linux-kernel - Re: [PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

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Message-ID: <ZrXiBfS-Mv53gFO9@tiehlicka>
Date: Fri, 9 Aug 2024 11:31:49 +0200
From: Michal Hocko <mhocko@...e.com>
To: Hailong Liu <hailong.liu@...o.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Tangquan . Zheng" <zhengtangquan@...o.com>, stable@...r.kernel.org,
	Barry Song <21cnbao@...il.com>, Baoquan He <bhe@...hat.com>,
	Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages()
 with high order fallback to order 0

On Fri 09-08-24 11:30:32, Michal Hocko wrote:
> On Thu 08-08-24 20:00:58, Hailong Liu wrote:
> > The __vmap_pages_range_noflush() assumes its argument pages** contains
> > pages with the same page shift. However, since commit e9c3cda4d86e
> > (mm, vmalloc: fix high order __GFP_NOFAIL allocations), if gfp_flags
> > includes __GFP_NOFAIL with high order in vm_area_alloc_pages()
> > and page allocation failed for high order, the pages** may contain
> > two different page shifts (high order and order-0). This could
> > lead __vmap_pages_range_noflush() to perform incorrect mappings,
> > potentially resulting in memory corruption.
> > 
> > Users might encounter this as follows (vmap_allow_huge = true, 2M is for PMD_SIZE):
> > kvmalloc(2M, __GFP_NOFAIL|GFP_X)
> >     __vmalloc_node_range_noprof(vm_flags=VM_ALLOW_HUGE_VMAP)
> >         vm_area_alloc_pages(order=9) ---> order-9 allocation failed and fallback to order-0
> >             vmap_pages_range()
> >                 vmap_pages_range_noflush()
> >                     __vmap_pages_range_noflush(page_shift = 21) ----> wrong mapping happens
> > 
> > We can remove the fallback code because if a high-order
> > allocation fails, __vmalloc_node_range_noprof() will retry with
> > order-0. Therefore, it is unnecessary to fallback to order-0
> > here. Therefore, fix this by removing the fallback code.
> > 
> > Fixes: e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations")
> > Signed-off-by: Hailong Liu <hailong.liu@...o.com>
> > Reported-by: Tangquan.Zheng <zhengtangquan@...o.com>
> > Cc: <stable@...r.kernel.org>
> > CC: Barry Song <21cnbao@...il.com>
> > CC: Baoquan He <bhe@...hat.com>
> > CC: Matthew Wilcox <willy@...radead.org>
> > ---
> >  mm/vmalloc.c     | 11 ++---------
> >  mm/vmalloc.c.rej | 10 ++++++++++
> 
> What is this?
> 
> >  2 files changed, 12 insertions(+), 9 deletions(-)
> >  create mode 100644 mm/vmalloc.c.rej
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 6b783baf12a1..af2de36549d6 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3584,15 +3584,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >  			page = alloc_pages_noprof(alloc_gfp, order);
> >  		else
> >  			page = alloc_pages_node_noprof(nid, alloc_gfp, order);
> > -		if (unlikely(!page)) {
> > -			if (!nofail)
> > -				break;
> > -
> > -			/* fall back to the zero order allocations */
> > -			alloc_gfp |= __GFP_NOFAIL;
> > -			order = 0;
> > -			continue;
> > -		}
> > +		if (unlikely(!page))
> > +			break;
> 
> This just makes the NOFAIL allocation fail. So this is not a correct
> fix.

OK, I can see a newer version
-- 
Michal Hocko
SUSE Labs