linux-kernel - Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking

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Date:   Fri, 18 Sep 2020 14:36:11 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <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>,
        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>,
        Peter Zijlstra <peterz@...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>
Subject: Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode
 Indirect Branch Tracking

On Fri, Sep 18, 2020 at 2:24 PM Pavel Machek <pavel@....cz> wrote:
>
> Hi!
>
> > > > > +   help
> > > > > +     Indirect Branch Tracking (IBT) provides protection against
> > > > > +     CALL-/JMP-oriented programming attacks.  It is active when
> > > > > +     the kernel has this feature enabled, and the processor and
> > > > > +     the application support it.  When this feature is enabled,
> > > > > +     legacy non-IBT applications continue to work, but without
> > > > > +     IBT protection.
> > > > > +
> > > > > +     If unsure, say y
> > > >
> > > >         If unsure, say y.
> > >
> > > Actually, it would be "If unsure, say Y.", to be consistent with the
> > > rest of the Kconfig.
> > >
> > > But I wonder if Yes by default is good idea. Only very new CPUs will
> > > support this, right? Are they even available at the market? Should the
> > > help text say "if your CPU is Whatever Lake or newer, ...." :-) ?
> > >
> >
> > CET enabled kernel runs on all x86-64 processors.  All my machines
> > are running the same CET enabled kernel binary.
>
> I believe that.
>
> But enabling CET in kernel is useless on Core 2 Duo machine, right?
>

This is very important for CET kernel to run on Core 2 Duo machine.
Otherwise, a distro needs to provide 2 kernel binaries, one for CET
CPU and one for non-CET CPU.


-- 
H.J.