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From:   Yu-cheng Yu <yu-cheng.yu@intel.com>
To:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs
Date:   Fri, 21 Sep 2018 08:03:48 -0700
Message-Id: <20180921150351.20898-25-yu-cheng.yu@intel.com>
In-Reply-To: <20180921150351.20898-1-yu-cheng.yu@intel.com>
References: <20180921150351.20898-1-yu-cheng.yu@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Create a guard area between VMAs, to detect memory corruption.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 include/linux/mm.h | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c4cc07baccda..3a823bdae09d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2443,24 +2443,34 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m
 static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_start = vma->vm_start;
+	unsigned long gap;
+
+	if (vma->vm_flags & VM_GROWSDOWN)
+		gap = stack_guard_gap;
+	else
+		gap = PAGE_SIZE;
+
+	vm_start -= gap;
+	if (vm_start > vma->vm_start)
+		vm_start = 0;
 
-	if (vma->vm_flags & VM_GROWSDOWN) {
-		vm_start -= stack_guard_gap;
-		if (vm_start > vma->vm_start)
-			vm_start = 0;
-	}
 	return vm_start;
 }
 
 static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_end = vma->vm_end;
+	unsigned long gap;
+
+	if (vma->vm_flags & VM_GROWSUP)
+		gap = stack_guard_gap;
+	else
+		gap = PAGE_SIZE;
+
+	vm_end += gap;
+	if (vm_end < vma->vm_end)
+		vm_end = -PAGE_SIZE;
 
-	if (vma->vm_flags & VM_GROWSUP) {
-		vm_end += stack_guard_gap;
-		if (vm_end < vma->vm_end)
-			vm_end = -PAGE_SIZE;
-	}
 	return vm_end;
 }
 
-- 
2.17.1