Re: [PATCH v14 3/9] powerpc/modules: Make module_alloc() Strict Module RWX aware

[Jordan Niethe <jniethe5@gmail.com>]

On Mon, May 17, 2021 at 4:37 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 17/05/2021 à 05:28, Jordan Niethe a écrit :
> > Make module_alloc() use PAGE_KERNEL protections instead of
> > PAGE_KERNEL_EXEX if Strict Module RWX is enabled.
> >
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> > v14: - Split out from powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
> >       - Add and use strict_module_rwx_enabled() helper
> > ---
> >   arch/powerpc/include/asm/mmu.h | 5 +++++
> >   arch/powerpc/kernel/module.c   | 4 +++-
> >   2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> > index 607168b1aef4..7710bf0cbf8a 100644
> > --- a/arch/powerpc/include/asm/mmu.h
> > +++ b/arch/powerpc/include/asm/mmu.h
> > @@ -357,6 +357,11 @@ static inline bool strict_kernel_rwx_enabled(void)
> >       return false;
> >   }
> >   #endif
> > +
> > +static inline bool strict_module_rwx_enabled(void)
> > +{
> > +     return IS_ENABLED(CONFIG_STRICT_MODULE_RWX) && strict_kernel_rwx_enabled();
> > +}
>
> Looking at arch/Kconfig, I have the feeling that it is possible to select CONFIG_STRICT_MODULE_RWX
> without selecting CONFIG_STRICT_KERNEL_RWX.
>
> In that case, strict_kernel_rwx_enabled() will return false.
Ok, if someone did that currently it would break things, e.g. code
patching. I think it should it be made impossible to
CONFIG_STRICT_MODULE_RWX without CONFIG_STRICT_KERNEL_RWX?
>
> >   #endif /* !__ASSEMBLY__ */
> >
> >   /* The kernel use the constants below to index in the page sizes array.
> > diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> > index 3f35c8d20be7..ed04a3ba66fe 100644
> > --- a/arch/powerpc/kernel/module.c
> > +++ b/arch/powerpc/kernel/module.c
> > @@ -92,12 +92,14 @@ int module_finalize(const Elf_Ehdr *hdr,
> >   static __always_inline void *
> >   __module_alloc(unsigned long size, unsigned long start, unsigned long end)
> >   {
> > +     pgprot_t prot = strict_module_rwx_enabled() ? PAGE_KERNEL : PAGE_KERNEL_EXEC;
> > +
> >       /*
> >        * Don't do huge page allocations for modules yet until more testing
> >        * is done. STRICT_MODULE_RWX may require extra work to support this
> >        * too.
> >        */
> > -     return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL, PAGE_KERNEL_EXEC,
> > +     return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL, prot,
> >                                   VM_FLUSH_RESET_PERMS | VM_NO_HUGE_VMAP,
> >                                   NUMA_NO_NODE, __builtin_return_address(0));
> >   }
> >