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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Fri, 18 Sep 2020 14:08:06 -0700
Message-ID: <CAMe9rOo0+SBPtN7yb8_-h0dRAoOXkad8wi9d-EiWAfgFSedXjQ@mail.gmail.com>
Subject: Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode
 Indirect Branch Tracking
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <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>,
        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>,
        Peter Zijlstra <peterz@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>
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On Fri, Sep 18, 2020 at 1:59 PM Pavel Machek <pavel@ucw.cz> wrote:
>
> On Fri 2020-09-18 13:24:13, Randy Dunlap wrote:
> > Hi,
> >
> > If you do another version of this:
> >
> > On 9/18/20 12:23 PM, Yu-cheng Yu wrote:
> > > Introduce Kconfig option X86_INTEL_BRANCH_TRACKING_USER.
> > >
> > > 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.
> > >
> > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> > > ---
> > > v10:
> > > - Change build-time CET check to config depends on.
> > >
> > >  arch/x86/Kconfig | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > >
> > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > index 6b6dad011763..b047e0a8d1c2 100644
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -1963,6 +1963,22 @@ config X86_INTEL_SHADOW_STACK_USER
> > >
> > >       If unsure, say y.
> > >
> > > +config X86_INTEL_BRANCH_TRACKING_USER
> > > +   prompt "Intel Indirect Branch Tracking for user-mode"
> > > +   def_bool n
> > > +   depends on CPU_SUP_INTEL && X86_64
> > > +   depends on $(cc-option,-fcf-protection)
> > > +   select X86_INTEL_CET
> > > +   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.

-- 
H.J.