linux-kernel - Re: [RFC PATCH] mm/mmap: Fix uprobe anon page be overwritten when expanding vma during mremap

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Message-ID: <e93e30db-8c78-4bb6-825f-a538825c6375@huaweicloud.com>
Date: Tue, 27 May 2025 21:23:45 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: David Hildenbrand <david@...hat.com>, lorenzo.stoakes@...cle.com,
 mhiramat@...nel.org, peterz@...radead.org, Liam.Howlett@...cle.com,
 akpm@...ux-foundation.org, vbabka@...e.cz, jannh@...gle.com,
 pfalcato@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 pulehui@...wei.com
Subject: Re: [RFC PATCH] mm/mmap: Fix uprobe anon page be overwritten when
 expanding vma during mremap



On 2025/5/26 23:48, Oleg Nesterov wrote:
> Hi Lehui,
> 
> As I said, I don't understand mm/, so can't comment, but...
> 
> On 05/26, Pu Lehui wrote:
>>
>> To make things simpler, perhaps we could try post-processing, that is:
>>
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 83e359754961..46a757fd26dc 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -240,6 +240,11 @@ static int move_ptes(struct pagetable_move_control
>> *pmc,
>>                  if (pte_none(ptep_get(old_pte)))
>>                          continue;
>>
>> +               /* skip move pte when expanded range has uprobe */
>> +               if (unlikely(pte_present(*new_pte) &&
>> +                            vma_has_uprobes(pmc->new, new_addr, new_addr +
>> PAGE_SIZE)))
>> +                       continue;
>> +
> 
> I was thinking about
> 
> 	WARN_ON(!pte_none(*new_pte))
> 
> at the start of the main loop.
> 
> Obviously not to fix the problem, but rather to make it more explicit.
> 
> This matches the similar xxx_none() checks in the move_pgt_entry() paths,
> say, move_normal_pmd().
> 
> Oleg.

Got it. It will help identify problems in time.