[PATCH v27 09/10] x86/vdso/32: Add ENDBR to __kernel_vsyscall entry point

[Yu-cheng Yu]

From: "H.J. Lu" <hjl.tools@xxxxxxxxx>

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 that to __kernel_vsyscall entry point.

Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/entry/vdso/vdso32/system_call.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
index 6ddd7a937b3e..d321c2ded33a 100644
--- a/arch/x86/entry/vdso/vdso32/system_call.S
+++ b/arch/x86/entry/vdso/vdso32/system_call.S
@@ -7,6 +7,7 @@
 #include <asm/dwarf2.h>
 #include <asm/cpufeatures.h>
 #include <asm/alternative.h>
+#include <asm/vdso.h>
 
 	.text
 	.globl __kernel_vsyscall
@@ -14,6 +15,7 @@
 	ALIGN
 __kernel_vsyscall:
 	CFI_STARTPROC
+	ENDBR32
 	/*
 	 * Reshuffle regs so that all of any of the entry instructions
 	 * will preserve enough state.
-- 
2.21.0