Re: [PATCH v23 9/9] x86/vdso: Add ENDBR to __vdso_sgx_enter_enclave

[Jarkko Sakkinen]

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@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

/Jarkko