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Subject[PATCH 4.9 32/39] device-dax: implement ->split() to catch invalid munmap attempts
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@intel.com>

commit 9702cffdbf2129516db679e4467db81e1cd287da upstream.

Similar to how device-dax enforces that the 'address', 'offset', and
'len' parameters to mmap() be aligned to the device's fundamental
alignment, the same constraints apply to munmap(). Implement ->split()
to fail munmap calls that violate the alignment constraint.

Otherwise, we later fail VM_BUG_ON checks in the unmap_page_range() path
with crash signatures of the form:

vma ffff8800b60c8a88 start 00007f88c0000000 end 00007f88c0e00000
next (null) prev (null) mm ffff8800b61150c0
prot 8000000000000027 anon_vma (null) vm_ops ffffffffa0091240
pgoff 0 file ffff8800b638ef80 private_data (null)
flags: 0x380000fb(read|write|shared|mayread|maywrite|mayexec|mayshare|softdirty|mixedmap|hugepage)
------------[ cut here ]------------
kernel BUG at mm/huge_memory.c:2014!
[..]
RIP: 0010:__split_huge_pud+0x12a/0x180
[..]
Call Trace:
unmap_page_range+0x245/0xa40
? __vma_adjust+0x301/0x990
unmap_vmas+0x4c/0xa0
unmap_region+0xae/0x120
? __vma_rb_erase+0x11a/0x230
do_munmap+0x276/0x410
vm_munmap+0x6a/0xa0
SyS_munmap+0x1d/0x30

Link: http://lkml.kernel.org/r/151130418681.4029.7118245855057952010.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/dax/dax.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -453,9 +453,21 @@ static int dax_dev_pmd_fault(struct vm_a
return rc;
}

+static int dax_dev_split(struct vm_area_struct *vma, unsigned long addr)
+{
+ struct file *filp = vma->vm_file;
+ struct dax_dev *dax_dev = filp->private_data;
+ struct dax_region *dax_region = dax_dev->region;
+
+ if (!IS_ALIGNED(addr, dax_region->align))
+ return -EINVAL;
+ return 0;
+}
+
static const struct vm_operations_struct dax_dev_vm_ops = {
.fault = dax_dev_fault,
.pmd_fault = dax_dev_pmd_fault,
+ .split = dax_dev_split,
};

static int dax_mmap(struct file *filp, struct vm_area_struct *vma)

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