From: Peter Xu <[email protected]>
Alex reported invalid page pointer returned with pin_user_pages_remote() from
vfio after upstream commit 4b6c33b32296 ("vfio/type1: Prepare for batched
pinning with struct vfio_batch").
It turns out that it's not the fault of the vfio commit; however after vfio
switches to a full page buffer to store the page pointers it starts to expose
the problem easier.
The problem is for VM_PFNMAP vmas we should normally fail with an -EFAULT then
vfio will carry on to handle the MMIO regions. However when the bug triggered,
follow_page_mask() returned -EEXIST for such a page, which will jump over the
current page, leaving that entry in **pages untouched. However the caller is
not aware of it, hence the caller will reference the page as usual even if the
pointer data can be anything.
We had that -EEXIST logic since commit 1027e4436b6a ("mm: make GUP handle pfn
mapping unless FOLL_GET is requested") which seems very reasonable. It could
be that when we reworked GUP with FOLL_PIN we could have overlooked that
special path in commit 3faa52c03f44 ("mm/gup: track FOLL_PIN pages"), even if
that commit rightfully touched up follow_devmap_pud() on checking FOLL_PIN when
it needs to return an -EEXIST.
Attaching the Fixes to the FOLL_PIN rework commit, as it happened later than
1027e4436b6a.
Cc: Andrea Arcangeli <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
Reviewed-by: Claudio Imbrenda <[email protected]>
Reported-by: Alex Williamson <[email protected]>
Debugged-by: Alex Williamson <[email protected]>
Tested-by: Alex Williamson <[email protected]>
Signed-off-by: Peter Xu <[email protected]>
[jhubbard: added some tags, removed a reference to an out of tree module.]
Signed-off-by: John Hubbard <[email protected]>
---
mm/gup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/gup.c b/mm/gup.c
index a9d4d724aef7..80229ecf0114 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -465,7 +465,7 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, unsigned int flags)
{
/* No page to get reference */
- if (flags & FOLL_GET)
+ if (flags & (FOLL_GET | FOLL_PIN))
return -EFAULT;
if (flags & FOLL_TOUCH) {
--
2.35.1
On Thu 03-02-22 18:00:06, John Hubbard wrote:
> From: Peter Xu <[email protected]>
>
> Alex reported invalid page pointer returned with pin_user_pages_remote() from
> vfio after upstream commit 4b6c33b32296 ("vfio/type1: Prepare for batched
> pinning with struct vfio_batch").
>
> It turns out that it's not the fault of the vfio commit; however after vfio
> switches to a full page buffer to store the page pointers it starts to expose
> the problem easier.
>
> The problem is for VM_PFNMAP vmas we should normally fail with an -EFAULT then
> vfio will carry on to handle the MMIO regions. However when the bug triggered,
> follow_page_mask() returned -EEXIST for such a page, which will jump over the
> current page, leaving that entry in **pages untouched. However the caller is
> not aware of it, hence the caller will reference the page as usual even if the
> pointer data can be anything.
>
> We had that -EEXIST logic since commit 1027e4436b6a ("mm: make GUP handle pfn
> mapping unless FOLL_GET is requested") which seems very reasonable. It could
> be that when we reworked GUP with FOLL_PIN we could have overlooked that
> special path in commit 3faa52c03f44 ("mm/gup: track FOLL_PIN pages"), even if
> that commit rightfully touched up follow_devmap_pud() on checking FOLL_PIN when
> it needs to return an -EEXIST.
>
> Attaching the Fixes to the FOLL_PIN rework commit, as it happened later than
> 1027e4436b6a.
>
> Cc: Andrea Arcangeli <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Jan Kara <[email protected]>
> Cc: Kirill A. Shutemov <[email protected]>
> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
> Reviewed-by: Claudio Imbrenda <[email protected]>
> Reported-by: Alex Williamson <[email protected]>
> Debugged-by: Alex Williamson <[email protected]>
> Tested-by: Alex Williamson <[email protected]>
> Signed-off-by: Peter Xu <[email protected]>
> [jhubbard: added some tags, removed a reference to an out of tree module.]
> Signed-off-by: John Hubbard <[email protected]>
Makes sence. Feel free to add:
Reviewed-by: Jan Kara <[email protected]>
Honza
> ---
> mm/gup.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index a9d4d724aef7..80229ecf0114 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -465,7 +465,7 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
> pte_t *pte, unsigned int flags)
> {
> /* No page to get reference */
> - if (flags & FOLL_GET)
> + if (flags & (FOLL_GET | FOLL_PIN))
> return -EFAULT;
>
> if (flags & FOLL_TOUCH) {
> --
> 2.35.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
On 2/3/22 23:25, Christoph Hellwig wrote:
> On Thu, Feb 03, 2022 at 06:00:06PM -0800, John Hubbard wrote:
>> From: Peter Xu <[email protected]>
>>
>> Alex reported invalid page pointer returned with pin_user_pages_remote() from
>> vfio after upstream commit 4b6c33b32296 ("vfio/type1: Prepare for batched
>> pinning with struct vfio_batch").
>
> This commit message uses overly long lines all over.
I'll reflow it to 72 columns and post a v5 with the full set of
reviewed-by tags.
>
> Otherwise looks good:
>
> Reviewed-by: Christoph Hellwig <[email protected]>
I appreciate the reviews, from you and everyone, as always.
thanks,
--
John Hubbard
NVIDIA