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:

quoted

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>
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>
---
  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@kernel.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