[RFC PATCH v2 08/27] mm: Introduce VM_SHSTK for shadow stack memory

[Yu-cheng Yu]

VM_SHSTK indicates a shadow stack memory area.

A shadow stack PTE must be read-only and dirty.  For non shadow
stack, we use a spare bit of the 64-bit PTE for dirty.  The PTE
changes are in the next patch.

There is no more spare bit in the 32-bit PTE (except for PAE) and
the shadow stack is not implemented for the 32-bit kernel.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 include/linux/mm.h | 8 ++++++++
 mm/internal.h      | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a0fbb9ffe380..d7b338b41593 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -222,11 +222,13 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_5	37	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
 #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
 #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
 #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
 #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
+#define VM_HIGH_ARCH_5	BIT(VM_HIGH_ARCH_BIT_5)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
@@ -264,6 +266,12 @@ extern unsigned int kobjsize(const void *objp);
 # define VM_MPX		VM_NONE
 #endif
 
+#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+# define VM_SHSTK	VM_HIGH_ARCH_5
+#else
+# define VM_SHSTK	VM_NONE
+#endif
+
 #ifndef VM_GROWSUP
 # define VM_GROWSUP	VM_NONE
 #endif
diff --git a/mm/internal.h b/mm/internal.h
index 9e3654d70289..b09c29762d85 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -280,6 +280,14 @@ static inline bool is_data_mapping(vm_flags_t flags)
 	return (flags & (VM_WRITE | VM_SHARED | VM_STACK)) == VM_WRITE;
 }
 
+/*
+ * Shadow stack area
+ */
+static inline bool is_shstk_mapping(vm_flags_t flags)
+{
+	return (flags & VM_SHSTK);
+}
+
 /* mm/util.c */
 void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct rb_node *rb_parent);
-- 
2.17.1