Hello,
On 2013-10-17 23:23, Jan Kara wrote:
I'm auditing get_user_pages() users and when looking into
vb2_dc_get_userptr() I was wondering about the following: The address this
function works with is an arbitrary user-provided address. However the
function vb2_dc_get_user_pages() uses pfn_to_page() on the pfn obtained
from VM_IO | VM_PFNMAP vma. That isn't really safe for arbitrary vma of
this type (such vmas don't have to have struct page associated at all). I
expect this works because userspace always passes a pointer to either a
regular vma or VM_FIXMAP vma where struct page is associated with pfn. Am
I right? Or for on which vmas this code is supposed to work? Thanks in
advance for clarification.
This is known issue. It has been at least partially addresses by the
following patch:
https://patchwork.linuxtv.org/patch/18978/
I hope that one day it can be addressed fully by changing the
dma-mapping API in a way it will let drivers to map particular pfn into
dma address space.
Best regards
--
Marek Szyprowski
Samsung R&D Institute Poland
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