Re: [BUGFIX][PATCH 1/3] fix vread/vwrite to be aware of memory hole

[Amerigo Wang <xiyou.wangcong@gmail.com>]

On Fri, Jul 31, 2009 at 04:11:28PM +0900, KAMEZAWA Hiroyuki wrote:
>From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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;
> }
> 
> /**
>