x86/mm: Introduce "default" kernel PTE mask

The __PAGE_KERNEL_* page permissions are "raw".  They contain bits
that may or may not be supported on the current processor.  They need
to be filtered by a mask (currently __supported_pte_mask) to turn them
into a value that we can actually set in a PTE.

These __PAGE_KERNEL_* values all contain _PAGE_GLOBAL.  But, with PTI,
we want to be able to support _PAGE_GLOBAL (have the bit set in
__supported_pte_mask) but not have it appear in any of these masks by
default.

This patch creates a new mask, __default_kernel_pte_mask, and applies
it when creating all of the PAGE_KERNEL_* masks.  This makes
PAGE_KERNEL_* safe to use anywhere (they only contain supported bits).
It also ensures that PAGE_KERNEL_* contains _PAGE_GLOBAL on PTI=n
kernels but clears _PAGE_GLOBAL when PTI=y.

We also make __default_kernel_pte_mask a non-GPL exported symbol
because there are plenty of driver-available interfaces that take
PAGE_KERNEL_* permissions.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180406205506.030DB6B6@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 insertions, 13 deletions

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index acfe755562a6..1e5a40673953 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -196,19 +196,21 @@ enum page_cache_mode {
 #define __PAGE_KERNEL_NOENC	(__PAGE_KERNEL)
 #define __PAGE_KERNEL_NOENC_WP	(__PAGE_KERNEL_WP)
 
-#define PAGE_KERNEL		__pgprot(__PAGE_KERNEL | _PAGE_ENC)
-#define PAGE_KERNEL_NOENC	__pgprot(__PAGE_KERNEL)
-#define PAGE_KERNEL_RO		__pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
-#define PAGE_KERNEL_EXEC	__pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
-#define PAGE_KERNEL_EXEC_NOENC	__pgprot(__PAGE_KERNEL_EXEC)
-#define PAGE_KERNEL_RX		__pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
-#define PAGE_KERNEL_NOCACHE	__pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
-#define PAGE_KERNEL_LARGE	__pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
-#define PAGE_KERNEL_LARGE_EXEC	__pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
-#define PAGE_KERNEL_VVAR	__pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
-
-#define PAGE_KERNEL_IO		__pgprot(__PAGE_KERNEL_IO)
-#define PAGE_KERNEL_IO_NOCACHE	__pgprot(__PAGE_KERNEL_IO_NOCACHE)
+#define default_pgprot(x)	__pgprot((x) & __default_kernel_pte_mask)
+
+#define PAGE_KERNEL		default_pgprot(__PAGE_KERNEL | _PAGE_ENC)
+#define PAGE_KERNEL_NOENC	default_pgprot(__PAGE_KERNEL)
+#define PAGE_KERNEL_RO		default_pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC	default_pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC_NOENC	default_pgprot(__PAGE_KERNEL_EXEC)
+#define PAGE_KERNEL_RX		default_pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
+#define PAGE_KERNEL_NOCACHE	default_pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE	default_pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE_EXEC	default_pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_VVAR	default_pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+
+#define PAGE_KERNEL_IO		default_pgprot(__PAGE_KERNEL_IO)
+#define PAGE_KERNEL_IO_NOCACHE	default_pgprot(__PAGE_KERNEL_IO_NOCACHE)
 
 #endif	/* __ASSEMBLY__ */
 
@@ -483,6 +485,7 @@ static inline pgprot_t pgprot_large_2_4k(pgprot_t pgprot)
 typedef struct page *pgtable_t;
 
 extern pteval_t __supported_pte_mask;
+extern pteval_t __default_kernel_pte_mask;
 extern void set_nx(void);
 extern int nx_enabled;