[PATCH v12 06/15] kasan: arm64: x86: Make page_to_virt() KASAN aware

[Will Deacon]

On Mon, Mar 30, 2026 at 02:33:43PM +0000, Maciej Wieczor-Retman wrote:
> From: Maciej Wieczor-Retman <maciej.wieczor-retman at intel.com>
> 
> Special page_to_virt() implementation is needed if an architecture wants
> to enable KASAN software tag-based mode.
> 
> Make page_to_virt() KASAN aware in arch-independent code so
> architectures implementing the software tag-based mode don't have to
> define their own implementations anymore. When KASAN is disabled or for
> architectures that don't implement the software tag-based mode
> page_to_virt() will be optimized to it's previous form.
> 
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman at intel.com>
> ---
> Changelog v11:
> - Redo the patch to work on the page_to_virt macro. Split off changes
>   about virt to phys conversion to an earlier patch.
> - Remove Alexander's acked-by due to bigger changes.
> 
> Changelog v7:
> - Add Alexander's Acked-by tag.
> 
> Changelog v5:
> - Move __tag_reset() calls into __phys_addr_nodebug() and
>   __virt_addr_valid() instead of calling it on the arguments of higher
>   level functions.
> 
> Changelog v4:
> - Simplify page_to_virt() by removing pointless casts.
> - Remove change in __is_canonical_address() because it's taken care of
>   in a later patch due to a LAM compatible definition of canonical.
> 
>  arch/arm64/include/asm/memory.h |  5 -----
>  include/linux/kasan.h           | 10 ++++++++++
>  include/linux/mm.h              |  5 ++++-
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 875c0bd0d85a..39dd0071d3ec 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -411,11 +411,6 @@ static inline unsigned long virt_to_pfn(const void *kaddr)
>   */
>  
>  #if defined(CONFIG_DEBUG_VIRTUAL)
> -#define page_to_virt(x)	({						\
> -	__typeof__(x) __page = x;					\
> -	void *__addr = __va(page_to_phys(__page));			\
> -	(void *)__tag_set((const void *)__addr, page_kasan_tag(__page));\
> -})

So here we're using '__page' to avoid multiple evaluations of 'x'...

>  #define virt_to_page(x)		pfn_to_page(virt_to_pfn(x))
>  #else
>  #define page_to_virt(x)	({						\
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index e18908f3ad6e..271c59e9f422 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -527,6 +527,11 @@ static inline void *kasan_reset_tag(const void *addr)
>  	return (void *)arch_kasan_reset_tag(addr);
>  }
>  
> +static inline void *kasan_set_tag(const void *addr, u8 tag)
> +{
> +	return (void *)arch_kasan_set_tag(addr, tag);
> +}
> +
>  /**
>   * kasan_report - print a report about a bad memory access detected by KASAN
>   * @addr: address of the bad access
> @@ -544,6 +549,11 @@ static inline void *kasan_reset_tag(const void *addr)
>  	return (void *)addr;
>  }
>  
> +static inline void *kasan_set_tag(const void *addr, u8 tag)
> +{
> +	return (void *)addr;
> +}
> +
>  #endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS*/
>  
>  #ifdef CONFIG_KASAN_HW_TAGS
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 09044934dda8..f234650a4edf 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -117,7 +117,10 @@ extern int mmap_rnd_compat_bits __read_mostly;
>  #endif
>  
>  #ifndef page_to_virt
> -#define page_to_virt(x)	__va(PFN_PHYS(page_to_pfn(x)))
> +#define page_to_virt(x) ({							\
> +	void *__addr = __va(PFN_PHYS(page_to_pfn((struct page *)x)));		\
> +	kasan_set_tag(__addr, page_kasan_tag(x));				\
> +})

... but in the new code you're proposing, you evaluate 'x' twice.

Is there a reason not to take the arm64 code as-is?

Will