linux-kernel - Re: [PATCH v5 04/19] x86: Add arch specific kasan functions

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Message-ID: <jcdmkdwfh4fmez6i4guyefiqhoz5kz6g6dvhdpiw3nxyeocjmk@juw3nevsqeds>
Date: Mon, 8 Sep 2025 11:06:47 +0200
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Andrey Konovalov <andreyknvl@...il.com>
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Subject: Re: [PATCH v5 04/19] x86: Add arch specific kasan functions

On 2025-09-06 at 19:17:43 +0200, Andrey Konovalov wrote:
>On Mon, Aug 25, 2025 at 10:27 PM Maciej Wieczor-Retman
><maciej.wieczor-retman@...el.com> wrote:
>>
>> KASAN's software tag-based mode needs multiple macros/functions to
>> handle tag and pointer interactions - to set, retrieve and reset tags
>> from the top bits of a pointer.
>>
>> Mimic functions currently used by arm64 but change the tag's position to
>> bits [60:57] in the pointer.
>>
>> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
>> ---
>> Changelog v4:
>> - Rewrite __tag_set() without pointless casts and make it more readable.
>>
>> Changelog v3:
>> - Reorder functions so that __tag_*() etc are above the
>>   arch_kasan_*() ones.
>> - Remove CONFIG_KASAN condition from __tag_set()
>>
>>  arch/x86/include/asm/kasan.h | 36 ++++++++++++++++++++++++++++++++++--
>>  1 file changed, 34 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
>> index d7e33c7f096b..1963eb2fcff3 100644
>> --- a/arch/x86/include/asm/kasan.h
>> +++ b/arch/x86/include/asm/kasan.h
>> @@ -3,6 +3,8 @@
>>  #define _ASM_X86_KASAN_H
>>
>>  #include <linux/const.h>
>> +#include <linux/kasan-tags.h>
>> +#include <linux/types.h>
>>  #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>>  #define KASAN_SHADOW_SCALE_SHIFT 3
>>
>> @@ -24,8 +26,37 @@
>>                                                   KASAN_SHADOW_SCALE_SHIFT)))
>>
>>  #ifndef __ASSEMBLER__
>> +#include <linux/bitops.h>
>> +#include <linux/bitfield.h>
>> +#include <linux/bits.h>
>> +
>> +#ifdef CONFIG_KASAN_SW_TAGS
>> +
>
>Nit: can remove this empty line.

Sure, will do, thanks.

>
>> +#define __tag_shifted(tag)             FIELD_PREP(GENMASK_ULL(60, 57), tag)
>> +#define __tag_reset(addr)              (sign_extend64((u64)(addr), 56))
>> +#define __tag_get(addr)                        ((u8)FIELD_GET(GENMASK_ULL(60, 57), (u64)addr))
>> +#else
>> +#define __tag_shifted(tag)             0UL
>> +#define __tag_reset(addr)              (addr)
>> +#define __tag_get(addr)                        0
>> +#endif /* CONFIG_KASAN_SW_TAGS */
>> +
>> +static inline void *__tag_set(const void *__addr, u8 tag)
>> +{
>> +       u64 addr = (u64)__addr;
>> +
>> +       addr &= ~__tag_shifted(KASAN_TAG_MASK);
>> +       addr |= __tag_shifted(tag);
>> +
>> +       return (void *)addr;
>> +}
>> +
>> +#define arch_kasan_set_tag(addr, tag)  __tag_set(addr, tag)
>> +#define arch_kasan_reset_tag(addr)     __tag_reset(addr)
>> +#define arch_kasan_get_tag(addr)       __tag_get(addr)
>>
>>  #ifdef CONFIG_KASAN
>> +
>>  void __init kasan_early_init(void);
>>  void __init kasan_init(void);
>>  void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid);
>> @@ -34,8 +65,9 @@ static inline void kasan_early_init(void) { }
>>  static inline void kasan_init(void) { }
>>  static inline void kasan_populate_shadow_for_vaddr(void *va, size_t size,
>>                                                    int nid) { }
>> -#endif
>>
>> -#endif
>> +#endif /* CONFIG_KASAN */
>> +
>> +#endif /* __ASSEMBLER__ */
>>
>>  #endif
>> --
>> 2.50.1
>>
>
>Acked-by: Andrey Konovalov <andreyknvl@...il.com>

-- 
Kind regards
Maciej Wieczór-Retman