On Fri, Mar 08, 2019 at 01:00:38PM -0600, Josh Poimboeuf wrote:
> On Thu, Mar 07, 2019 at 12:45:16PM +0100, Peter Zijlstra wrote:
> > drivers/xen/privcmd.o: warning: objtool: privcmd_ioctl()+0x1414: call to
> > hypercall_page() with UACCESS enabled
> >
> > Xen needs to do HV calls with AC=1 for hysterical raisins. Make the
> > warning go away.
> >
> > XXX: arguably we should rename ANNOTATE_NOSPEC_ALTERNATIVE to
> > ANNOTATE_IGNORE_ALTERNATIVE.
> >
> > Cc: andrew.coop...@citrix.com
> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> > ---
> > arch/x86/include/asm/xen/hypercall.h | 26 ++++++++++++++++++++++----
> > 1 file changed, 22 insertions(+), 4 deletions(-)
> >
> > --- a/arch/x86/include/asm/xen/hypercall.h
> > +++ b/arch/x86/include/asm/xen/hypercall.h
> > @@ -214,6 +214,24 @@ xen_single_call(unsigned int call,
> > return (long)__res;
> > }
> >
> > +static __always_inline void __xen_stac(void)
> > +{
> > + /*
> > + * This is just about as horrible as this interface; we abuse the
> > + * nospec alternative annotation to supress objtool seeing the
> > + * STAC/CLAC and getting confused about it calling random code with
> > + * AC=1.
> > + */
> > + asm volatile(ANNOTATE_NOSPEC_ALTERNATIVE
> > + ASM_STAC ::: "memory", "flags");
> > +}
> > +
> > +static __always_inline void __xen_clac(void)
> > +{
> > + asm volatile(ANNOTATE_NOSPEC_ALTERNATIVE
> > + ASM_CLAC ::: "memory", "flags");
> > +}
> > +
>
> Shouldn't these be using SMAP-based alternatives like stac()/clac() do?
Also this you could get rid of the comment if there were an
ANNOTATE_AC_SAFE macro which does a similar thing.
--
Josh
