[PATCH 3/3] HWPOISON: prevent /dev/kmem users from accessing hwpoison pages

[Wu Fengguang]

When /dev/kmem read()/write() encounters hwpoison page, stop it
and return the amount of work done till now.

Vmalloc pages are not checked for now, to avoid conflicts with
ongoing vread/vwrite works.

CC: Greg KH <greg@xxxxxxxxx>
CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
CC: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
CC: Nick Piggin <npiggin@xxxxxxx>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 drivers/char/mem.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- linux-mm.orig/drivers/char/mem.c	2009-09-16 09:25:34.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-09-16 09:25:43.000000000 +0800
@@ -427,6 +427,9 @@ static ssize_t read_kmem(struct file *fi
 			 */
 			kbuf = xlate_dev_kmem_ptr((char *)p);
 
+			if (unlikely(virt_addr_valid(kbuf) &&
+				     PageHWPoison(virt_to_page(kbuf))))
+				return -EIO;
 			if (copy_to_user(buf, kbuf, sz))
 				return -EFAULT;
 			buf += sz;
@@ -472,6 +475,7 @@ do_write_kmem(unsigned long p, const cha
 {
 	ssize_t written, sz;
 	unsigned long copied;
+	int err = 0;
 
 	written = 0;
 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
@@ -498,13 +502,19 @@ do_write_kmem(unsigned long p, const cha
 		 */
 		ptr = xlate_dev_kmem_ptr((char *)p);
 
+		if (unlikely(virt_addr_valid(ptr) &&
+			     PageHWPoison(virt_to_page(ptr)))) {
+			err = -EIO;
+			break;
+		}
+
 		copied = copy_from_user(ptr, buf, sz);
 		if (copied) {
 			written += sz - copied;
-			if (written)
-				break;
-			return -EFAULT;
+			err = -EFAULT;
+			break;
 		}
+
 		buf += sz;
 		p += sz;
 		count -= sz;
@@ -512,7 +522,7 @@ do_write_kmem(unsigned long p, const cha
 	}
 
 	*ppos += written;
-	return written;
+	return written ? written : err;
 }
 
 

-- 

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