[v5] kasan: x86: arm64: KASAN tag-based mode for x86

[PATCH v5 04/19] x86: Add arch specific kasan functions

Posted by Maciej Wieczor-Retman 5 months, 2 weeks ago

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@intel.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
+
+#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

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

Posted by Andrey Ryabinin 4 months, 3 weeks ago

On 8/25/25 10:24 PM, Maciej Wieczor-Retman wrote:

> +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;
> +}
> +


This requires some ifdef magic to avoid getting this into vdso32 image build process,
otherwise we'll get this warning:

CC      arch/x86/entry/vdso/vdso32/vclock_gettime.o
In file included from ../arch/x86/include/asm/page.h:10,
                 from ../arch/x86/include/asm/processor.h:20,
                 from ../arch/x86/include/asm/timex.h:5,
                 from ../include/linux/timex.h:67,
                 from ../include/linux/time32.h:13,
                 from ../include/linux/time.h:60,
                 from ../arch/x86/entry/vdso/vdso32/../vclock_gettime.c:11,
                 from ../arch/x86/entry/vdso/vdso32/vclock_gettime.c:4:
../arch/x86/include/asm/kasan.h: In function ‘__tag_set’:
../arch/x86/include/asm/kasan.h:81:20: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   81 |         u64 addr = (u64)__addr;
      |                    ^
../arch/x86/include/asm/kasan.h:86:16: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   86 |         return (void *)addr;
      |                ^

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

Posted by Maciej Wieczor-Retman 4 months, 3 weeks ago

On 2025-09-18 at 17:52:39 +0200, Andrey Ryabinin wrote:
>
>On 8/25/25 10:24 PM, Maciej Wieczor-Retman wrote:
>
>> +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;
>> +}
>> +
>
>
>This requires some ifdef magic to avoid getting this into vdso32 image build process,
>otherwise we'll get this warning:
>
>CC      arch/x86/entry/vdso/vdso32/vclock_gettime.o
>In file included from ../arch/x86/include/asm/page.h:10,
>                 from ../arch/x86/include/asm/processor.h:20,
>                 from ../arch/x86/include/asm/timex.h:5,
>                 from ../include/linux/timex.h:67,
>                 from ../include/linux/time32.h:13,
>                 from ../include/linux/time.h:60,
>                 from ../arch/x86/entry/vdso/vdso32/../vclock_gettime.c:11,
>                 from ../arch/x86/entry/vdso/vdso32/vclock_gettime.c:4:
>../arch/x86/include/asm/kasan.h: In function ‘__tag_set’:
>../arch/x86/include/asm/kasan.h:81:20: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
>   81 |         u64 addr = (u64)__addr;
>      |                    ^
>../arch/x86/include/asm/kasan.h:86:16: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>   86 |         return (void *)addr;
>      |                ^
>

Thanks for noticing that, I'll fix it :)

-- 
Kind regards
Maciej Wieczór-Retman

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

Posted by Andrey Konovalov 5 months ago

On Mon, Aug 25, 2025 at 10:27 PM Maciej Wieczor-Retman
<maciej.wieczor-retman@intel.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@intel.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.

> +#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@gmail.com>

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

Posted by Maciej Wieczor-Retman 5 months ago

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@intel.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@intel.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@gmail.com>

-- 
Kind regards
Maciej Wieczór-Retman