Re: [PATCH v10 09/22] kasan: add tag related helper functions

[Andrey Konovalov]

On Wed, Nov 7, 2018 at 6:23 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Tue, Nov 06, 2018 at 06:30:24PM +0100, Andrey Konovalov wrote:
>> This commit adds a few helper functions, that are meant to be used to
>> work with tags embedded in the top byte of kernel pointers: to set, to
>> get or to reset (set to 0xff) the top byte.
>>
>> Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
>> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>> ---
>>  arch/arm64/mm/kasan_init.c |  2 ++
>>  include/linux/kasan.h      | 13 +++++++++
>>  mm/kasan/kasan.h           | 55 ++++++++++++++++++++++++++++++++++++++
>>  mm/kasan/tags.c            | 37 +++++++++++++++++++++++++
>>  4 files changed, 107 insertions(+)
>>
>> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
>> index 18ebc8994a7b..370b19d0e2fb 100644
>> --- a/arch/arm64/mm/kasan_init.c
>> +++ b/arch/arm64/mm/kasan_init.c
>> @@ -249,6 +249,8 @@ void __init kasan_init(void)
>>       memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
>>       cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
>>
>> +     kasan_init_tags();
>> +
>>       /* At this point kasan is fully initialized. Enable error messages */
>>       init_task.kasan_depth = 0;
>>       pr_info("KernelAddressSanitizer initialized\n");
>> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
>> index 7f6574c35c62..4c9d6f9029f2 100644
>> --- a/include/linux/kasan.h
>> +++ b/include/linux/kasan.h
>> @@ -169,6 +169,19 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
>>
>>  #define KASAN_SHADOW_INIT 0xFF
>>
>> +void kasan_init_tags(void);
>> +
>> +void *kasan_reset_tag(const void *addr);
>> +
>> +#else /* CONFIG_KASAN_SW_TAGS */
>> +
>> +static inline void kasan_init_tags(void) { }
>> +
>> +static inline void *kasan_reset_tag(const void *addr)
>> +{
>> +     return (void *)addr;
>> +}
>> +
>
>> +#ifdef CONFIG_KASAN_SW_TAGS
>> +
>> +#define KASAN_PTR_TAG_SHIFT 56
>> +#define KASAN_PTR_TAG_MASK (0xFFUL << KASAN_PTR_TAG_SHIFT)
>> +
>> +u8 random_tag(void);
>> +
>> +static inline void *set_tag(const void *addr, u8 tag)
>> +{
>> +     u64 a = (u64)addr;
>> +
>> +     a &= ~KASAN_PTR_TAG_MASK;
>> +     a |= ((u64)tag << KASAN_PTR_TAG_SHIFT);
>> +
>> +     return (void *)a;
>> +}
>> +
>> +static inline u8 get_tag(const void *addr)
>> +{
>> +     return (u8)((u64)addr >> KASAN_PTR_TAG_SHIFT);
>> +}
>> +
>> +static inline void *reset_tag(const void *addr)
>> +{
>> +     return set_tag(addr, KASAN_TAG_KERNEL);
>> +}
>
> We seem to be duplicating this functionality in several places.
>
> Could we please make it so that the arch code defines macros:
>
> arch_kasan_set_tag(addr, tag)
> arch_kasan_get_tag(addr)
> arch_kasan_reset_tag(addr)
>
> ... and use thoses consistently rather than open-coding them?
>
>> +
>> +#else /* CONFIG_KASAN_SW_TAGS */
>> +
>> +static inline u8 random_tag(void)
>> +{
>> +     return 0;
>> +}
>> +
>> +static inline void *set_tag(const void *addr, u8 tag)
>> +{
>> +     return (void *)addr;
>> +}
>> +
>> +static inline u8 get_tag(const void *addr)
>> +{
>> +     return 0;
>> +}
>> +
>> +static inline void *reset_tag(const void *addr)
>> +{
>> +     return (void *)addr;
>> +}
>
> ... these can be defined in linux/kasan.h as:
>
> #define arch_kasan_set_tag(addr, tag)   (addr)
> #define arch_kasan_get_tag(addr)        0
> #define arch_kasan_reset_tag(addr)      (addr)

Will do in v11, thanks!