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kcore: fix vread/vwrite to be aware of holes
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vread/vwrite access vmalloc area without checking there is a page or not.
In most case, this works well.

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.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Mike Smith <scgtrp@gmail.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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KAMEZAWA Hiroyuki authored and Linus Torvalds committed Sep 22, 2009
1 parent dd32c27 commit d0107eb
Showing 1 changed file with 176 additions and 23 deletions.
199 changes: 176 additions & 23 deletions mm/vmalloc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@
#include <linux/rcupdate.h>
#include <linux/pfn.h>
#include <linux/kmemleak.h>

#include <linux/highmem.h>
#include <asm/atomic.h>
#include <asm/uaccess.h>
#include <asm/tlbflush.h>
Expand Down Expand Up @@ -1643,18 +1643,128 @@ void *vmalloc_32_user(unsigned long size)
}
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 = 0;

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);
/*
* To do safe access to this _mapped_ area, we need
* lock. But adding lock here means that we need to add
* overhead of vmalloc()/vfree() calles for this _debug_
* interface, rarely used. Instead of that, we'll use
* kmap() and get small overhead in this access function.
*/
if (p) {
/*
* we can expect USER0 is not used (see vread/vwrite's
* function description)
*/
void *map = kmap_atomic(p, KM_USER0);
memcpy(buf, map + offset, length);
kunmap_atomic(map, KM_USER0);
} else
memset(buf, 0, length);

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 = 0;

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);
/*
* To do safe access to this _mapped_ area, we need
* lock. But adding lock here means that we need to add
* overhead of vmalloc()/vfree() calles for this _debug_
* interface, rarely used. Instead of that, we'll use
* kmap() and get small overhead in this access function.
*/
if (p) {
/*
* we can expect USER0 is not used (see vread/vwrite's
* function description)
*/
void *map = kmap_atomic(p, KM_USER0);
memcpy(map + offset, buf, length);
kunmap_atomic(map, KM_USER0);
}
addr += length;
buf += length;
copied += length;
count -= length;
}
return copied;
}

/**
* vread() - read vmalloc area 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 should be increased.
* (same number to @count). Returns 0 if [addr...addr+count) doesn't
* includes any intersect with alive vmalloc area.
*
* This function checks that addr is a valid vmalloc'ed area, and
* copy data from that area to a given buffer. If the 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.
*
* If [addr...addr+count) doesn't includes any intersects with alive
* vm_struct area, returns 0.
* @buf should be kernel's buffer. Because this function uses KM_USER0,
* the caller should guarantee KM_USER0 is not used.
*
* 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 */
if ((unsigned long) addr + count < count)
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;
Expand All @@ -1667,32 +1777,72 @@ long vread(char *buf, char *addr, unsigned long count)
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 a safe way.
* @buf: buffer for source data
* @addr: vm address.
* @count: number of bytes to be read.
*
* Returns # of bytes which addr and buf should be incresed.
* (same number to @count).
* If [addr...addr+count) doesn't includes any intersect with valid
* vmalloc area, returns 0.
*
* This function checks that addr is a valid vmalloc'ed area, and
* copy data from a buffer to the given addr. If specified range of
* [addr...addr+count) includes some valid address, data is copied from
* proper area of @buf. If there are memory holes, no copy to hole.
* IOREMAP area is treated as memory hole and no copy is done.
*
* If [addr...addr+count) doesn't includes any intersects with alive
* vm_struct area, returns 0.
* @buf should be kernel's buffer. Because this function uses KM_USER0,
* the caller should guarantee KM_USER0 is not used.
*
* 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.
*
* The caller should guarantee KM_USER1 is not used.
*/

long vwrite(char *buf, char *addr, unsigned long count)
{
struct vm_struct *tmp;
char *vaddr, *buf_start = buf;
unsigned long n;
char *vaddr;
unsigned long n, buflen;
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;
Expand All @@ -1704,18 +1854,21 @@ long vwrite(char *buf, char *addr, unsigned long count)
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;
}

/**
Expand Down

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