Re: [PATCH] modules: fix compile error if don't have strict module rwx

[Yang Yingliang]

On 2019/6/26 3:21, Jessica Yu wrote:
> +++ Yang Yingliang [25/06/19 17:40 +0800]:
> > If CONFIG_ARCH_HAS_STRICT_MODULE_RWX is not defined,
> > we need stub for module_enable_nx() and module_enable_x().
> >
> > If CONFIG_ARCH_HAS_STRICT_MODULE_RWX is defined, but
> > CONFIG_STRICT_MODULE_RWX is disabled, we need stub for
> > module_enable_nx.
> >
> > Move frob_text() outside of the CONFIG_STRICT_MODULE_RWX,
> > because it is needed anyway.
>
> Maybe include a fixes tag?
>
> Fixes: 2eef1399a866 ("modules: fix BUG when load module with rodata=n")
OK, I will add it in v2.
> > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > ---
> > kernel/module.c | 13 +++++++++----
> > 1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index c3ae34c..cfff441 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -1875,7 +1875,7 @@ static void mod_sysfs_teardown(struct module *mod)
> >     mod_sysfs_fini(mod);
> > }
> >
> > -#ifdef CONFIG_STRICT_MODULE_RWX
> > +#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
>
> Could you please explain why you introduced a new
> CONFIG_ARCH_HAS_STRICT_MODULE_RWX #ifdef block instead of just moving
> frob_text() and module_enable_x() outside of CONFIG_STRICT_MODULE_RWX?
If CONFIG_STRICT_MODULE_RWX is not defined, it has two reasons, one is 
that the
arch don't have strict module rwx and the other reason is that 
CONFIG_STRICT_MODULE_RWX
is disabled. So I introduce CONFIG_ARCH_HAS_STRICT_MODULE_RWX #ifdef 
block to
distinguish this two cases.

> I do not have anything against it, although the nested #ifdef's are a
> bit painful to read. But I could not find a better way to do it :/
> It's awkward because we need module_enable_x() and frob_text()
> regardless of of CONFIG_STRICT_MODULE_RWX for x86, but other arches
> don't need to call module_enable_x(), they usually just call the empty 
> stub.
Yes, you are right.
Actually, I was thinking moving all frob_* outside of 
CONFIG_STRICT_MODULE_RWX,
because they all should be regardless of of CONFIG_STRICT_MODULE_RWX. 
But current
only frob_next() is used, move other frob_* outside of 
CONFIG_STRICT_MODULE_RWX
will cause a compile warning if CONFIG_STRICT_MODULE_RWX is disabled, so 
I left them
in CONFIG_STRICT_MODULE_RWX.  We can move them outside of 
CONFIG_STRICT_MODULE_RWX
if they are used in future.
> But I think having the CONFIG_ARCH_HAS_STRICT_MODULE_RWX block is OK,
> for the reason of limiting the scope of the calls rather than
> blanketly calling frob_text() andd module_enable_x() for arches that
> don't need to call them. Was that your reasoning as well?
Yes,  it's my reasoning.


Thanks,
Yang
> Thanks,
>
> Jessica
>
>
> > /*
> >  * LKM RO/NX protection: protect module's text/ro-data
> >  * from modification and any data from execution.
> > @@ -1898,6 +1898,7 @@ static void frob_text(const struct 
> > module_layout *layout,
> >            layout->text_size >> PAGE_SHIFT);
> > }
> >
> > +#ifdef CONFIG_STRICT_MODULE_RWX
> > static void frob_rodata(const struct module_layout *layout,
> >             int (*set_memory)(unsigned long start, int num_pages))
> > {
> > @@ -2010,15 +2011,19 @@ void set_all_modules_text_ro(void)
> >     }
> >     mutex_unlock(&module_mutex);
> > }
> > -#else
> > +#else /* !CONFIG_STRICT_MODULE_RWX */
> > static void module_enable_nx(const struct module *mod) { }
> > -#endif
> > -
> > +#endif /*  CONFIG_STRICT_MODULE_RWX */
> > static void module_enable_x(const struct module *mod)
> > {
> >     frob_text(&mod->core_layout, set_memory_x);
> >     frob_text(&mod->init_layout, set_memory_x);
> > }
> > +#else /* !CONFIG_ARCH_HAS_STRICT_MODULE_RWX */
> > +static void module_enable_nx(const struct module *mod) { }
> > +static void module_enable_x(const struct module *mod) { }
> > +#endif /* CONFIG_ARCH_HAS_STRICT_MODULE_RWX */
> > +
> >
> > #ifdef CONFIG_LIVEPATCH
> > /*
> > --
> > 1.8.3
>
> .