Re: [PATCH] kernel: sys: fix potential Spectre v1

[Gustavo A. R. Silva]

On 05/23/2018 12:15 AM, Dan Williams wrote:
> > OK. How about this:
> >
> > diff --git a/include/linux/nospec.h b/include/linux/nospec.h
> > index e791ebc..498995b 100644
> > --- a/include/linux/nospec.h
> > +++ b/include/linux/nospec.h
> > @@ -55,4 +55,21 @@ static inline unsigned long
> > array_index_mask_nospec(unsigned long index,
> >                                                                         \
> >          (typeof(_i)) (_i & _mask);                                     \
> >   })
> > +
> > +#define validate_index_nospec(index, size)                            \
> > +({                                                                    \
> > +       bool ret = true;                                               \
> > +       typeof(index) *ptr = &(index);                                 \
> > +       typeof(size) _s = (size);                                      \
> > +                                                                      \
> > +       BUILD_BUG_ON(sizeof(*ptr) > sizeof(long));                     \
> > +       BUILD_BUG_ON(sizeof(_s) > sizeof(long));                       \
> > +                                                                      \
> > +       if (*ptr >= size)                                              \

I'll change the line above by this one:

if (*ptr >= _s)

> > +               ret = false;                                           \
> > +                                                                      \
> > +       *ptr = array_index_nospec(*ptr, _s);                           \
> > +                                                                      \
> > +       ret;                                                           \
> >
> > +})
> >   #endif /* _LINUX_NOSPEC_H */
>
> Assuming the assembly generation is comparable with the open coded
> version, this looks ok to me.

OK. I'll send a proper patch tomorrow morning.

Thanks for the feedback, Dan.
--
Gustavo