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Date: Fri, 31 Jul 2009 19:32:15 +0900 (JST)
From: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To: "Amerigo Wang" <xiyou.wangcong@...il.com>
Cc: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
"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
Amerigo Wang さんは書きました：
> 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?
>
It directly reboot ;( and no log.
plz try.
>
>>
>>
>>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.
>
Ouch, thanks.
>
>>---
>> 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??
>
Ah, yes. should be fixed.
>>+
>>+ 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/
>
ok.
>
>>+ 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
>
Hmm..I though I removed all warnings..but it was an illusion..
ok, will fix.
>>+
>>+ 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
>
ok
>
>>+ addr += length;
>>+ buf += length;
>>+ copied += length;
>>+ count -= length;
>>+ }
>>+ return copied;
>>+}
>>+
>>+/**
>>+ * vread() - read vmalloc area in safe way.
>
> in _a_ safe way...
>
ok.
>
>>+ * @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/
>
ok.
>
>>+ * (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...
>
ok.
>
>>+ * [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?
>
I wrote "filled by zero" and thinks it's sane, then does this.
Now, /proc/kcore allocates memory by kzalloc(), this is redundant.
/dev/kmem doesn't do that.
>>+
>>+ 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
>
ouch..
Thank you for review.
I'm sorry that new version will not appear until next week.
I can't access x86-32 in the weekend.
Regards,
-Kame
>>+
>> 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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