linux-kernel - Re: [PATCH v14 1/7] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking

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Message-ID: <20201012191511.GC14048@grain>
Date:   Mon, 12 Oct 2020 22:15:11 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        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 v14 1/7] x86/cet/ibt: Add Kconfig option for user-mode
 Indirect Branch Tracking

On Mon, Oct 12, 2020 at 08:45:24AM -0700, Yu-cheng Yu wrote:
...
> +	  the application support it.  When this feature is enabled,
> +	  legacy non-IBT applications continue to work, but without
> +	  IBT protection.
> +	  Support for this feature is only known to be present on
> +	  processors released in 2020 or later.  CET features are also
> +	  known to increase kernel text size by 3.7 KB.

It seems the last sentence is redundant - new features always bloat
the kernel code and precise size may differ depending on compiler
and options. Surely this can be patched on top.