Re: [PATCH RFC 17/37] arm64: mte: Disable dynamic tag storage management if HW KASAN is enabled

[Hyesoo Yu]

On Wed, Aug 23, 2023 at 02:13:30PM +0100, Alexandru Elisei wrote:
> Reserving the tag storage associated with a tagged page requires the
> ability to migrate existing data if the tag storage is in use for data.
> 
> The kernel allocates pages, which are now tagged because of HW KASAN, in
> non-preemptible contexts, which can make reserving the associate tag
> storage impossible.
> 
> Don't expose the tag storage pages to the memory allocator if HW KASAN is
> enabled.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
>  arch/arm64/kernel/mte_tag_storage.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
> index 4a6bfdf88458..f45128d0244e 100644
> --- a/arch/arm64/kernel/mte_tag_storage.c
> +++ b/arch/arm64/kernel/mte_tag_storage.c
> @@ -314,6 +314,18 @@ static int __init mte_tag_storage_activate_regions(void)
>  		return 0;
>  	}
>  
> +	/*
> +	 * The kernel allocates memory in non-preemptible contexts, which makes
> +	 * migration impossible when reserving the associated tag storage.
> +	 *
> +	 * The check is safe to make because KASAN HW tags are enabled before
> +	 * the rest of the init functions are called, in smp_prepare_boot_cpu().
> +	 */
> +	if (kasan_hw_tags_enabled()) {
> +		pr_info("KASAN HW tags enabled, disabling tag storage");
> +		return 0;
> +	}
> +

Hi.

Is there no plan to enable HW KASAN in the current design ? 
I wonder if dynamic MTE is only used for user ? 

Thanks,
Hyesoo Yu.


>  	for (i = 0; i < num_tag_regions; i++) {
>  		tag_range = &tag_regions[i].tag_range;
>  		for (pfn = tag_range->start; pfn <= tag_range->end; pfn += pageblock_nr_pages) {
> -- 
> 2.41.0
> 
>