[PATCH 5.2 119/131] xen/gntdev.c: Replace vm_map_pages() with vm_map_pages_zero()
From: Greg Kroah-Hartman
Date: Mon Aug 05 2019 - 09:27:03 EST
From: Souptick Joarder <jrdr.linux@xxxxxxxxx>
commit 8d1502f629c9966743de45744f4c1ba93a57d105 upstream.
'commit df9bde015a72 ("xen/gntdev.c: convert to use vm_map_pages()")'
breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_pages()
will:
- use map->pages starting at vma->vm_pgoff instead of 0
- verify map->count against vma_pages()+vma->vm_pgoff instead of just
vma_pages().
In practice, this breaks using a single gntdev FD for mapping multiple
grants.
relevant strace output:
[pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0
[pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7, 0) =
0x777f1211b000
[pid 857] ioctl(7, IOCTL_GNTDEV_SET_UNMAP_NOTIFY, 0x7ffd3407b710) = 0
[pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0
[pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7,
0x1000) = -1 ENXIO (No such device or address)
details here:
https://github.com/QubesOS/qubes-issues/issues/5199
The reason is -> ( copying Marek's word from discussion)
vma->vm_pgoff is used as index passed to gntdev_find_map_index. It's
basically using this parameter for "which grant reference to map".
map struct returned by gntdev_find_map_index() describes just the pages
to be mapped. Specifically map->pages[0] should be mapped at
vma->vm_start, not vma->vm_start+vma->vm_pgoff*PAGE_SIZE.
When trying to map grant with index (aka vma->vm_pgoff) > 1,
__vm_map_pages() will refuse to map it because it will expect map->count
to be at least vma_pages(vma)+vma->vm_pgoff, while it is exactly
vma_pages(vma).
Converting vm_map_pages() to use vm_map_pages_zero() will fix the
problem.
Marek has tested and confirmed the same.
Cc: stable@xxxxxxxxxxxxxxx # v5.2+
Fixes: df9bde015a72 ("xen/gntdev.c: convert to use vm_map_pages()")
Reported-by: Marek Marczykowski-GÃrecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Tested-by: Marek Marczykowski-GÃrecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/xen/gntdev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -1145,7 +1145,7 @@ static int gntdev_mmap(struct file *flip
goto out_put_map;
if (!use_ptemod) {
- err = vm_map_pages(vma, map->pages, map->count);
+ err = vm_map_pages_zero(vma, map->pages, map->count);
if (err)
goto out_put_map;
} else {