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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v18 02/25] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection
Date:   Fri, 29 Jan 2021 11:58:21 -0800
Message-Id: <86F8CE62-A94B-46BD-9A29-DBE1CC14AA83@amacapital.net>
References: <40a5a9b5-9c83-473d-5f62-a16ecde50f2a@intel.com>
Cc:     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>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>
In-Reply-To: <40a5a9b5-9c83-473d-5f62-a16ecde50f2a@intel.com>
To:     Dave Hansen <dave.hansen@intel.com>
Precedence: bulk


> On Jan 29, 2021, at 11:42 AM, Dave Hansen <dave.hansen@intel.com> wrote:
>=20
> =EF=BB=BFOn 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.
>=20
> 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/.
>=20
> Just say:
>=20
>    Control-flow protection is a set of hardware features which
>    place additional restrictions on indirect branches.  These help
>    mitigate ROP attacks.
>=20
> ... and add more in the IBT patches.
>=20
>> 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.
>=20
> Did any CPUs ever get released that have this?  If so, name them.  If
> not, time to change this to 2021, I think.

Zen 3 :)=