[PATCH] hugetlb: prepare_hugepage_range check offset too

(David:)

If hugetlbfs_file_mmap() returns a failure to do_mmap_pgoff() - for example,
because the given file offset is not hugepage aligned - then do_mmap_pgoff
will go to the unmap_and_free_vma backout path.

But at this stage the vma hasn't been marked as hugepage, and the backout path
will call unmap_region() on it.  That will eventually call down to the
non-hugepage version of unmap_page_range().  On ppc64, at least, that will
cause serious problems if there are any existing hugepage pagetable entries in
the vicinity - for example if there are any other hugepage mappings under the
same PUD.  unmap_page_range() will trigger a bad_pud() on the hugepage pud
entries.  I suspect this will also cause bad problems on ia64, though I don't
have a machine to test it on.

(Hugh:)

prepare_hugepage_range() should check file offset alignment when it checks
virtual address and length, to stop MAP_FIXED with a bad huge offset from
unmapping before it fails further down.  PowerPC should apply the same
prepare_hugepage_range alignment checks as ia64 and all the others do.

Then none of the alignment checks in hugetlbfs_file_mmap are required (nor
is the check for too small a mapping); but even so, move up setting of
VM_HUGETLB and add a comment to warn of what David Gibson discovered - if
hugetlbfs_file_mmap fails before setting it, do_mmap_pgoff's unmap_region
when unwinding from error will go the non-huge way, which may cause bad
behaviour on architectures (powerpc and ia64) which segregate their huge
mappings into a separate region of the address space.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: Adam Litke <agl@us.ibm.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 13 deletions

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 0bea6a619e10..7f4756963d05 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -62,24 +62,19 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
         loff_t len, vma_len;
         int ret;
 
-        if (vma->vm_pgoff & (HPAGE_SIZE / PAGE_SIZE - 1))
-                return -EINVAL;
-
-        if (vma->vm_start & ~HPAGE_MASK)
-                return -EINVAL;
-
-        if (vma->vm_end & ~HPAGE_MASK)
-                return -EINVAL;
-
-        if (vma->vm_end - vma->vm_start < HPAGE_SIZE)
-                return -EINVAL;
+        /*
+         * vma alignment has already been checked by prepare_hugepage_range.
+         * If you add any error returns here, do so after setting VM_HUGETLB,
+         * so is_vm_hugetlb_page tests below unmap_region go the right way
+         * when do_mmap_pgoff unwinds (may be important on powerpc and ia64).
+         */
+        vma->vm_flags |= VM_HUGETLB | VM_RESERVED;
+        vma->vm_ops = &hugetlb_vm_ops;
 
         vma_len = (loff_t)(vma->vm_end - vma->vm_start);
 
         mutex_lock(&inode->i_mutex);
         file_accessed(file);
-        vma->vm_flags |= VM_HUGETLB | VM_RESERVED;
-        vma->vm_ops = &hugetlb_vm_ops;
 
         ret = -ENOMEM;
         len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);