[PATCH v27 10/10] x86/vdso: Add ENDBR to __vdso_sgx_enter_enclave

[Yu-cheng Yu]

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>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
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 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