[PATCH 09/25] x86, pkeys: arch-specific protection bits

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

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 this provides a new definitions for x86:

	arch_vm_get_page_prot()

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---

 b/arch/x86/include/asm/mmu_context.h   |   20 ++++++++++++++++++++
 b/arch/x86/include/asm/pgtable_types.h |   12 ++++++++++--
 b/arch/x86/include/uapi/asm/mman.h     |   16 ++++++++++++++++
 b/include/linux/mm.h                   |    6 ++++++
 4 files changed, 52 insertions(+), 2 deletions(-)

diff -puN arch/x86/include/asm/mmu_context.h~pkeys-08-store-pkey-in-vma arch/x86/include/asm/mmu_context.h
--- a/arch/x86/include/asm/mmu_context.h~pkeys-08-store-pkey-in-vma	2015-09-28 11:39:44.957137779 -0700
+++ b/arch/x86/include/asm/mmu_context.h	2015-09-28 11:39:44.965138143 -0700
@@ -243,4 +243,24 @@ static inline void arch_unmap(struct mm_
 		mpx_notify_unmap(mm, vma, start, end);
 }
 
+static inline u16 vma_pkey(struct vm_area_struct *vma)
+{
+	u16 pkey = 0;
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+	unsigned long vma_pkey_mask = VM_PKEY_BIT0 | VM_PKEY_BIT1 |
+				      VM_PKEY_BIT2 | VM_PKEY_BIT3;
+	/*
+	 * ffs is one-based, not zero-based, so bias back down by 1.
+	 */
+	int vm_pkey_shift = __builtin_ffsl(vma_pkey_mask) - 1;
+	/*
+	 * gcc generates better code if we do this rather than:
+	 * pkey = (flags & mask) >> shift
+	 */
+	pkey = (vma->vm_flags >> vm_pkey_shift) &
+	       (vma_pkey_mask >> vm_pkey_shift);
+#endif
+	return pkey;
+}
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */
diff -puN arch/x86/include/asm/pgtable_types.h~pkeys-08-store-pkey-in-vma arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h~pkeys-08-store-pkey-in-vma	2015-09-28 11:39:44.959137870 -0700
+++ b/arch/x86/include/asm/pgtable_types.h	2015-09-28 11:39:44.965138143 -0700
@@ -111,7 +111,12 @@
 #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)
@@ -227,7 +232,10 @@ 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-08-store-pkey-in-vma arch/x86/include/uapi/asm/mman.h
--- a/arch/x86/include/uapi/asm/mman.h~pkeys-08-store-pkey-in-vma	2015-09-28 11:39:44.960137915 -0700
+++ b/arch/x86/include/uapi/asm/mman.h	2015-09-28 11:39:44.966138188 -0700
@@ -6,6 +6,22 @@
 #define MAP_HUGE_2MB    (21 << MAP_HUGE_SHIFT)
 #define MAP_HUGE_1GB    (30 << MAP_HUGE_SHIFT)
 
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+/*
+ * 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.
+ *
+ * Only override these if Protection Keys are available
+ * (which is only on 64-bit).
+ */
+#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))
+#endif
+
 #include <asm-generic/mman.h>
 
 #endif /* _ASM_X86_MMAN_H */
diff -puN include/linux/mm.h~pkeys-08-store-pkey-in-vma include/linux/mm.h
--- a/include/linux/mm.h~pkeys-08-store-pkey-in-vma	2015-09-28 11:39:44.962138006 -0700
+++ b/include/linux/mm.h	2015-09-28 11:39:44.967138234 -0700
@@ -166,6 +166,12 @@ extern unsigned int kobjsize(const void
 
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
+#if defined (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS)
+# define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 4-bit value */
+# define VM_PKEY_BIT1	VM_HIGH_ARCH_1
+# define VM_PKEY_BIT2	VM_HIGH_ARCH_2
+# define VM_PKEY_BIT3	VM_HIGH_ARCH_3
+#endif
 #elif defined(CONFIG_PPC)
 # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
 #elif defined(CONFIG_PARISC)
_
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