[PATCH v4 10/36] mm: Define VM_SHADOW_STACK for arm64 when we support GCS

[Mark Brown <broonie@kernel.org>]

Use VM_HIGH_ARCH_5 for guarded control stack pages.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 Documentation/filesystems/proc.rst |  2 +-
 fs/proc/task_mmu.c                 |  3 +++
 include/linux/mm.h                 | 12 +++++++++++-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 6ccb57089a06..086a0408a4d7 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -566,7 +566,7 @@ encoded manner. The codes are the following:
     mt    arm64 MTE allocation tags are enabled
     um    userfaultfd missing tracking
     uw    userfaultfd wr-protect tracking
-    ss    shadow stack page
+    ss    shadow/guarded control stack page
     ==    =======================================
 
 Note that there is no guarantee that every flag and associated mnemonic will
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index cfab855fe7e9..e8c50848bb16 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -711,6 +711,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
 #ifdef CONFIG_X86_USER_SHADOW_STACK
 		[ilog2(VM_SHADOW_STACK)] = "ss",
+#endif
+#ifdef CONFIG_ARM64_GCS
+		[ilog2(VM_SHADOW_STACK)] = "ss",
 #endif
 	};
 	size_t i;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 43fe625b85aa..3f939ae212e5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -372,7 +372,17 @@ extern unsigned int kobjsize(const void *objp);
  * having a PAGE_SIZE guard gap.
  */
 # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
-#else
+#endif
+
+#if defined(CONFIG_ARM64_GCS)
+/*
+ * arm64's Guarded Control Stack implements similar functionality and
+ * has similar constraints to shadow stacks.
+ */
+# define VM_SHADOW_STACK	VM_HIGH_ARCH_5
+#endif
+
+#ifndef VM_SHADOW_STACK
 # define VM_SHADOW_STACK	VM_NONE
 #endif
 

-- 
2.30.2