,139 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================================
> +Control-flow Enforcement Technology (CET)
> +=========================================
> +
> +[1] Overview
> +============
> +
> +Control-flow Enforcement Technology (CET) is an Intel processor feature
> +that provides protection against return/jump-oriented programming (ROP)
> +attacks.  It can be set up to protect both applications and the kernel.
> +Only user-mode protection is implemented in the 64-bit kernel, including
> +shadow stack support for running legacy 32-bit applications.  IBT is not
> +supported for 32-bit applications.
> +
> +CET introduces Shadow Stack and Indirect Branch Tracking.
...

This is a *bit* confusing now.  AMD's manual describes shadow stacks,
but does not mention IBT.

We should probably consider whether "intel_cet.rst" is the best filename
for this.