[PATCH 1/4] kasan: allow arches to provide their own early shadow setup

[Christophe Leroy]

Le 07/08/2019 à 17:14, Christophe Leroy a écrit :
> 
> 
> 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 ?

To illustrate my suggestion, see commit c65e774fb3f6af21 ("x86/mm: Make 
PGDIR_SHIFT and PTRS_PER_P4D variable")

The same principle should apply on all variable powerpc PTRS_PER_XXX.

Christophe

> 
> 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 at 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)
>>   {
>>