# Re: \[PATCH v27 10/10\] x86/vdso: Add ENDBR to \_\_vdso\_sgx\_enter\_enclave

- From: Yu, Yu-cheng \<hidden\>
- Date: 2021-05-24 19:01:57 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/05/1390432
- Thread: https://ratatoskr.run/linux-doc/2021/05/1388137/t.md

```text
On 5/22/2021 3:47 PM, Jarkko Sakkinen wrote:
> 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 <redacted>
>> Reviewed-by: Kees Cook <redacted>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Jarkko Sakkinen <jarkko@kernel.org>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>
>
> Acked-by: Jarkko Sakkinen <jarkko@kernel.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
>

Thanks!
```