linux-kernel - Re: [PATCH v18 02/25] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection

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Date:   Fri, 29 Jan 2021 11:42:31 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>, 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@...nel.org>,
        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>, Jann Horn <jannh@...gle.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>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v18 02/25] x86/cet/shstk: Add Kconfig option for user-mode
 control-flow protection

On 1/27/21 1:25 PM, Yu-cheng Yu wrote:
> +	help
> +	  Control-flow protection is a hardware security hardening feature
> +	  that detects function-return address or jump target changes by
> +	  malicious code.

It's not really one feature.  I also think it's not worth talking about
shadow stacks or indirect branch tracking in *here*.  Leave that for
Documentation/.

Just say:

	Control-flow protection is a set of hardware features which
	place additional restrictions on indirect branches.  These help
	mitigate ROP attacks.

... and add more in the IBT patches.

>  Applications must be enabled to use it, and old
> +	  userspace does not get protection "for free".
> +	  Support for this feature is present on processors released in
> +	  2020 or later.  Enabling this feature increases kernel text size
> +	  by 3.7 KB.

Did any CPUs ever get released that have this?  If so, name them.  If
not, time to change this to 2021, I think.