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

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Message-Id: <20180222203658.80705136@viggo.jf.intel.com>
Date:   Thu, 22 Feb 2018 12:36:58 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>, aarcange@...hat.com,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, jgross@...e.com,
        x86@...nel.org, namit@...are.com
Subject: [RFC][PATCH 04/10] x86/espfix: use kernel-default PTE mask


From: Dave Hansen <dave.hansen@...ux.intel.com>

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@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: x86@...nel.org
Cc: Nadav Amit <namit@...are.com>
---

 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;
_