linux-kernel - Re: [PATCH v23 9/9] x86/vdso: Add ENDBR to __vdso_sgx_enter

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Message-ID: <b523b794-3553-f7bb-3a69-24d936f0fefa@intel.com>
Date:   Tue, 16 Mar 2021 12:27:19 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     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>,
        Borislav Petkov <bp@...en8.de>,
        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>
Subject: Re: [PATCH v23 9/9] x86/vdso: Add ENDBR to __vdso_sgx_enter_enclave

On 3/16/2021 12:22 PM, Jarkko Sakkinen wrote:
> On Tue, Mar 16, 2021 at 08:13:19AM -0700, Yu-cheng Yu wrote:
>> 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 ENDBR to __vdso_sgx_enter_enclave() branch targets.
>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>> Cc: Jarkko Sakkinen <jarkko@...nel.org>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> ---
>>   arch/x86/entry/vdso/vsgx.S | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
>> index 86a0e94f68df..1baa9b49053e 100644
>> --- a/arch/x86/entry/vdso/vsgx.S
>> +++ b/arch/x86/entry/vdso/vsgx.S
>> @@ -6,6 +6,7 @@
>>   #include <asm/enclu.h>
>>   
>>   #include "extable.h"
>> +#include "../calling.h"
>>   
>>   /* Relative to %rbp. */
>>   #define SGX_ENCLAVE_OFFSET_OF_RUN		16
>> @@ -27,6 +28,7 @@
>>   SYM_FUNC_START(__vdso_sgx_enter_enclave)
>>   	/* Prolog */
>>   	.cfi_startproc
>> +	ENDBR
>>   	push	%rbp
>>   	.cfi_adjust_cfa_offset	8
>>   	.cfi_rel_offset		%rbp, 0
>> @@ -62,6 +64,7 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
>>   .Lasync_exit_pointer:
>>   .Lenclu_eenter_eresume:
>>   	enclu
>> +	ENDBR
>>   
>>   	/* EEXIT jumps here unless the enclave is doing something fancy. */
>>   	mov	SGX_ENCLAVE_OFFSET_OF_RUN(%rbp), %rbx
>> @@ -91,6 +94,7 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
>>   	jmp	.Lout
>>   
>>   .Lhandle_exception:
>> +	ENDBR
>>   	mov	SGX_ENCLAVE_OFFSET_OF_RUN(%rbp), %rbx
>>   
>>   	/* Set the exception info. */
>> -- 
>> 2.21.0
>>
>>
> 
> Looks good to me.
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

Thanks for reviewing.  In response to Dave's and Boris' comments, I will 
replace ENDBR macro with _CET_ENDBR that comes from the compiler.  Can I 
still keep the Reviewed-by?

> 
> /Jarkko
>