linux-kernel - Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled

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: <CAMe9rOqAmbRgGzUaA5ChGzeSqFVW524CJQ7Npe99BQtx-L_YBA@mail.gmail.com>
Date:   Fri, 18 Sep 2020 14:22:37 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Pavel Machek <pavel@....cz>, 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>,
        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>
Subject: Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled

On Fri, Sep 18, 2020 at 2:17 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 9/18/20 2:06 PM, H.J. Lu wrote:
> > On Fri, Sep 18, 2020 at 2:00 PM Pavel Machek <pavel@....cz> wrote:
> >> On Fri 2020-09-18 12:32:57, Dave Hansen wrote:
> >>> On 9/18/20 12:23 PM, Yu-cheng Yu wrote:
> >>>> Emulation of the legacy vsyscall page is required by some programs
> >>>> built before 2013.  Newer programs after 2013 don't use it.
> >>>> Disable vsyscall emulation when Control-flow Enforcement (CET) is
> >>>> enabled to enhance security.
> >>> How does this "enhance security"?
> >>>
> >>> What is the connection between vsyscall emulation and CET?
> >> Boom.
> >>
> >> We don't break compatibility by default, and you should not tell
> >> people to enable CET by default if you plan to do this.
> >>
> > Nothing will be broken.   CET enabled applications don't use/need
> > vsyscall emulation.
>
> Hi H.J.,
>
> Could you explain your logic a bit more thoroughly, please?

Here is my CET slides for LPC 2020:

https://gitlab.com/cet-software/cet-smoke-test/-/wikis/uploads/09431a51248858e6f716a59065d732e2/CET-LPC-2020.pdf

which may have answers for most questions.

> I also suspect that Pavel was confused by your changelog where you said
> that you do this when "CET is enabled".  Does enabled in this context mean:
> 1. Just CET support compiled in, or
> 2. Compiled in and on CET hardware, or
> 3. Compiled in to the kernel enabled in the app and running on CET
>    hardware?

CET is enabled only in a process if

1. All components are CET enabled, and
2. CPU supports CET, and
3. Kernel supports CET.

-- 
H.J.