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SubjectRe: [PATCH repost 12/16] parisc/uaccess: fix sparse errors
On Thu, Dec 25, 2014 at 11:37:45PM +0100, Helge Deller wrote:
> Hi Michael,
>
> On 12/25/2014 10:29 AM, Michael S. Tsirkin wrote:
> >virtio wants to read bitwise types from userspace using get_user. At the
>
> I don't know the virtio code much yet, but does it makes sense to read bitwise types?
> Will virtio then get possible troubles because of endianess correct as well?

There's no conversion: we are reading from __virtio16 __user *
pointer into __virtio16 v value.

> Do you have a code example, or the sparse error message ?
>
> Helge

Sure. the code is upstream now.
The warning is below.

sparse warnings: (new ones prefixed by >>)

>> drivers/vhost/vringh.c:554:18: sparse: cast to restricted __virtio16

vim +554 drivers/vhost/vringh.c

538 __virtio16 *p, u16 val))
539 {
540 if (!vrh->event_indices) {
541 /* Old-school; update flags. */
542 if (putu16(vrh, &vrh->vring.used->flags,
543 VRING_USED_F_NO_NOTIFY)) {
544 vringh_bad("Setting used flags %p",
545 &vrh->vring.used->flags);
546 }
547 }
548 }
549
550 /* Userspace access helpers: in this case, addresses are really userspace. */
551 static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)
552 {
553 __virtio16 v = 0;
> 554 int rc = get_user(v, (__force __virtio16 __user *)p);
555 *val = vringh16_to_cpu(vrh, v);
556 return rc;
557 }
558
559 static inline int putu16_user(const struct vringh *vrh, __virtio16 *p, u16 val)
560 {
561 __virtio16 v = cpu_to_vringh16(vrh, val);
562 return put_user(v, (__force __virtio16 __user *)p);



>
> >moment this triggers sparse errors, since the value is passed through an
> >integer.
> >
> >Fix that up using __force.
> >
> >Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> >---
> > arch/parisc/include/asm/uaccess.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
> >index a5cb070..3a20da6 100644
> >--- a/arch/parisc/include/asm/uaccess.h
> >+++ b/arch/parisc/include/asm/uaccess.h
> >@@ -104,7 +104,7 @@ struct exception_data {
> > } \
> > } \
> > \
> >- (x) = (__typeof__(*(ptr))) __gu_val; \
> >+ (x) = (__force __typeof__(*(ptr))) __gu_val; \
> > __gu_err; \
> > })
> >
> >


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