RE: [PATCH v2] mm: vmalloc: WARN_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 15:04
> To: Huang, Ying <ying.huang@linux.alibaba.com>
> Cc: Yadong Qi <yadong.qi@linux.alibaba.com>; urezki@gmail.com;
> linux-mm@kvack.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v2] mm: vmalloc: WARN_ON if mapping size is not PAGE_SIZE
> aligned
> 
> On Thu, 09 Oct 2025 14:38:27 +0800 "Huang, Ying"
> <ying.huang@linux.alibaba.com> wrote:
> 
> > Yadong Qi <yadong.qi@linux.alibaba.com> writes:
> >
> > > 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>
> > > ---
> > > v1 -> v2:
> > >   * Use WARN_ON instead of BUG_ON
> > > ---
> > >  mm/vmalloc.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 5edd536ba9d2..2cad593e4677 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)))
> > > +		return -ENOMEM;
> > > +
> >
> > EINVAL?
> >
> 
> If this errno gets returned to userspace somehow, programmer is going
> to wonder what was invalid about the arguments which the program passed
> to the kernel.
> 
> But either way, the callers of vmap_pte_range() should be audited, to
> verify that they take appropriate action when this happens.

I believe we should modify vmap_pmd_range(), vmap_pud_range(), and
vmap_p4d_range()
to accept an error code from the callee instead of simply returning -ENOMEM.
If there are no other suggestions, I will create a new patch.