On 07/06/18 11:21, Paul Durrant wrote:
> Commit 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
> introduced a static checker warning:
>
> drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
> warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
> 64 vs 32.
>
> caused by this cast:
>
> 827 num = xen_remap_domain_mfn_array(vma,
> 828 kdata.addr & PAGE_MASK,
> 829 pfns, kdata.num, (int *)pfns,
> ^^^^^^^^^^^
>
> The reason for the cast is that xen_remap_domain_mfn_array() requires an
> array of ints to store error codes. It is actually safe to re-use the
> pfns array for this purpose but it does look odd (as well as leading to
> the warning). It would also be easy for a future implementation change
> to make this re-use unsafe so this patch modifies privcmd to use a
> separately allocated array for error codes.
>
> Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
> Signed-off-by: Paul Durrant <paul.durr...@citrix.com>
It may be safe to reuse pfns[] as the storage space for the errs array,
but code is incorrect when sizeof(pfn) != sizeof(int). In such a case,
you skip over every other err, and second half of pfns[] is junk from
the point of view of the errs loop.
~Andrew
> ---
> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
> Cc: Juergen Gross <jgr...@suse.com>
> Cc: Dan Carpenter <dan.carpen...@oracle.com>
> ---
> drivers/xen/privcmd.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 8ae0349..8507c13 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -822,11 +822,18 @@ static long privcmd_ioctl_mmap_resource(struct file
> *file, void __user *udata)
> unsigned int domid =
> (xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
> DOMID_SELF : kdata.dom;
> + int *errs;
> int num;
>
> + errs = kcalloc(kdata.num, sizeof(*errs), GFP_KERNEL);
> + if (!errs) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> num = xen_remap_domain_mfn_array(vma,
> kdata.addr & PAGE_MASK,
> - pfns, kdata.num, (int *)pfns,
> + pfns, kdata.num, errs,
> vma->vm_page_prot,
> domid,
> vma->vm_private_data);
> @@ -836,12 +843,14 @@ static long privcmd_ioctl_mmap_resource(struct file
> *file, void __user *udata)
> unsigned int i;
>
> for (i = 0; i < num; i++) {
> - rc = pfns[i];
> + rc = errs[i];
> if (rc < 0)
> break;
> }
> } else
> rc = 0;
> +
> + kfree(errs);
> }
>
> out:
