[RFC PATCH v3 03/11] mseal: add can_modify_mm and can_modify_vma

[jeffxu@chromium.org]

From: Jeff Xu <jeffxu@chromium.org>

Two utilities to be used later.

can_modify_mm:
 checks sealing flags for given memory range.

can_modify_vma:
  checks sealing flags for given vma.

Signed-off-by: Jeff Xu <jeffxu@chromium.org>
---
 include/linux/mm.h | 18 ++++++++++++++++++
 mm/mseal.c         | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3d1120570de5..2435acc1f44f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3339,6 +3339,12 @@ static inline unsigned long vma_seals(struct vm_area_struct *vma)
 	return (vma->vm_seals & MM_SEAL_ALL);
 }
 
+extern bool can_modify_mm(struct mm_struct *mm, unsigned long start,
+		unsigned long end, unsigned long checkSeals);
+
+extern bool can_modify_vma(struct vm_area_struct *vma,
+		unsigned long checkSeals);
+
 #else
 static inline bool check_vma_seals_mergeable(unsigned long vm_seals1)
 {
@@ -3349,6 +3355,18 @@ static inline unsigned long vma_seals(struct vm_area_struct *vma)
 {
 	return 0;
 }
+
+static inline bool can_modify_mm(struct mm_struct *mm, unsigned long start,
+		unsigned long end, unsigned long checkSeals)
+{
+	return true;
+}
+
+static inline bool can_modify_vma(struct vm_area_struct *vma,
+		unsigned long checkSeals)
+{
+	return true;
+}
 #endif
 
 /* These take the mm semaphore themselves */
diff --git a/mm/mseal.c b/mm/mseal.c
index 13bbe9ef5883..d12aa628ebdc 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -26,6 +26,44 @@ static bool can_do_mseal(unsigned long types, unsigned long flags)
 	return true;
 }
 
+/*
+ * check if a vma is sealed for modification.
+ * return true, if modification is allowed.
+ */
+bool can_modify_vma(struct vm_area_struct *vma,
+		    unsigned long checkSeals)
+{
+	if (checkSeals & vma_seals(vma))
+		return false;
+
+	return true;
+}
+
+/*
+ * Check if the vmas of a memory range are allowed to be modified.
+ * the memory ranger can have a gap (unallocated memory).
+ * return true, if it is allowed.
+ */
+bool can_modify_mm(struct mm_struct *mm, unsigned long start, unsigned long end,
+		   unsigned long checkSeals)
+{
+	struct vm_area_struct *vma;
+
+	VMA_ITERATOR(vmi, mm, start);
+
+	if (!checkSeals)
+		return true;
+
+	/* going through each vma to check. */
+	for_each_vma_range(vmi, vma, end) {
+		if (!can_modify_vma(vma, checkSeals))
+			return false;
+	}
+
+	/* Allow by default. */
+	return true;
+}
+
 /*
  * Check if a seal type can be added to VMA.
  */
-- 
2.43.0.472.g3155946c3a-goog