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Date:   Wed, 28 Apr 2021 13:33:47 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
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        Arnd Bergmann <arnd@arndb.de>,
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        Balbir Singh <bsingharora@gmail.com>,
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        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>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
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        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>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v26 8/9] x86/vdso/32: Add ENDBR to __kernel_vsyscall
 entry point
Message-ID: <202104281333.C2F5433@keescook>
References: <20210427204720.25007-1-yu-cheng.yu@intel.com>
 <20210427204720.25007-9-yu-cheng.yu@intel.com>
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On Tue, Apr 27, 2021 at 01:47:19PM -0700, Yu-cheng Yu wrote:
> From: "H.J. Lu" <hjl.tools@gmail.com>
> 
> ENDBR is a special new instruction for the Indirect Branch Tracking (IBT)
> component of CET.  IBT prevents attacks by ensuring that (most) indirect
> branches and function calls may only land at ENDBR instructions.  Branches
> that don't follow the rules will result in control flow (#CF) exceptions.
> 
> ENDBR is a noop when IBT is unsupported or disabled.  Most ENDBR
> instructions are inserted automatically by the compiler, but branch
> targets written in assembly must have ENDBR added manually.
> 
> Add that to __kernel_vsyscall entry point.
> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook