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

[<yadong.qi@linux.alibaba.com>]

> -----Original Message-----
> From: Andrew Morton <akpm@linux-foundation.org>
> Sent: 2025年10月9日 12:17
> To: Yadong Qi <yadong.qi@linux.alibaba.com>
> Cc: urezki@gmail.com; linux-mm@kvack.org; linux-kernel@vger.kernel.org;
> ying.huang@linux.alibaba.com
> Subject: Re: [PATCH] mm: vmalloc: BUG_ON if mapping size is not PAGE_SIZE
> aligned
> 
> On Thu,  9 Oct 2025 11:59:43 +0800 Yadong Qi <yadong.qi@linux.alibaba.com>
> 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)

Sure, I will send a new patch with WARN_ON.

Best Regard
Yadong