From: Dave Hansen <dave.han...@linux.intel.com>

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.

Signed-off-by: Dave Hansen <dave.han...@linux.intel.com>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Kees Cook <keesc...@google.com>
Cc: Hugh Dickins <hu...@google.com>
Cc: Juergen Gross <jgr...@suse.com>
Cc: x...@kernel.org
Cc: Nadav Amit <na...@vmware.com>
---

 b/arch/x86/include/asm/pgtable_types.h |   29 ++++++++++++++++-------------
 b/arch/x86/mm/init.c                   |    6 ++++++
 b/arch/x86/mm/init_32.c                |    7 ++++++-
 b/arch/x86/mm/init_64.c                |    4 ++++
 4 files changed, 32 insertions(+), 14 deletions(-)

diff -puN arch/x86/include/asm/pgtable_types.h~KERN-pgprot-default 
arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h~KERN-pgprot-default  2018-02-22 
12:36:18.608036554 -0800
+++ b/arch/x86/include/asm/pgtable_types.h      2018-02-22 12:36:18.617036554 
-0800
@@ -145,6 +145,7 @@ enum page_cache_mode {
        _PAGE_CACHE_MODE_WP = 5,
        _PAGE_CACHE_MODE_NUM = 8
 };
+extern unsigned long __default_kernel_pte_mask;
 #endif
 
 #define _PAGE_CACHE_MASK       (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)
@@ -197,20 +198,22 @@ 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_VSYSCALL   __pgprot(__PAGE_KERNEL_VSYSCALL | _PAGE_ENC)
-#define PAGE_KERNEL_VVAR       __pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+#define default_pgprot(x)      __pgprot((x) & __default_kernel_pte_mask)
 
-#define PAGE_KERNEL_IO         __pgprot(__PAGE_KERNEL_IO)
-#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+#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_VSYSCALL   default_pgprot(__PAGE_KERNEL_VSYSCALL | 
_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__ */
 
diff -puN arch/x86/mm/init_32.c~KERN-pgprot-default arch/x86/mm/init_32.c
--- a/arch/x86/mm/init_32.c~KERN-pgprot-default 2018-02-22 12:36:18.610036554 
-0800
+++ b/arch/x86/mm/init_32.c     2018-02-22 12:36:18.618036554 -0800
@@ -543,8 +543,13 @@ static void __init pagetable_init(void)
        permanent_kmaps_init(pgd_base);
 }
 
-pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL);
+#define DEFAULT_PTE_MASK ~(_PAGE_NX | _PAGE_GLOBAL)
+/* Bits supported by the hardware: */
+pteval_t __supported_pte_mask __read_mostly = DEFAULT_PTE_MASK;
+/* Bits allowed in normal kernel mappings: */
+pteval_t __default_kernel_pte_mask __read_mostly = DEFAULT_PTE_MASK;
 EXPORT_SYMBOL_GPL(__supported_pte_mask);
+EXPORT_SYMBOL_GPL(__default_kernel_pte_mask);
 
 /* user-defined highmem size */
 static unsigned int highmem_pages = -1;
diff -puN arch/x86/mm/init_64.c~KERN-pgprot-default arch/x86/mm/init_64.c
--- a/arch/x86/mm/init_64.c~KERN-pgprot-default 2018-02-22 12:36:18.612036554 
-0800
+++ b/arch/x86/mm/init_64.c     2018-02-22 12:36:18.618036554 -0800
@@ -65,8 +65,12 @@
  * around without checking the pgd every time.
  */
 
+/* Bits supported by the hardware: */
 pteval_t __supported_pte_mask __read_mostly = ~0;
+/* Bits allowed in normal kernel mappings: */
+pteval_t __default_kernel_pte_mask __read_mostly = ~0;
 EXPORT_SYMBOL_GPL(__supported_pte_mask);
+EXPORT_SYMBOL_GPL(__default_kernel_pte_mask);
 
 int force_personality32;
 
diff -puN arch/x86/mm/init.c~KERN-pgprot-default arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~KERN-pgprot-default    2018-02-22 12:36:18.614036554 
-0800
+++ b/arch/x86/mm/init.c        2018-02-22 12:36:18.619036554 -0800
@@ -190,6 +190,12 @@ static void __init probe_page_size_mask(
                enable_global_pages();
        }
 
+       /* By the default is everything supported: */
+       __default_kernel_pte_mask = __supported_pte_mask;
+       /* Except when with PTI where the kernel is mostly non-Global: */
+       if (cpu_feature_enabled(X86_FEATURE_PTI))
+               __default_kernel_pte_mask &= ~_PAGE_GLOBAL;
+
        /* Enable 1 GB linear kernel mappings if available: */
        if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {
                printk(KERN_INFO "Using GB pages for direct mapping\n");
_

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