[PATCH mm-hotfixes v3 1/4] mm/vmalloc: acquire init_mm lock on huge vmap to avoid ptdump UAF

[David Hildenbrand (Arm)]

>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/vmalloc.h>
> @@ -158,10 +159,25 @@ static int vmap_try_huge_pmd(pmd_t *pmd, unsigned long addr, unsigned long end,
>  	if (!IS_ALIGNED(phys_addr, PMD_SIZE))
>  		return 0;
>  
> -	if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr))
> -		return 0;
> +	if (!pmd_present(*pmd))
> +		return pmd_set_huge(pmd, phys_addr, prot);
>  
> -	return pmd_set_huge(pmd, phys_addr, prot);
> +	/*
> +	 * Kernel page table walkers either walk ranges they own exclusively or
> +	 * hold the mmap write lock on init_mm (ptdump being the motivating
> +	 * case).
> +	 *
> +	 * Therefore, acquire the mmap read lock to prevent use-after-free when
> +	 * freeing page tables.
> +	 */

Can you spell out here why arm64 is special?

-- 
Cheers,

David