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References: <20180607143855.3681-1-yu-cheng.yu@intel.com> <20180607143855.3681-6-yu-cheng.yu@intel.com>
In-Reply-To: <20180607143855.3681-6-yu-cheng.yu@intel.com>
From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 7 Jun 2018 13:50:26 -0700
Message-ID: <CALCETrVRH8LeYoo7V1VBPqg4WS0Enxtizt=T7dPvgoeWfJrdzA@mail.gmail.com>
Subject: Re: [PATCH 5/7] x86: Insert endbr32/endbr64 to vDSO
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. J. Lu" <hjl.tools@gmail.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        mike.kravetz@oracle.com
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On Thu, Jun 7, 2018 at 7:42 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> From: "H.J. Lu" <hjl.tools@gmail.com>
>
> When Intel indirect branch tracking is enabled, functions in vDSO which
> may be called indirectly should have endbr32 or endbr64 as the first
> instruction.  We try to compile vDSO with -fcf-protection=branch -mibt
> if possible.  Otherwise, we insert endbr32 or endbr64 by hand to assembly
> codes generated by the compiler.

Wow, that's... a genuine abomination.  Do we really need to support
CET on kernels built with old toolchains?

--Andy