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[2003:d8:2f03:5b00:f549:a879:b2d3:73ee]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4f009fdbasm4086329f8f.85.2025.05.30.01.33.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 30 May 2025 01:33:17 -0700 (PDT) Message-ID: Date: Fri, 30 May 2025 10:33:16 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm/mmap: Fix uprobe anon page be overwritten when expanding vma during mremap To: Pu Lehui , Oleg Nesterov Cc: lorenzo.stoakes@oracle.com, mhiramat@kernel.org, peterz@infradead.org, Liam.Howlett@oracle.com, akpm@linux-foundation.org, vbabka@suse.cz, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, pulehui@huawei.com References: <20250521092503.3116340-1-pulehui@huaweicloud.com> <62b5ccf5-f1cd-43c2-b0bc-f542f40c5bdf@redhat.com> <13c5fe73-9e11-4465-b401-fc96a22dc5d1@redhat.com> <4cbc1e43-ea46-44de-9e2b-1c62dcd2b6d5@huaweicloud.com> <20250526154850.GA4156@redhat.com> <06bd94c0-fefe-4bdc-8483-2d9b6703c3d6@redhat.com> <57533126-eb30-4b56-bc4d-2f27514ae5ad@huaweicloud.com> <956124be-c73c-4023-9edd-25372f3f865a@huaweicloud.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 29.05.25 18:07, Pu Lehui wrote: > > On 2025/5/28 17:03, David Hildenbrand wrote: >> On 27.05.25 15:38, Pu Lehui wrote: >>> Hi David, >>> >>> On 2025/5/27 2:46, David Hildenbrand wrote: >>>> On 26.05.25 17:48, 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. >>>> >>>> Yeah, WARN_ON_ONCE(). >>>> >>>> We really should fix the code to not install uprobes into the area we >>>> are moving. >>> Alright, so let's try this direction. >>> >>>> >>>> Likely, the correct fix will be to pass the range as well to >>>> uprobe_mmap(), and passing that range to build_probe_list(). >>> >>> It will be great. But IIUC, the range we expand to is already included >>> when entering uprobe_mmap and also build_probe_list. >> >> Right, you'd have to communicate that information through all layers >> (expanded range). >> >> As an alternative, maybe we can really call handle_vma_uprobe() after >> moving the pages. > > Hi David, > > Not sure if this is possible, but I think it would be appropriate to not > handle this uprobe_mmap at the source, and maybe we should make it clear > that new_pte must be NULL when move_ptes, otherwise it should be an > exception? Yeah, we should ay least document that if we find any non-none pte in the range we are moving to, we have a big problem. I think the main issue is that vma_complete() calls uprobe_mmap() before moving the page tables over. If we could defer the uprobe_mmap() call, we might be good. The entry point is copy_vma_and_data(), where we call copy_vma() before move_page_tables(). copy_vma() should trigger the uprobe_mmap() through vma_merge_new_range(). I wonder if there might be a clean way to move the uprobe_mmap() out of vma_complete(). (or at least specify to skip it because it will be done manually). -- Cheers, David / dhildenb