[RFC PATCH 3/5] kasan: allow architectures to provide an outline readiness check

[christophe leroy]

Le 15/02/2019 à 01:04, Daniel Axtens a écrit :
> In powerpc (as I understand it), we spend a lot of time in boot
> running in real mode before MMU paging is initalised. During
> this time we call a lot of generic code, including printk(). If
> we try to access the shadow region during this time, things fail.
> 
> My attempts to move early init before the first printk have not
> been successful. (Both previous RFCs for ppc64 - by 2 different
> people - have needed this trick too!)
> 
> So, allow architectures to define a check_return_arch_not_ready()
> hook that bails out of check_memory_region_inline() unless the
> arch has done all of the init.
> 
> Link: https://lore.kernel.org/patchwork/patch/592820/ # ppc64 hash series
> Link: https://patchwork.ozlabs.org/patch/795211/      # ppc radix series
> Originally-by: Balbir Singh <bsingharora at gmail.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> Signed-off-by: Daniel Axtens <dja at axtens.net>
> ---
>   include/linux/kasan.h | 4 ++++
>   mm/kasan/generic.c    | 2 ++
>   2 files changed, 6 insertions(+)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index f6261840f94c..83edc5e2b6a0 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -14,6 +14,10 @@ struct task_struct;
>   #include <asm/kasan.h>
>   #include <asm/pgtable.h>
>   
> +#ifndef check_return_arch_not_ready
> +#define check_return_arch_not_ready()	do { } while (0)
> +#endif

A static inline would be better I believe.

Something like

#ifndef kasan_arch_is_ready
static inline bool kasan_arch_is_ready {return true;}
#endif

> +
>   extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
>   extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
>   extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index bafa2f986660..4c18bbd09a20 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -170,6 +170,8 @@ static __always_inline void check_memory_region_inline(unsigned long addr,
>   						size_t size, bool write,
>   						unsigned long ret_ip)
>   {
> +	check_return_arch_not_ready();
> +

Not good for readibility that the above macro embeds a return, something 
like below would be better I think:

	if (!kasan_arch_is_ready())
		return;

Unless somebody minds, I'll do the change and take this patch in my 
series in order to handle the case of book3s/32 hash.

Christophe

>   	if (unlikely(size == 0))
>   		return;
>   
> 

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