Re: [PATCH v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave - Yu, Yu-cheng

From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
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, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@kernel.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	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>,
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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 v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave
Date: Wed, 10 Mar 2021 14:55:55 -0800	[thread overview]
Message-ID: <8b8efe44-b79f-ce29-ee28-066f88c93840@intel.com> (raw)
In-Reply-To: <YElKjT2v628tidE/@kernel.org>

On 3/10/2021 2:39 PM, Jarkko Sakkinen wrote:
> On Wed, Mar 10, 2021 at 02:05:19PM -0800, Yu-cheng Yu wrote:
>> When CET is enabled, __vdso_sgx_enter_enclave() needs an endbr64
>> in the beginning of the function.
> 
> OK.
> 
> What you should do is to explain what it does and why it's needed.
> 

The endbr marks a branch target.  Without the "no-track" prefix, if an 
indirect call/jmp reaches a non-endbr opcode, a control-protection fault 
is raised.  Usually endbr's are inserted by the compiler.  For assembly, 
these have to be put in manually.  I will add this in the commit log if 
there is another revision.  Thanks!

--
Yu-cheng

>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Jarkko Sakkinen <jarkko@kernel.org>
>> ---
>>   arch/x86/entry/vdso/vsgx.S | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
>> index 86a0e94f68df..a70d4d09f713 100644
>> --- a/arch/x86/entry/vdso/vsgx.S
>> +++ b/arch/x86/entry/vdso/vsgx.S
>> @@ -27,6 +27,9 @@
>>   SYM_FUNC_START(__vdso_sgx_enter_enclave)
>>   	/* Prolog */
>>   	.cfi_startproc
>> +#ifdef CONFIG_X86_CET
>> +	endbr64
>> +#endif
>>   	push	%rbp
>>   	.cfi_adjust_cfa_offset	8
>>   	.cfi_rel_offset		%rbp, 0
>> -- 
>> 2.21.0
>>
>>
> 
> /Jarkko
> 