On 2025-02-06 at 00:45:01 +0100, Andrey Konovalov wrote:
>On Tue, Feb 4, 2025 at 6:35 PM Maciej Wieczor-Retman
><maciej.wieczor-retman@xxxxxxxxx> wrote:
>>
>> In KASAN's tag-based mode (arm64) when a memory access occurs, the tag
>> stored in the top 8 bits of the pointer is compared with tags saved in
>> the region of the shadow memory that maps to memory the pointer points
>> to. If any of the tags in the shadow memory region do not match the one
>> stored in the pointer an error report is generated.
>>
>> With the introduction of the dense mode, tags won't necessarily occupy
>> whole bytes of shadow memory if the previously allocated memory wasn't
>> aligned to 32 bytes - which is the coverage of one shadow byte.
>>
>> Add an alternative implementation of kasan_check_range() that performs
>> special checks on first and last bytes of shadow memory ranges if the
>> originally allocated memory wasn't aligned to 32 bytes.
>>
>> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
>> ---
>> include/linux/kasan.h | 47 +++++++++++++++-------
>> mm/kasan/Makefile | 3 ++
>> mm/kasan/dense.c | 83 +++++++++++++++++++++++++++++++++++++++
>> mm/kasan/kasan.h | 2 +-
>> mm/kasan/report.c | 2 +-
>> mm/kasan/report_sw_tags.c | 12 ++----
>> mm/kasan/sw_tags.c | 8 ++++
>> 7 files changed, 133 insertions(+), 24 deletions(-)
>> create mode 100644 mm/kasan/dense.c
>>
>> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
>> index ea0f5acd875b..5a3e9bec21c2 100644
>> --- a/include/linux/kasan.h
>> +++ b/include/linux/kasan.h
>> @@ -33,6 +33,20 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t;
>>
>> #include <linux/pgtable.h>
>>
>> +#ifndef kasan_mem_to_shadow
>> +static inline void *kasan_mem_to_shadow(const void *addr)
>> +{
>> + void *scaled;
>> +
>> + if (IS_ENABLED(CONFIG_KASAN_GENERIC))
>> + scaled = (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT);
>> + else
>> + scaled = (void *)((long)addr >> KASAN_SHADOW_SCALE_SHIFT);
>> +
>> + return KASAN_SHADOW_OFFSET + scaled;
>> +}
>> +#endif
>
>Any reason this is moved up here?
I think it was necessary for something I added, removed and then didn't notice
it's no longer needed. I'll move it back.
--
Kind regards
Maciej Wieczór-Retman
