linux-kernel - Re: [PATCH v23 6/9] x86/entry: Introduce ENDBR macro

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Message-ID: <b0de1933-29ca-6c18-5a11-e293e9415f19@intel.com>
Date:   Tue, 16 Mar 2021 10:42:13 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.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>, Pavel Machek <pavel@....cz>,
        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>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Subject: Re: [PATCH v23 6/9] x86/entry: Introduce ENDBR macro

On 3/16/2021 10:30 AM, Borislav Petkov wrote:
> On Tue, Mar 16, 2021 at 10:12:39AM -0700, Yu, Yu-cheng wrote:
>> Alternatively, there is another compiler-defined macro _CET_ENDBR that can
>> be used.  We can put the following in calling.h:
> 
> Not calling.h - this is apparently needed in vdso code only so I guess
> some header there, arch/x86/include/asm/vdso.h maybe? In the
> 
> #else /* __ASSEMBLER__ */
> 
> branch maybe...
> 
>> #ifdef __CET__
>> #include <cet.h>
>> #else
>> #define _CET_ENDBR
>> #endif
>>
>> and then use _CET_ENDBR in other files.  How is that?
> 
> What does that macro do? Issue an ENDBR only?
> 

Yes, issue endbr32, endbr64, or nothing when cet is not enabled.