[RFC][PATCH 04/10] x86/espfix: use kernel-default PTE mask

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

In creating its page tables, the espfix code masks its PGTABLE_PROT
value with the supported mask: __supported_pte_mask.  This ensures
that unsupported bits are not set in the final PTE.  But, it also
sets _PAGE_GLOBAL which we do not want for PTE.  Use
__default_kernel_pte_mask instead which clears _PAGE_GLOBAL for PTI.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Nadav Amit <namit@xxxxxxxxxx>
---

 b/arch/x86/kernel/espfix_64.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported arch/x86/kernel/espfix_64.c
--- a/arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported	2018-02-22 12:36:19.217036552 -0800
+++ b/arch/x86/kernel/espfix_64.c	2018-02-22 12:36:19.221036552 -0800
@@ -167,7 +167,7 @@ void init_espfix_ap(int cpu)
 		goto unlock_done;
 
 	node = cpu_to_node(cpu);
-	ptemask = __supported_pte_mask;
+	ptemask = __default_kernel_pte_mask;
 
 	pud_p = &espfix_pud_page[pud_index(addr)];
 	pud = *pud_p;
_