Re: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem)

[Linus Torvalds <torvalds@osdl.org>]

On Sat, 13 Aug 2005, Arjan van de Ven wrote:
> 
> attached is the same patch but now with Steven's change made as well

Actually, the more I looked at that mmap_kmem() function, the less I liked 
it.  Let's get that sucker fixed better first. It's still not wonderful, 
but at least now it tries to verify the whole _range_ of the mapping.

Steven, does this "alternate mmap_kmem fix" patch work for you?

		Linus
----
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -261,7 +261,11 @@ static int mmap_mem(struct file * file, 
 
 static int mmap_kmem(struct file * file, struct vm_area_struct * vma)
 {
-        unsigned long long val;
+	unsigned long pfn, size;
+
+	/* Turn a kernel-virtual address into a physical page frame */
+	pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT;
+
 	/*
 	 * RED-PEN: on some architectures there is more mapped memory
 	 * than available in mem_map which pfn_valid checks
@@ -269,10 +273,14 @@ static int mmap_kmem(struct file * file,
 	 *
 	 * RED-PEN: vmalloc is not supported right now.
 	 */
-	if (!pfn_valid(vma->vm_pgoff))
+	if (!pfn_valid(pfn))
 		return -EIO;
-	val = (u64)vma->vm_pgoff << PAGE_SHIFT;
-	vma->vm_pgoff = __pa(val) >> PAGE_SHIFT;
+
+	size = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	if (!pfn_valid(pfn + size - 1))
+		return -EIO;
+
+	vma->vm_pgoff = pfn;
 	return mmap_mem(file, vma);
 }
 
-
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