RE: [PATCH v3] mm: vmalloc: WARN_ON if mapping size is not PAGE_SIZE aligned

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

> -----Original Message-----
> From: Uladzislau Rezki <urezki@gmail.com>
> Sent: 2025年10月9日 17:46
> To: Yadong Qi <yadong.qi@linux.alibaba.com>
> Cc: akpm@linux-foundation.org; urezki@gmail.com; linux-mm@kvack.org;
> linux-kernel@vger.kernel.org; ying.huang@linux.alibaba.com
> Subject: Re: [PATCH v3] mm: vmalloc: WARN_ON if mapping size is not PAGE_SIZE
> aligned
> 
> On Thu, Oct 09, 2025 at 05:37:06PM +0800, Yadong Qi 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
> > WARN_ON().
> >
> > Signed-off-by: Yadong Qi <yadong.qi@linux.alibaba.com>
> > Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
> > ---
> > v2 -> v3:
> >   * change error code from ENOMEM to EINVAL
> >   * modify callers of vmap_pte_range to handle return code
> > v1 -> v2:
> >   * Use WARN_ON instead of BUG_ON
> > ---
> >  mm/vmalloc.c | 29 ++++++++++++++++++-----------
> >  1 file changed, 18 insertions(+), 11 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 5edd536ba9d2..1fa52f203795 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -100,6 +100,9 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long
> addr, unsigned long end,
> >  	struct page *page;
> >  	unsigned long size = PAGE_SIZE;
> >
> > +	if (WARN_ON(!PAGE_ALIGNED(end - addr)))
> >
> And it might be worth to use WARN_ON_ONCE() otherwise there is a risk
> that a kernel buffer would contain only such warnings.
> 

Sure, will change in next version.

Best Regard
Yadong