[PATCH 3/9] mm: Introduce VM_SHSTK for shadow stack memory

Yu-cheng Yu
2018-06-07T15:46:18Z

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@intel.com>
---
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 02a616e2f17d..bf4388a8cc41 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -221,11 +221,13 @@ 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 */

#if defined(CONFIG_X86)
@@ -257,6 +259,12 @@ 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 502d14189794..44c64711a309 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);
--
2.15.1