linux-hardening - [RFC PATCH v2 3/8] mseal: add can_modify_mm and can_modify

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Date: Tue, 17 Oct 2023 09:08:10 +0000
From: jeffxu@...omium.org
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Subject: [RFC PATCH v2 3/8] mseal: add can_modify_mm and can_modify_vma

From: Jeff Xu <jeffxu@...gle.com>

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@...gle.com>
---
 include/linux/mm.h | 26 ++++++++++++++++++++++++++
 mm/mseal.c         | 42 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b511932df033..b09df8501987 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3299,6 +3299,32 @@ static inline void mm_populate(unsigned long addr, unsigned long len)
 static inline void mm_populate(unsigned long addr, unsigned long len) {}
 #endif
 
+#ifdef CONFIG_MSEAL
+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);
+
+static inline unsigned long vma_seals(struct vm_area_struct *vma)
+{
+	return (vma->vm_seals & MM_SEAL_ALL);
+}
+
+#else
+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 */
 extern int __must_check vm_brk(unsigned long, unsigned long);
 extern int __must_check vm_brk_flags(unsigned long, unsigned long, unsigned long);
diff --git a/mm/mseal.c b/mm/mseal.c
index ffe4c4c3f1bc..3e9d1c732c38 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.
  */
@@ -33,7 +71,7 @@ static bool can_add_vma_seals(struct vm_area_struct *vma, unsigned long newSeals
 {
 	/* When SEAL_MSEAL is set, reject if a new type of seal is added */
 	if ((vma->vm_seals & MM_SEAL_MSEAL) &&
-	    (newSeals & ~(vma->vm_seals & MM_SEAL_ALL)))
+	    (newSeals & ~(vma_seals(vma))))
 		return false;
 
 	return true;
@@ -45,7 +83,7 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 {
 	int ret = 0;
 
-	if (addtypes & ~(vma->vm_seals & MM_SEAL_ALL)) {
+	if (addtypes & ~(vma_seals(vma))) {
 		/*
 		 * Handle split at start and end.
 		 * Note: sealed VMA doesn't merge with other VMAs.
-- 
2.42.0.655.g421f12c284-goog