From: Dan Williams dan.j.williams@intel.com Subject: device-dax: implement ->split() to catch invalid munmap attempts

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@dwillia... 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 ---

drivers/dax/device.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff -puN drivers/dax/device.c~device-dax-implement-split-to-catch-invalid-munmap-attempts drivers/dax/device.c --- a/drivers/dax/device.c~device-dax-implement-split-to-catch-invalid-munmap-attempts +++ a/drivers/dax/device.c @@ -428,9 +428,21 @@ static int dev_dax_fault(struct vm_fault return dev_dax_huge_fault(vmf, PE_SIZE_PTE); }

+static int dev_dax_split(struct vm_area_struct *vma, unsigned long addr) +{ + struct file *filp = vma->vm_file; + struct dev_dax *dev_dax = filp->private_data; + struct dax_region *dax_region = dev_dax->region; + + if (!IS_ALIGNED(addr, dax_region->align)) + return -EINVAL; + return 0; +} + static const struct vm_operations_struct dax_vm_ops = { .fault = dev_dax_fault, .huge_fault = dev_dax_huge_fault, + .split = dev_dax_split, };

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