Re: [PATCH] mm: vmalloc: BUG_ON if mapping size is not PAGE_SIZE aligned

[Andrew Morton]

On Thu,  9 Oct 2025 11:59:43 +0800 Yadong Qi <yadong.qi@xxxxxxxxxxxxxxxxx> wrote:

> In mm/vmalloc.c, the function vmap_pte_range() assumes that the
> mapping size is aligned to PAGE_SIZE. If this assumption is
> violated, the loop will become infinite because the termination
> condition (`addr != end`) will never be met. This can lead to
> overwriting other VA ranges and/or random pages physically follow
> the page table.
> 
> It's the caller's responsibility to ensure that the mapping size
> is aligned to PAGE_SIZE. However, the memory corruption is hard
> to root cause. To identify the programming error in the caller
> easier, check whether the mapping size is PAGE_SIZE aligned with
> BUG_ON().
> 
> ..
>
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -100,6 +100,8 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>  	struct page *page;
>  	unsigned long size = PAGE_SIZE;
>  
> +	BUG_ON(!PAGE_ALIGNED(end - addr));
> +
>  	pfn = phys_addr >> PAGE_SHIFT;
>  	pte = pte_alloc_kernel_track(pmd, addr, mask);
>  	if (!pte)

We try to avoid adding BUG()s - deliberately crashing the kernel is
pretty cruel to the user.  It's far better to WARN and to continue in
some fashion so the user can at least gather logs, etc.

How about

	if (WARN_ON(!PAGE_ALIGNED(end - addr)))
		return -ENOMEM;

?

(Or VM_WARN_ON)