kcore: fix vread/vwrite to be aware of holes

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>

1 files changed, 176 insertions, 23 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c4071fa8e12a..9216b2555d07 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -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>
@@ -1643,10 +1643,120 @@ 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 */
@@ -1654,7 +1764,7 @@ long vread(char *buf, char *addr, unsigned long 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;
@@ -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;
@@ -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;
 }
 
 /**