linux-kernel - Re: [PATCH v27 10/10] x86/vdso: Add ENDBR to __vdso_sgx_enter

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Date:   Sun, 23 May 2021 01:47:06 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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 v27 10/10] x86/vdso: Add ENDBR to __vdso_sgx_enter_enclave

On Fri, May 21, 2021 at 03:15:31PM -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>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 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>


Acked-by: Jarkko Sakkinen <jarkko@...nel.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 99dafac992e2..c7cb85d57b3f 100644
> --- a/arch/x86/entry/vdso/vsgx.S
> +++ b/arch/x86/entry/vdso/vsgx.S
> @@ -4,6 +4,7 @@
>  #include <asm/export.h>
>  #include <asm/errno.h>
>  #include <asm/enclu.h>
> +#include <asm/vdso.h>
>  
>  #include "extable.h"
>  
> @@ -27,6 +28,7 @@
>  SYM_FUNC_START(__vdso_sgx_enter_enclave)
>  	/* Prolog */
>  	.cfi_startproc
> +	ENDBR64
>  	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
> +	ENDBR64
>  
>  	/* 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:
> +	ENDBR64
>  	mov	SGX_ENCLAVE_OFFSET_OF_RUN(%rbp), %rbx
>  
>  	/* Set the exception info. */
> -- 
> 2.21.0
> 
> 

/Jarkko