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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200918220355.GC7443@duo.ucw.cz>
Date:   Sat, 19 Sep 2020 00:03:55 +0200
From:   Pavel Machek <pavel@....cz>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        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 2020-09-18 14:46:12, H.J. Lu wrote:
> On Fri, Sep 18, 2020 at 2:40 PM Pavel Machek <pavel@....cz> wrote:
> >
> > On Fri 2020-09-18 14:25:12, Yu, Yu-cheng wrote:
> > > On 9/18/2020 1:59 PM, Pavel Machek 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@...el.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, ...." :-) ?
> > >
> > > I will revise the wording if there is another version.  But a CET-capable
> > > kernel can run on legacy systems.  We have been testing that combination.
> >
> > Yes, but enabling CET is unneccessary overhead on older systems. And
> > Kconfig is great place to explain that.
> >
> 
> I can't tell any visible CET kernel overhead on my non-CET machines.

I assume you are not a troll but you sound a bit like one.

Please list kernel size before and after enabling
X86_INTEL_CET option(s).

That's the overhead I'm talking about, and that's why Kconfig should
explain what machines this is useful on.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Download attachment "signature.asc" of type "application/pgp-signature" (196 bytes)