[PATCH 08/12] x86, pkeys: arch-specific protection bits

[Dave Hansen <dave@sr71.net>]

Lots of things seem to do:

        vma->vm_page_prot = vm_get_page_prot(flags);

and the ptes get created right from things we pull out
of ->vm_page_prot.  So it is very convenient if we can
store the protection key in flags and vm_page_prot, just
like the existing permission bits (_PAGE_RW/PRESENT).  It
greatly reduces the amount of plumbing and arch-specific
hacking we have to do in generic code.

This also takes the new PROT_PKEY{0,1,2,3} flags and
turns *those* in to VM_ flags for vma->vm_flags.

The protection key values are stored in 4 places:
	1. "prot" argument to system calls
	2. vma->vm_flags, filled from the mmap "prot"
	3. vma->vm_page prot, filled from vma->vm_flags
	4. the PTE itself.

The pseudocode for these for steps are as follows:

	mmap(PROT_PKEY*)
	vma->vm_flags 	  = ... | arch_calc_vm_prot_bits(mmap_prot);
	vma->vm_page_prot = ... | arch_vm_get_page_prot(vma->vm_flags);
	pte = pfn | vma->vm_page_prot

Note that these are new definitions for x86:

	arch_vm_get_page_prot()
	arch_calc_vm_prot_bits()

---

 b/arch/x86/include/asm/pgtable_types.h |   12 ++++++++++--
 b/arch/x86/include/uapi/asm/mman.h     |   17 +++++++++++++++++
 b/include/linux/mm.h                   |    4 ++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff -puN arch/x86/include/asm/pgtable_types.h~pkeys-7-store-pkey-in-vma arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h~pkeys-7-store-pkey-in-vma	2015-05-07 10:31:43.740293543 -0700
+++ b/arch/x86/include/asm/pgtable_types.h	2015-05-07 10:31:43.747293858 -0700
@@ -104,7 +104,12 @@
 #define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |	\
 			 _PAGE_DIRTY)
 
-/* Set of bits not changed in pte_modify */
+/*
+ * Set of bits not changed in pte_modify.  The pte's
+ * protection key is treated like _PAGE_RW, for
+ * instance, and is *not* included in this mask since
+ * pte_modify() does modify it.
+ */
 #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
 			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
 			 _PAGE_SOFT_DIRTY)
@@ -220,7 +225,10 @@ enum page_cache_mode {
 /* PTE_PFN_MASK extracts the PFN from a (pte|pmd|pud|pgd)val_t */
 #define PTE_PFN_MASK		((pteval_t)PHYSICAL_PAGE_MASK)
 
-/* PTE_FLAGS_MASK extracts the flags from a (pte|pmd|pud|pgd)val_t */
+/*
+ *  PTE_FLAGS_MASK extracts the flags from a (pte|pmd|pud|pgd)val_t
+ *  This includes the protection key value.
+ */
 #define PTE_FLAGS_MASK		(~PTE_PFN_MASK)
 
 typedef struct pgprot { pgprotval_t pgprot; } pgprot_t;
diff -puN arch/x86/include/uapi/asm/mman.h~pkeys-7-store-pkey-in-vma arch/x86/include/uapi/asm/mman.h
--- a/arch/x86/include/uapi/asm/mman.h~pkeys-7-store-pkey-in-vma	2015-05-07 10:31:43.742293633 -0700
+++ b/arch/x86/include/uapi/asm/mman.h	2015-05-07 10:31:43.747293858 -0700
@@ -6,6 +6,23 @@
 #define MAP_HUGE_2MB    (21 << MAP_HUGE_SHIFT)
 #define MAP_HUGE_1GB    (30 << MAP_HUGE_SHIFT)
 
+/*
+ * Take the 4 protection key bits out of the vma->vm_flags
+ * value and turn them in to the bits that we can put in
+ * to a pte.
+ */
+#define arch_vm_get_page_prot(vm_flags)	__pgprot(	\
+		((vm_flags) & VM_PKEY_BIT0 ? _PAGE_PKEY_BIT0 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT1 ? _PAGE_PKEY_BIT1 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT2 ? _PAGE_PKEY_BIT2 : 0) |	\
+		((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0))
+
+#define arch_calc_vm_prot_bits(prot) (	\
+		((prot) & PROT_PKEY0 ? VM_PKEY_BIT0 : 0) |	\
+		((prot) & PROT_PKEY1 ? VM_PKEY_BIT1 : 0) |	\
+		((prot) & PROT_PKEY2 ? VM_PKEY_BIT2 : 0) |	\
+		((prot) & PROT_PKEY3 ? VM_PKEY_BIT3 : 0))
+
 #include <asm-generic/mman.h>
 
 #endif /* _ASM_X86_MMAN_H */
diff -puN include/linux/mm.h~pkeys-7-store-pkey-in-vma include/linux/mm.h
--- a/include/linux/mm.h~pkeys-7-store-pkey-in-vma	2015-05-07 10:31:43.744293723 -0700
+++ b/include/linux/mm.h	2015-05-07 10:31:43.748293904 -0700
@@ -162,6 +162,10 @@ extern unsigned int kobjsize(const void
 
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
+# define VM_PKEY_BIT0	VM_HIGH_ARCH_1	/* A protection key is a 4-bit value */
+# define VM_PKEY_BIT1	VM_HIGH_ARCH_2
+# define VM_PKEY_BIT2	VM_HIGH_ARCH_3
+# define VM_PKEY_BIT3	VM_HIGH_ARCH_4
 #elif defined(CONFIG_PPC)
 # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
 #elif defined(CONFIG_PARISC)
_