x86/asm/entry/64: Use a define for an invalid segment selector

... instead of a naked number, for better readability.

Signed-off-by: Borislav Petkov <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Will Drewry <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: bp3tk0v

arch/x86/include/asm/segment.h

@@ -39,6 +39,8 @@
 /* ... GDT has it cleared */
 #define SEGMENT_GDT		0x0
 
+#define GDT_ENTRY_INVALID_SEG	0
+
 #ifdef CONFIG_X86_32
 /*
  * The layout of the per-CPU GDT under Linux:

arch/x86/kernel/cpu/common.c

@@ -1184,7 +1184,7 @@ void syscall_init(void)
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target);
 #else
 	wrmsrl(MSR_CSTAR, ignore_sysret);
-	wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0ULL);
+	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
 	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);
 #endif