linux-kernel - Re: [PATCH] mm/compaction: fix UBSAN shift-out-of-bounds warning

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Message-ID: <604bbcbb-e728-4aef-b95b-13d50f8c4cc8@redhat.com>
Date: Thu, 23 Jan 2025 10:19:27 +0100
From: David Hildenbrand <david@...hat.com>
To: Liu Shixin <liushixin2@...wei.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Kefeng Wang <wangkefeng.wang@...wei.com>,
 Kemeng Shi <shikemeng@...weicloud.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 Matthew Wilcox <willy@...radead.org>, Nanyong Sun <sunnanyong@...wei.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/compaction: fix UBSAN shift-out-of-bounds warning

On 23.01.25 03:10, Liu Shixin wrote:
> syzkaller reported a UBSAN shift-out-of-bounds warning of (1UL << order)
> in isolate_freepages_block(). The bogus compound_order can be any value
> because it is union with flags. Add back the MAX_PAGE_ORDER check to fix
> the warning.
> 
> Fixes: 3da0272a4c7d ("mm/compaction: correctly return failure with bogus compound_order in strict mode")
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> ---
>   mm/compaction.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a2b16b08cbbff..384e4672998e5 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -630,7 +630,8 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   		if (PageCompound(page)) {
>   			const unsigned int order = compound_order(page);
>   
> -			if (blockpfn + (1UL << order) <= end_pfn) {
> +			if ((order <= MAX_PAGE_ORDER) &&

hugetlb can exceed MAX_PAGE_ORDER, but end_pfn cannot. So I think what 
you have here will not change the exiting handling.

Acked-by: David Hildenbrand <david@...hat.com>


Note: the whole "-1" with stride != 1 looks odd ...

-- 
Cheers,

David / dhildenb