[RFC][PATCH 2/2] vmalloc: vread vwrite avoid memory hole.
From: KAMEZAWA Hiroyuki
Date: Wed Jul 29 2009 - 04:50:15 EST
Considering recent changes, I think this an answer to this bug.
All get_vm_area() calls specified VM_IOREMAP before 2.6.30.
Now, percpu calls get_vm_area() without IOREMAP (it means kcore doesn't skip this)
And it seems pcpu does delayed map to pre-allocated vmalloc-area.
Then, now, vmalloc() area has memory holes. (I'm sorry if I misunderstand.)
Then, vread()/vwrite() should be aware of memory holes in vmalloc.
And yes, /proc/kcore should be.
plz review.
==
vread/vwrite access vmalloc area without checking there is a page or not.
In most case, this works well.
After per-cpu-alloc patch, There tend to be a hole in valid vmalloc area.
Then, skip the hole (not mapped page) is necessary.
/proc/kcore has the same problem, now, it uses its own code but
it's better to use vread().
Question: vread() should skip IOREMAP area always ?
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
drivers/char/mem.c | 3 +
fs/proc/kcore.c | 32 +----------------
include/linux/vmalloc.h | 3 +
mm/vmalloc.c | 90 +++++++++++++++++++++++++++++++++++++-----------
4 files changed, 77 insertions(+), 51 deletions(-)
Index: linux-2.6.31-rc4/mm/vmalloc.c
===================================================================
--- linux-2.6.31-rc4.orig/mm/vmalloc.c
+++ linux-2.6.31-rc4/mm/vmalloc.c
@@ -1629,7 +1629,61 @@ void *vmalloc_32_user(unsigned long size
}
EXPORT_SYMBOL(vmalloc_32_user);
-long vread(char *buf, char *addr, unsigned long count)
+/*
+ * 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 = (unsinged 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);
+ addr += length;
+ buf += length;
+ copiled += 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 = (unsinged 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);
+ addr += length;
+ buf += length;
+ copiled += length;
+ count -= length;
+ }
+ return copied;
+}
+
+long vread(char *buf, char *addr, unsigned long count, bool skip_ioremap)
{
struct vm_struct *tmp;
char *vaddr, *buf_start = buf;
@@ -1640,10 +1694,11 @@ long vread(char *buf, char *addr, unsign
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;
+
while (addr < vaddr) {
if (count == 0)
goto finished;
@@ -1653,14 +1708,15 @@ long vread(char *buf, char *addr, unsign
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) || !skip_ioremap)
+ aligned_vread(buf, addr, n);
+ else
+ memset(buf, 0, n);
+ buf += n;
+ addr += n;
+ count -= n;
}
finished:
read_unlock(&vmlist_lock);
@@ -1678,7 +1734,7 @@ long vwrite(char *buf, char *addr, unsig
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;
@@ -1690,14 +1746,10 @@ long vwrite(char *buf, char *addr, unsig
count--;
}
n = vaddr + tmp->size - PAGE_SIZE - addr;
- do {
- if (count == 0)
- goto finished;
- *addr = *buf;
- buf++;
- addr++;
- count--;
- } while (--n > 0);
+ copied = aligned_vwrite(buf, addr, n);
+ buf += n;
+ addr += n;
+ count -= n;
}
finished:
read_unlock(&vmlist_lock);
Index: linux-2.6.31-rc4/drivers/char/mem.c
===================================================================
--- linux-2.6.31-rc4.orig/drivers/char/mem.c
+++ linux-2.6.31-rc4/drivers/char/mem.c
@@ -466,7 +466,8 @@ static ssize_t read_kmem(struct file *fi
if (len > PAGE_SIZE)
len = PAGE_SIZE;
- len = vread(kbuf, (char *)p, len);
+ /* we read memory even if ioremap...*/
+ len = vread(kbuf, (char *)p, len, false);
if (!len)
break;
if (copy_to_user(buf, kbuf, len)) {
Index: linux-2.6.31-rc4/fs/proc/kcore.c
===================================================================
--- linux-2.6.31-rc4.orig/fs/proc/kcore.c
+++ linux-2.6.31-rc4/fs/proc/kcore.c
@@ -331,40 +331,12 @@ read_kcore(struct file *file, char __use
struct vm_struct *m;
unsigned long curstart = start;
unsigned long cursize = tsz;
-
+
elf_buf = kzalloc(tsz, GFP_KERNEL);
if (!elf_buf)
return -ENOMEM;
- read_lock(&vmlist_lock);
- for (m=vmlist; m && cursize; m=m->next) {
- unsigned long vmstart;
- unsigned long vmsize;
- unsigned long msize = m->size - PAGE_SIZE;
-
- if (((unsigned long)m->addr + msize) <
- curstart)
- continue;
- if ((unsigned long)m->addr > (curstart +
- cursize))
- break;
- vmstart = (curstart < (unsigned long)m->addr ?
- (unsigned long)m->addr : curstart);
- if (((unsigned long)m->addr + msize) >
- (curstart + cursize))
- vmsize = curstart + cursize - vmstart;
- else
- vmsize = (unsigned long)m->addr +
- msize - vmstart;
- curstart = vmstart + vmsize;
- cursize -= vmsize;
- /* don't dump ioremap'd stuff! (TA) */
- if (m->flags & VM_IOREMAP)
- continue;
- memcpy(elf_buf + (vmstart - start),
- (char *)vmstart, vmsize);
- }
- read_unlock(&vmlist_lock);
+ vread(elf_buf, start, tsz, true);
if (copy_to_user(buffer, elf_buf, tsz)) {
kfree(elf_buf);
return -EFAULT;
Index: linux-2.6.31-rc4/include/linux/vmalloc.h
===================================================================
--- linux-2.6.31-rc4.orig/include/linux/vmalloc.h
+++ linux-2.6.31-rc4/include/linux/vmalloc.h
@@ -105,7 +105,8 @@ extern struct vm_struct *alloc_vm_area(s
extern void free_vm_area(struct vm_struct *area);
/* for /dev/kmem */
-extern long vread(char *buf, char *addr, unsigned long count);
+extern long vread(char *buf, char *addr, unsigned long count,
+ bool skip_ioremap);
extern long vwrite(char *buf, char *addr, unsigned long count);
/*
--
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