[BUGFIX][PATCH 1/3] fix vread/vwrite to be aware of memory hole
From: KAMEZAWA Hiroyuki
Date: Fri Jul 31 2009 - 03:13:22 EST
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
vread/vwrite access vmalloc area without checking there is a page or not.
In old ages, the caller of get_vm_ara() is only IOREMAP and there is no
memory hole within vm_struct's [addr...addr + size - PAGE_SIZE]
( -PAGE_SIZE is for a guard page.)
After per-cpu-alloc patch, it uses get_vm_area() for reserve continuous
virtual address but remap _later_. There tend to be a hole in valid vmalloc
area in vm_struct lists.
Then, skip the hole (not mapped page) is necessary.
This patch updates vread/vwrite() for avoiding memory hole.
Routines which access vmalloc area without knowing for which addr is used
are
- /proc/kcore
- /dev/kmem
kcore checks IOREMAP, /dev/kmem doesn't. After this patch, IOREMAP is
checked and /dev/kmem will avoid to read/write it.
Fixes to /proc/kcore will be in the next patch in series.
And, this itself fixes the bug as
# dd if=/dev/kmem of=/dev/null bs=1024 count=1048576 skip=3145728
can cause panic.
Changelog v1->v2:
- enhanced comments.
- treat IOREMAP as hole always.
- zero-fill memory hole if [addr...addr+size] includes valid pages.
- returns 0 if [addr...addr+size) includes no valid pages.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/vmalloc.c | 157 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 136 insertions(+), 21 deletions(-)
Index: linux-2.6.31-rc4/mm/vmalloc.c
===================================================================
--- linux-2.6.31-rc4.orig/mm/vmalloc.c 2009-07-31 14:06:41.000000000 +0900
+++ linux-2.6.31-rc4/mm/vmalloc.c 2009-07-31 15:51:56.000000000 +0900
@@ -1625,10 +1625,89 @@
}
EXPORT_SYMBOL(vmalloc_32_user);
+/*
+ * small helper routine , copy contents to buf from addr.
+ * If the page is not present, fill zero.
+ */
+
+static int aligned_vread(char *buf, char *addr, unsigned long count)
+{
+ struct page *p;
+ int copied;
+
+ while (count) {
+ unsigned long offset, length;
+
+ offset = (unsigned long)addr & PAGE_MASK;
+ length = PAGE_SIZE - offset;
+ if (length > count)
+ length = count;
+ p = vmalloc_to_page(addr);
+ if (p)
+ memcpy(buf, addr, length);
+ else
+ memset(buf, 0, length);
+ /* If no page, we fill 0 this area and incremetns buffer addr */
+ addr += length;
+ buf += length;
+ copied += length;
+ count -= length;
+ }
+ return copied;
+}
+
+static int aligned_vwrite(char *buf, char *addr, unsigned long count)
+{
+ struct page *p;
+ int copied;
+
+ while (count) {
+ unsigned long offset, length;
+
+ offset = (unsigned long)addr & PAGE_MASK;
+ length = PAGE_SIZE - offset;
+ if (length > count)
+ length = count;
+ /* confirm the page is present */
+ p = vmalloc_to_page(addr);
+ if (p)
+ memcpy(addr, buf, length);
+ /* If no page, we skip this area but incremetns buffer addr */
+ addr += length;
+ buf += length;
+ copied += length;
+ count -= length;
+ }
+ return copied;
+}
+
+/**
+ * vread() - read vmalloc area in safe way.
+ * @buf: buffer for reading data
+ * @addr: vm address.
+ * @count: number of bytes to be read.
+ *
+ * Returns # of bytes which addr and buf shuld be incremented
+ * (same to count).
+ * If [addr...addr+count) doesn't includes any valid area, returns 0.
+ *
+ * This function checks that addr is a valid vmalloc'ed area, and
+ * copy data from that area to given buffer. If given memory range of
+ * [addr...addr+count) includes some valid address, data is copied to
+ * proper area of @buf. If there are memory holes, they'll be zero-filled.
+ * IOREMAP area is treated as memory hole and no copy is done.
