VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
stack). In case architecture doesn't implement shadow stack, it's VM_NONE
Introducing a helper `is_shadow_stack_vma` to determine shadow stack vma
or not.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 mm/gup.c |  2 +-
 mm/vma.h | 10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index a82890b46a36..8e6e14179f6c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1282,7 +1282,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 		    !writable_file_mapping_allowed(vma, gup_flags))
 			return -EFAULT;
 
-		if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {
+		if (!(vm_flags & VM_WRITE) || is_shadow_stack_vma(vm_flags)) {
 			if (!(gup_flags & FOLL_FORCE))
 				return -EFAULT;
 			/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
diff --git a/mm/vma.h b/mm/vma.h
index 819f994cf727..0f238dc37231 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -357,7 +357,7 @@ static inline struct vm_area_struct *vma_prev_limit(struct vma_iterator *vmi,
 }
 
 /*
- * These three helpers classifies VMAs for virtual memory accounting.
+ * These four helpers classifies VMAs for virtual memory accounting.
  */
 
 /*
@@ -368,6 +368,11 @@ static inline bool is_exec_mapping(vm_flags_t flags)
 	return (flags & (VM_EXEC | VM_WRITE | VM_STACK)) == VM_EXEC;
 }
 
+static inline bool is_shadow_stack_vma(vm_flags_t vm_flags)
+{
+	return !!(vm_flags & VM_SHADOW_STACK);
+}
+
 /*
  * Stack area (including shadow stacks)
  *
@@ -376,7 +381,7 @@ static inline bool is_exec_mapping(vm_flags_t flags)
  */
 static inline bool is_stack_mapping(vm_flags_t flags)
 {
-	return ((flags & VM_STACK) == VM_STACK) || (flags & VM_SHADOW_STACK);
+	return ((flags & VM_STACK) == VM_STACK) || is_shadow_stack_vma(flags);
 }
 
 /*
@@ -387,7 +392,6 @@ static inline bool is_data_mapping(vm_flags_t flags)
 	return (flags & (VM_WRITE | VM_SHARED | VM_STACK)) == VM_WRITE;
 }
 
-
 static inline void vma_iter_config(struct vma_iterator *vmi,
 		unsigned long index, unsigned long last)
 {

-- 
2.45.0

On Tue, Oct 08, 2024 at 03:36:44PM -0700, Deepak Gupta wrote:
> VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
> VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
> stack). In case architecture doesn't implement shadow stack, it's VM_NONE
> Introducing a helper `is_shadow_stack_vma` to determine shadow stack vma
> or not.

Not that it makes any difference but the arm64 eneded up defining
VM_SHADOW_STACK to VM_HIGH_ARCH_6.

> Signed-off-by: Deepak Gupta <debug@rivosinc.com>
> ---
>  mm/gup.c |  2 +-
>  mm/vma.h | 10 +++++++---
>  2 files changed, 8 insertions(+), 4 deletions(-)

There's another test of VM_SHADOW_STACK in mainline now, added by my
change df7e1286b1dc3d6c ("mm: care about shadow stack guard gap when
getting an unmapped area") - sorry, I should've remembered this change
from your series and pulled it into mine.

> @@ -387,7 +392,6 @@ static inline bool is_data_mapping(vm_flags_t flags)
>         return (flags & (VM_WRITE | VM_SHARED | VM_STACK)) == VM_WRITE;
>  }
> 
> -
>  static inline void vma_iter_config(struct vma_iterator *vmi,
>                 unsigned long index, unsigned long last)

Unrelated whitespace change.