[PATCH 2/4] hwpoison: prevent /dev/mem from accessing hwpoison pages

[Wu Fengguang]

Return EIO when user space tries to read/write/mmap hwpoison pages
via the /dev/mem interface.

The approach: rename range_is_allowed() to devmem_check_pfn_range(), and
add PageHWPoison() test in it. This function will be called for the whole
mmap() range, or page by page for read()/write(). So it would fail the
mmap() request as a whole, and return partial results for read()/write().

CC: Greg KH <greg@xxxxxxxxx>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 drivers/char/mem.c |   39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

--- linux-mm.orig/drivers/char/mem.c	2009-12-29 10:47:00.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-12-29 10:54:07.000000000 +0800
@@ -89,31 +89,28 @@ static inline int valid_mmap_phys_addr_r
 }
 #endif
 
-#ifdef CONFIG_STRICT_DEVMEM
-static inline int range_is_allowed(unsigned long pfn, unsigned long size)
+static int devmem_check_pfn_range(unsigned long pfn, unsigned long bytes)
 {
 	u64 from = ((u64)pfn) << PAGE_SHIFT;
-	u64 to = from + size;
+	u64 to = from + bytes;
 	u64 cursor = from;
 
 	while (cursor < to) {
+#ifdef CONFIG_STRICT_DEVMEM
 		if (!devmem_is_allowed(pfn)) {
 			printk(KERN_INFO
 		"Program %s tried to access /dev/mem between %Lx->%Lx.\n",
 				current->comm, from, to);
-			return 0;
+			return -EPERM;
 		}
+#endif
+		if (pfn_valid(pfn) && PageHWPoison(pfn_to_page(pfn)))
+			return -EIO;
 		cursor += PAGE_SIZE;
 		pfn++;
 	}
-	return 1;
-}
-#else
-static inline int range_is_allowed(unsigned long pfn, unsigned long size)
-{
-	return 1;
+	return 0;
 }
-#endif
 
 void __attribute__((weak)) unxlate_dev_mem_ptr(unsigned long phys, void *addr)
 {
@@ -150,11 +147,13 @@ static ssize_t read_mem(struct file * fi
 
 	while (count > 0) {
 		unsigned long remaining;
+		int err;
 
 		sz = size_inside_page(p, count);
 
-		if (!range_is_allowed(p >> PAGE_SHIFT, count))
-			return -EPERM;
+		err = devmem_check_pfn_range(p >> PAGE_SHIFT, count);
+		if (err)
+			return err;
 
 		/*
 		 * On ia64 if a page has been mapped somewhere as
@@ -184,9 +183,10 @@ static ssize_t write_mem(struct file * f
 			 size_t count, loff_t *ppos)
 {
 	unsigned long p = *ppos;
-	ssize_t written, sz;
 	unsigned long copied;
+	ssize_t written, sz;
 	void *ptr;
+	int err;
 
 	if (!valid_phys_addr_range(p, count))
 		return -EFAULT;
@@ -208,8 +208,9 @@ static ssize_t write_mem(struct file * f
 	while (count > 0) {
 		sz = size_inside_page(p, count);
 
-		if (!range_is_allowed(p >> PAGE_SHIFT, sz))
-			return -EPERM;
+		err = devmem_check_pfn_range(p >> PAGE_SHIFT, sz);
+		if (err)
+			return err;
 
 		/*
 		 * On ia64 if a page has been mapped somewhere as
@@ -297,6 +298,7 @@ static const struct vm_operations_struct
 static int mmap_mem(struct file * file, struct vm_area_struct * vma)
 {
 	size_t size = vma->vm_end - vma->vm_start;
+	int err;
 
 	if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
 		return -EINVAL;
@@ -304,8 +306,9 @@ static int mmap_mem(struct file * file, 
 	if (!private_mapping_ok(vma))
 		return -ENOSYS;
 
-	if (!range_is_allowed(vma->vm_pgoff, size))
-		return -EPERM;
+	err = devmem_check_pfn_range(vma->vm_pgoff, size);
+	if (err)
+		return err;
 
 	if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
 						&vma->vm_page_prot))


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