+ *
+ * Note: In usual ops, vread() is never necessary because the caller should
+ * know vmalloc() area is valid and can use memcpy(). This is for routines
+ * which have to access vmalloc area without any informaion, as /dev/kmem.
+ *
+ */
+
long vread(char *buf, char *addr, unsigned long count)
{
struct vm_struct *tmp;
char *vaddr, *buf_start = buf;
+ unsigned long buflen = count;
unsigned long n;
/* Don't allow overflow */
@@ -1636,7 +1715,7 @@
count = -(unsigned long) addr;
read_lock(&vmlist_lock);
- for (tmp = vmlist; tmp; tmp = tmp->next) {
+ for (tmp = vmlist; count && tmp; tmp = tmp->next) {
vaddr = (char *) tmp->addr;
if (addr >= vaddr + tmp->size - PAGE_SIZE)
continue;
@@ -1649,32 +1728,65 @@
count--;
}
n = vaddr + tmp->size - PAGE_SIZE - addr;
- do {
- if (count == 0)
- goto finished;
- *buf = *addr;
- buf++;
- addr++;
- count--;
- } while (--n > 0);
+ if (n > count)
+ n = count;
+ if (!(tmp->flags & VM_IOREMAP))
+ aligned_vread(buf, addr, n);
+ else /* IOREMAP area is treated as memory hole */
+ memset(buf, 0, n);
+ buf += n;
+ addr += n;
+ count -= n;
}
finished:
read_unlock(&vmlist_lock);
- return buf - buf_start;
+
+ if (buf == buf_start)
+ return 0;
+ /* zero-fill memory holes */
+ if (buf != buf_start + buflen)
+ memset(buf, 0, buflen - (buf - buf_start));
+
+ return buflen;
}
+/**
+ * vwrite() - write vmalloc area in safe way.
+ * @buf: buffer for source data
+ * @addr: vm address.
+ * @count: number of bytes to be read.
+ *
+ * Returns # of bytes which addr and buf shuld be incremented
+ * (same to count).
+ * If [addr...addr+count) doesn't includes any valid area, returns 0.
+ *
+ * This function checks that addr is a valid vmalloc'ed area, and
+ * copy data from that buffer to there. If given memory range of
+ * [addr...addr+count) includes some valid address, data is copied from
+ * proper area of @buf. If there are memory holes, no copy. just skip.
+ * IOREMAP area is treated as memory hole and no copy is done.
+ *
+ * Note: In usual ops, vwrite() is never necessary because the caller
+ * should know vmalloc() area is valid and can use memcpy().
+ * This is for routines which have to access vmalloc area without
+ * any informaion, as /dev/kmem.
+ */
+
long vwrite(char *buf, char *addr, unsigned long count)
{
struct vm_struct *tmp;
- char *vaddr, *buf_start = buf;
+ char *vaddr;
+ unsigned long buflen;
unsigned long n;
+ int copied = 0;
/* Don't allow overflow */
if ((unsigned long) addr + count < count)
count = -(unsigned long) addr;
+ buflen = count;
read_lock(&vmlist_lock);
- for (tmp = vmlist; tmp; tmp = tmp->next) {
+ for (tmp = vmlist; count && tmp; tmp = tmp->next) {
vaddr = (char *) tmp->addr;
if (addr >= vaddr + tmp->size - PAGE_SIZE)
continue;
@@ -1686,18 +1798,21 @@
count--;
}
n = vaddr + tmp->size - PAGE_SIZE - addr;
- do {
- if (count == 0)
- goto finished;
- *addr = *buf;
- buf++;
- addr++;
- count--;
- } while (--n > 0);
+ if (n > count)
+ n = count;
+ if (!(tmp->flags & VM_IOREMAP)) {
+ aligned_vwrite(buf, addr, n);
+ copied++;
+ }
+ buf += n;
+ addr += n;
+ count -= n;
}
finished:
read_unlock(&vmlist_lock);
- return buf - buf_start;
+ if (!copied)
+ return 0;
+ return buflen;
}
/**
--
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