xen/gntdev.c: Replace vm_map_pages() with vm_map_pages_zero()
'commitdf9bde015a
("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@vger.kernel.org # v5.2+ Fixes:df9bde015a
("xen/gntdev.c: convert to use vm_map_pages()") Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Juergen Gross <jgross@suse.com>
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@ -1143,7 +1143,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
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goto out_put_map;
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if (!use_ptemod) {
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err = vm_map_pages(vma, map->pages, map->count);
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err = vm_map_pages_zero(vma, map->pages, map->count);
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if (err)
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goto out_put_map;
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} else {
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