Re: [PATCH 03/18] arm64/uaccess: fix sparse errors

Russell King - ARM Linux
2014-12-15T11:23:22Z

On Mon, Dec 15, 2014 at 11:17:16AM +0000, Will Deacon wrote:
> On Sun, Dec 14, 2014 at 04:52:09PM +0000, Michael S. Tsirkin wrote:
> > virtio wants to read bitwise types from userspace using get_user. At the
> > 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/arm64/include/asm/uaccess.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > index 3bf8f4e..8d66bcf 100644
> > --- a/arch/arm64/include/asm/uaccess.h
> > +++ b/arch/arm64/include/asm/uaccess.h
> > @@ -147,7 +147,7 @@ do { \
> > default: \
> > BUILD_BUG(); \
> > } \
> > - (x) = (__typeof__(*(ptr)))__gu_val; \
> > + (x) = (__force __typeof__(*(ptr)))__gu_val; \
> > } while (0)
> >
> > #define __get_user(x, ptr) \
>
> Acked-by: Will Deacon <will.deacon@arm.com>

This also means you can do stuff like:

u32 *p;
__le32 v;

err = get_user(p, v);

which is not right. Both the dereferenced pointer type and the destination
type should be compatible, and if one is a bitwise type but the other isn't,
that seems like a valid case to warn.

I don't see any use of get_user() in drivers/virtio in mainline, so I can't
check further.

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