[RFC PATCH 6/7] kasan: allow arches to hook into global registration

[Christophe Leroy]

Le 23/05/2019 à 07:21, Daniel Axtens a écrit :
> Not all arches have a specific space carved out for modules -
> some, such as powerpc, just use regular vmalloc space. Therefore,
> globals in these modules cannot be backed by real shadow memory.

Can you explain in more details the reason why ?

PPC32 also uses regular vmalloc space, and it has been possible to 
manage globals on it, by simply implementing a module_alloc() function.

See 
https://elixir.bootlin.com/linux/v5.2-rc1/source/arch/powerpc/mm/kasan/kasan_init_32.c#L135

It is also possible to easily define a different area for modules, by 
replacing the call to vmalloc_exec() by a call to __vmalloc_node_range() 
as done by vmalloc_exec(), but with different bounds than 
VMALLOC_START/VMALLOC_END

See https://elixir.bootlin.com/linux/v5.2-rc1/source/mm/vmalloc.c#L2633

Today in PPC64 (unlike PPC32), there is already a split between VMALLOC 
space and IOREMAP space. I'm sure it would be easy to split it once more 
for modules.

Christophe

> 
> In order to allow arches to perform this check, add a hook.
> 
> Signed-off-by: Daniel Axtens <dja at axtens.net>
> ---
>   include/linux/kasan.h | 5 +++++
>   mm/kasan/generic.c    | 3 +++
>   2 files changed, 8 insertions(+)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index dfee2b42d799..4752749e4797 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -18,6 +18,11 @@ struct task_struct;
>   static inline bool kasan_arch_is_ready(void)	{ return true; }
>   #endif
>   
> +#ifndef kasan_arch_can_register_global
> +static inline bool kasan_arch_can_register_global(const void * addr)	{ return true; }
> +#endif
> +
> +
>   #ifndef ARCH_HAS_KASAN_EARLY_SHADOW
>   extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
>   extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 0336f31bbae3..935b06f659a0 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -208,6 +208,9 @@ static void register_global(struct kasan_global *global)
>   {
>   	size_t aligned_size = round_up(global->size, KASAN_SHADOW_SCALE_SIZE);
>   
> +	if (!kasan_arch_can_register_global(global->beg))
> +		return;
> +
>   	kasan_unpoison_shadow(global->beg, global->size);
>   
>   	kasan_poison_shadow(global->beg + aligned_size,
>