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Revert "mm: introduce VM_POPULATE flag to better deal with racy userspace programs"

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This reverts commit 1869305009 ("mm: introduce VM_POPULATE flag to
better deal with racy userspace programs").

VM_POPULATE only has any effect when userspace plays racy games with
vmas by trying to unmap and remap memory regions that mmap or mlock are
operating on.

Also, the only effect of VM_POPULATE when userspace plays such games is
that it avoids populating new memory regions that get remapped into the
address range that was being operated on by the original mmap or mlock
calls.

Let's remove VM_POPULATE as there isn't any strong argument to mandate a
new vm_flag.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2013-03-28 16:26:23 -07:00 committed by Linus Torvalds
parent 0776ce03b1
commit 09a9f1d278
5 changed files with 11 additions and 21 deletions
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1
include/linux/mm.h
View File

@ -87,7 +87,6 @@ extern unsigned int kobjsize(const void *objp);
#define VM_PFNMAP 0x00000400 /* Page-ranges managed without "struct page", just pure PFN */
#define VM_DENYWRITE 0x00000800 /* ETXTBSY on write attempts.. */
#define VM_POPULATE 0x00001000
#define VM_LOCKED 0x00002000
#define VM_IO 0x00004000 /* Memory mapped I/O or similar */

4
include/linux/mman.h
View File

@ -79,8 +79,6 @@ calc_vm_flag_bits(unsigned long flags)
{
return _calc_vm_trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN ) |
_calc_vm_trans(flags, MAP_DENYWRITE, VM_DENYWRITE ) |
((flags & MAP_LOCKED) ? (VM_LOCKED | VM_POPULATE) : 0) |
(((flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE) ?
VM_POPULATE : 0);
_calc_vm_trans(flags, MAP_LOCKED, VM_LOCKED );
}
#endif /* _LINUX_MMAN_H */

12
mm/fremap.c
View File

@ -204,10 +204,8 @@ get_write_lock:
unsigned long addr;
struct file *file = get_file(vma->vm_file);
vm_flags = vma->vm_flags;
if (!(flags & MAP_NONBLOCK))
vm_flags |= VM_POPULATE;
addr = mmap_region(file, start, size, vm_flags, pgoff);
addr = mmap_region(file, start, size,
vma->vm_flags, pgoff);
fput(file);
if (IS_ERR_VALUE(addr)) {
err = addr;
@ -226,12 +224,6 @@ get_write_lock:
mutex_unlock(&mapping->i_mmap_mutex);
}
if (!(flags & MAP_NONBLOCK) && !(vma->vm_flags & VM_POPULATE)) {
if (!has_write_lock)
goto get_write_lock;
vma->vm_flags |= VM_POPULATE;
}
if (vma->vm_flags & VM_LOCKED) {
/*
* drop PG_Mlocked flag for over-mapped range

11
mm/mlock.c
View File

@ -358,7 +358,7 @@ static int do_mlock(unsigned long start, size_t len, int on)
newflags = vma->vm_flags & ~VM_LOCKED;
if (on)
newflags |= VM_LOCKED | VM_POPULATE;
newflags |= VM_LOCKED;
tmp = vma->vm_end;
if (tmp > end)
@ -418,8 +418,7 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
* range with the first VMA. Also, skip undesirable VMA types.
*/
nend = min(end, vma->vm_end);
if ((vma->vm_flags & (VM_IO | VM_PFNMAP | VM_POPULATE)) !=
VM_POPULATE)
if (vma->vm_flags & (VM_IO | VM_PFNMAP))
continue;
if (nstart < vma->vm_start)
nstart = vma->vm_start;
@ -492,9 +491,9 @@ static int do_mlockall(int flags)
struct vm_area_struct * vma, * prev = NULL;
if (flags & MCL_FUTURE)
current->mm->def_flags |= VM_LOCKED | VM_POPULATE;
current->mm->def_flags |= VM_LOCKED;
else
current->mm->def_flags &= ~(VM_LOCKED | VM_POPULATE);
current->mm->def_flags &= ~VM_LOCKED;
if (flags == MCL_FUTURE)
goto out;
@ -503,7 +502,7 @@ static int do_mlockall(int flags)
newflags = vma->vm_flags & ~VM_LOCKED;
if (flags & MCL_CURRENT)
newflags |= VM_LOCKED | VM_POPULATE;
newflags |= VM_LOCKED;
/* Ignore errors */
mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);

4
mm/mmap.c
View File

@ -1306,7 +1306,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
}
addr = mmap_region(file, addr, len, vm_flags, pgoff);
if (!IS_ERR_VALUE(addr) && (vm_flags & VM_POPULATE))
if (!IS_ERR_VALUE(addr) &&
((vm_flags & VM_LOCKED) ||
(flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
*populate = len;
return addr;
}