linux-kernel - Re: [PATCH v2 2/4] kasan: use MAX_PTRS_PER

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Message-ID: <de333171-6697-aabc-70da-c9d593adfb08@c-s.fr>
Date:   Tue, 10 Dec 2019 07:40:09 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kasan-dev@...glegroups.com, aneesh.kumar@...ux.ibm.com,
        bsingharora@...il.com
Subject: Re: [PATCH v2 2/4] kasan: use MAX_PTRS_PER_* for early shadow



Le 10/12/2019 à 05:47, Daniel Axtens a écrit :
> This helps with powerpc support, and should have no effect on
> anything else.

As explained in previous patch, this patch is based on MAX_PTRS_PER_Pxx 
existing for every arch using KASAN, allthought all arches but powerpc 
will define it as PTRS_PER_Pxx.

I think instead of forcing all arches to define that value, just define 
a fallback in kasan.h (or somewhere else) would help keeping the changes 
to the minimum, see below.

> 
> Suggested-by: Christophe Leroy <christophe.leroy@....fr>
> Signed-off-by: Daniel Axtens <dja@...ens.net>
> ---
>   include/linux/kasan.h | 6 +++---
>   mm/kasan/init.c       | 6 +++---
>   2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index e18fe54969e9..d2f2a4ffcb12 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -15,9 +15,9 @@ struct task_struct;
>   #include <asm/pgtable.h>

Add

#ifndef MAX_PTRS_PER_PTE
#define MAX_PTRS_PER_PTE PTRS_PER_PTE
#endif

#ifndef MAX_PTRS_PER_PMD
#define MAX_PTRS_PER_PMD PTRS_PER_PMD
#endif

#ifndef MAX_PTRS_PER_PUD
#define MAX_PTRS_PER_PUD PTRS_PER_PUD
#endif

#ifndef MAX_PTRS_PER_P4D
#define MAX_PTRS_PER_P4D PTRS_PER_P4D
#endif

With that you don't need patch 1.

>   
>   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];
> -extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
> +extern pte_t kasan_early_shadow_pte[MAX_PTRS_PER_PTE];
> +extern pmd_t kasan_early_shadow_pmd[MAX_PTRS_PER_PMD];
> +extern pud_t kasan_early_shadow_pud[MAX_PTRS_PER_PUD];
>   extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>   
>   int kasan_populate_early_shadow(const void *shadow_start,
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index ce45c491ebcd..8b54a96d3b3e 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -46,7 +46,7 @@ static inline bool kasan_p4d_table(pgd_t pgd)
>   }
>   #endif
>   #if CONFIG_PGTABLE_LEVELS > 3
> -pud_t kasan_early_shadow_pud[PTRS_PER_PUD] __page_aligned_bss;
> +pud_t kasan_early_shadow_pud[MAX_PTRS_PER_PUD] __page_aligned_bss;
>   static inline bool kasan_pud_table(p4d_t p4d)
>   {
>   	return p4d_page(p4d) == virt_to_page(lm_alias(kasan_early_shadow_pud));
> @@ -58,7 +58,7 @@ static inline bool kasan_pud_table(p4d_t p4d)
>   }
>   #endif
>   #if CONFIG_PGTABLE_LEVELS > 2
> -pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +pmd_t kasan_early_shadow_pmd[MAX_PTRS_PER_PMD] __page_aligned_bss;
>   static inline bool kasan_pmd_table(pud_t pud)
>   {
>   	return pud_page(pud) == virt_to_page(lm_alias(kasan_early_shadow_pmd));
> @@ -69,7 +69,7 @@ static inline bool kasan_pmd_table(pud_t pud)
>   	return false;
>   }
>   #endif
> -pte_t kasan_early_shadow_pte[PTRS_PER_PTE] __page_aligned_bss;
> +pte_t kasan_early_shadow_pte[MAX_PTRS_PER_PTE] __page_aligned_bss;
>   
>   static inline bool kasan_pte_table(pmd_t pmd)
>   {
> 

Christophe