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Subject: Re: [PATCH 1/4] kasan: allow arches to provide their own early shadow
 setup
To: Daniel Axtens <dja@axtens.net>, aneesh.kumar@linux.ibm.com,
 bsingharora@gmail.com
References: <20190806233827.16454-1-dja@axtens.net>
 <20190806233827.16454-2-dja@axtens.net>
From: Christophe Leroy <christophe.leroy@c-s.fr>
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Date: Wed, 7 Aug 2019 17:14:03 +0200
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Le 07/08/2019 à 01:38, Daniel Axtens a écrit :
> powerpc supports several different MMUs. In particular, book3s
> machines support both a hash-table based MMU and a radix MMU.
> These MMUs support different numbers of entries per directory
> level: the PTES_PER_* defines evaluate to variables, not constants.
> This leads to complier errors as global variables must have constant
> sizes.
> 
> Allow architectures to manage their own early shadow variables so we
> can work around this on powerpc.

This seems rather strange to move the early shadow tables out of 
mm/kasan/init.c allthough they are used there still.

What about doing for all what is already done for 
kasan_early_shadow_p4d[], in extenso define constant max sizes 
MAX_PTRS_PER_PTE, MAX_PTRS_PER_PMD and MAX_PTRS_PER_PUD ?

With a set of the following, it would remain transparent for other arches.
#ifndef MAX_PTRS_PER_PXX
#define MAX_PTRS_PER_PXX PTRS_PER_PXX
#endif

Then you would just need to do the following for Radix:

#define MAX_PTRS_PER_PTE		(1 << RADIX_PTE_INDEX_SIZE)
#define MAX_PTRS_PER_PMD		(1 << RADIX_PMD_INDEX_SIZE)
#define MAX_PTRS_PER_PUD		(1 << RADIX_PUD_INDEX_SIZE)


For the kasan_early_shadow_page[], I don't think we have variable 
PAGE_SIZE, have we ?

Christophe


> 
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> 
> ---
> Changes from RFC:
> 
>   - To make checkpatch happy, move ARCH_HAS_KASAN_EARLY_SHADOW from
>     a random #define to a config option selected when building for
>     ppc64 book3s
> ---
>   include/linux/kasan.h |  2 ++
>   lib/Kconfig.kasan     |  3 +++
>   mm/kasan/init.c       | 10 ++++++++++
>   3 files changed, 15 insertions(+)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index ec81113fcee4..15933da52a3e 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -14,11 +14,13 @@ struct task_struct;
>   #include <asm/kasan.h>
>   #include <asm/pgtable.h>
>   
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   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 p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
> +#endif
>   
>   int kasan_populate_early_shadow(const void *shadow_start,
>   				const void *shadow_end);
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index a320dc2e9317..0621a0129c04 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -9,6 +9,9 @@ config HAVE_ARCH_KASAN_SW_TAGS
>   config	HAVE_ARCH_KASAN_VMALLOC
>   	bool
>   
> +config ARCH_HAS_KASAN_EARLY_SHADOW
> +	bool
> +
>   config CC_HAS_KASAN_GENERIC
>   	def_bool $(cc-option, -fsanitize=kernel-address)
>   
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index ce45c491ebcd..7ef2b87a7988 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -31,10 +31,14 @@
>    *   - Latter it reused it as zero shadow to cover large ranges of memory
>    *     that allowed to access, but not handled by kasan (vmalloc/vmemmap ...).
>    */
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   unsigned char kasan_early_shadow_page[PAGE_SIZE] __page_aligned_bss;
> +#endif
>   
>   #if CONFIG_PGTABLE_LEVELS > 4
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D] __page_aligned_bss;
> +#endif
>   static inline bool kasan_p4d_table(pgd_t pgd)
>   {
>   	return pgd_page(pgd) == virt_to_page(lm_alias(kasan_early_shadow_p4d));
> @@ -46,7 +50,9 @@ static inline bool kasan_p4d_table(pgd_t pgd)
>   }
>   #endif
>   #if CONFIG_PGTABLE_LEVELS > 3
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   pud_t kasan_early_shadow_pud[PTRS_PER_PUD] __page_aligned_bss;
> +#endif
>   static inline bool kasan_pud_table(p4d_t p4d)
>   {
>   	return p4d_page(p4d) == virt_to_page(lm_alias(kasan_early_shadow_pud));
> @@ -58,7 +64,9 @@ static inline bool kasan_pud_table(p4d_t p4d)
>   }
>   #endif
>   #if CONFIG_PGTABLE_LEVELS > 2
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +#endif
>   static inline bool kasan_pmd_table(pud_t pud)
>   {
>   	return pud_page(pud) == virt_to_page(lm_alias(kasan_early_shadow_pmd));
> @@ -69,7 +77,9 @@ static inline bool kasan_pmd_table(pud_t pud)
>   	return false;
>   }
>   #endif
> +#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
>   pte_t kasan_early_shadow_pte[PTRS_PER_PTE] __page_aligned_bss;
> +#endif
>   
>   static inline bool kasan_pte_table(pmd_t pmd)
>   {
>