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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
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Sender: owner-linux-mm@kvack.org
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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

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