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Date:   Fri, 18 Sep 2020 23:00:26 +0200
From:   Pavel Machek <pavel@ucw.cz>
To:     Dave Hansen <dave.hansen@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>,
        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>
Subject: Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is
 enabled
Message-ID: <20200918210026.GC4304@duo.ucw.cz>
References: <20200918192312.25978-1-yu-cheng.yu@intel.com>
 <20200918192312.25978-9-yu-cheng.yu@intel.com>
 <f02b511d-1d48-6dea-d2e6-84d58e21e6cd@intel.com>
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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.
>=20
> How does this "enhance security"?
>=20
> 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.

Best regards,

									Pavel
--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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