[PATCH 2/3] powerpc: Fix undefined static key

[Joel Stanley]

On Mon, 16 Aug 2021 at 08:39, Christophe Leroy
<christophe.leroy at csgroup.eu> wrote:
>
>
>
> Le 16/08/2021 à 10:24, Joel Stanley a écrit :
> > When CONFIG_PPC_BARRIER_NOSPEC=n, security.c is not built leading to a
> > missing definition of uaccess_flush_key.
> >
> >    LD      vmlinux.o
> >    MODPOST vmlinux.symvers
> >    MODINFO modules.builtin.modinfo
> >    GEN     modules.builtin
> >    LD      .tmp_vmlinux.kallsyms1
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/align.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/signal_64.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/process.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/traps.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/hw_breakpoint_constraints.o:(.toc+0x0): undefined reference to `uaccess_flush_key'
> > powerpc64le-linux-gnu-ld: arch/powerpc/kernel/ptrace/ptrace.o:(.toc+0x0): more undefined references to `uaccess_flush_key' follow
> > make[1]: *** [Makefile:1176: vmlinux] Error 1
> >
> > Hack one in to fix the build.
> >
> > Signed-off-by: Joel Stanley <joel at jms.id.au>
> > ---
> >   arch/powerpc/include/asm/security_features.h | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/powerpc/include/asm/security_features.h b/arch/powerpc/include/asm/security_features.h
> > index 792eefaf230b..46ade7927a4c 100644
> > --- a/arch/powerpc/include/asm/security_features.h
> > +++ b/arch/powerpc/include/asm/security_features.h
> > @@ -39,6 +39,9 @@ static inline bool security_ftr_enabled(u64 feature)
> >       return !!(powerpc_security_features & feature);
> >   }
> >
> > +#ifndef CONFIG_PPC_BARRIER_NOSPEC
> > +DEFINE_STATIC_KEY_FALSE(uaccess_flush_key);
> > +#endif
>
> It will then be re-defined by each file that includes asm/security_features.h ....
>
> You can't use a DEFINE_ in a .h
>
> You have to fix the problem at its source.
>
> Cleanest way I see it to modify asm/book3s/64/kup.h and something like
>
> if (IS_ENABLED(CONFIG_PPC_BARRIER_NOSPEC) && static_branch_unlikely(&uaccess_flush_key)

This won't work either as there's no declaration for uaccess_flush_key:

arch/powerpc/include/asm/book3s/64/kup.h:411:78: error:
‘uaccess_flush_key’ undeclared (first use in this function)

We could add an extern for it, but that is distasteful as the static
key API suggests using the structs directly is deprecated, and the
macros we're supposed to use perform initialisation.

Could we assume microwatt-like platforms will not gain pkeys support,
and have a stubbed out set of prevent/restore_user_access for systems
that turn off either pkeys or BARRIER_NOSPEC?

Or do we get rid of PPC_BARRIER_NOSPEC as an option, and have machines
rely on disabling it at runtime?