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Date: Fri, 31 Jul 2009 17:57:05 +0800
From: Amerigo Wang <xiyou.wangcong@...il.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Mike Smith <scgtrp@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
bugzilla-daemon@...zilla.kernel.org,
bugme-daemon@...zilla.kernel.org,
Amerigo Wang <xiyou.wangcong@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX][PATCH 1/3] fix vread/vwrite to be aware of memory hole
On Fri, Jul 31, 2009 at 04:11:28PM +0900, KAMEZAWA Hiroyuki wrote:
>From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
>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.
What panic? :-) Would you mind to put it here?
>
>
>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@...fujitsu.com>
I am sorry that there are still some typos below.
>---
> 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;
Forgot to initialize it??
>+
>+ 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 */
s/incremetns/increments/
>+ 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;
ditto
>+
>+ 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 */
ditto
>+ addr += length;
>+ buf += length;
>+ copied += length;
>+ count -= length;
>+ }
>+ return copied;
>+}
>+
>+/**
>+ * vread() - read vmalloc area in safe way.
in _a_ 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
s/shuld/should/
s/incremented/increased/
>+ * (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
to _a_ given buffer. If _the_ given memory...
>+ * [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));
Is this necessary?
>+
>+ 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.
>+ */
ditto
>+
> 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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