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[2003:d8:2f0d:f000:eec9:2b8d:4913:f32a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7f8edebsm158198345e9.6.2025.06.03.05.16.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jun 2025 05:16:38 -0700 (PDT) Message-ID: <6d7c2cd2-061e-4295-8e9a-832cd0185d8c@redhat.com> Date: Tue, 3 Jun 2025 14:16:37 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/4] mm: Fix uprobe pte be overwritten when expanding vma To: Lorenzo Stoakes Cc: Pu Lehui , mhiramat@kernel.org, oleg@redhat.com, peterz@infradead.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, pulehui@huawei.com References: <20250529155650.4017699-1-pulehui@huaweicloud.com> <20250529155650.4017699-2-pulehui@huaweicloud.com> <962c6be7-e37a-4990-8952-bf8b17f6467d@redhat.com> <009fe1d5-9d98-45f1-89f0-04e2ee8f0ade@lucifer.local> <6dd3af08-b3be-4a68-af3d-1fc1b79f4279@redhat.com> <117e92c1-d514-4661-a04b-abe663a72995@lucifer.local> <702d4035-281f-4045-aaa7-3d6c3f7bdb68@redhat.com> <86b7cfb9-65d2-4737-a84d-e151702895f1@lucifer.local> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 02.06.25 19:01, Lorenzo Stoakes wrote: > On Mon, Jun 02, 2025 at 06:28:58PM +0200, David Hildenbrand wrote: >> On 02.06.25 15:26, Lorenzo Stoakes wrote: >>> On Mon, Jun 02, 2025 at 02:26:21PM +0200, David Hildenbrand wrote: >>>> On 02.06.25 13:55, Lorenzo Stoakes wrote: >>>>> On Fri, May 30, 2025 at 08:51:14PM +0200, David Hildenbrand wrote: >>>>>>> if (vp->remove) { >>>>>>> @@ -1823,6 +1829,14 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >>>>>>> faulted_in_anon_vma = false; >>>>>>> } >>>>>>> + /* >>>>>>> + * If the VMA we are copying might contain a uprobe PTE, ensure >>>>>>> + * that we do not establish one upon merge. Otherwise, when mremap() >>>>>>> + * moves page tables, it will orphan the newly created PTE. >>>>>>> + */ >>>>>>> + if (vma->vm_file) >>>>>>> + vmg.skip_vma_uprobe = true; >>>>>>> + >>>>>> >>>>>> Assuming we extend the VMA on the way (not merge), would we handle that >>>>>> properly? >>>>>> >>>>>> Or is that not possible on this code path or already broken either way? >>>>> >>>>> I'm not sure in what context you mean expand, vma_merge_new_range() calls >>>>> vma_expand() so we call an expand a merge here, and this flag will be >>>>> obeyed. >>>> >>>> Essentially, an mremap() that grows an existing mapping while moving it. >>>> >>>> Assume we have >>>> >>>> [ VMA 0 ] [ VMA X] >>>> >>>> And want to grow VMA 0 by 1 page. >>>> >>>> We cannot grow in-place, so we'll have to copy VMA 0 to another VMA, and >>>> while at it, expand it by 1 page. >>>> >>>> expand_vma()->move_vma()->copy_vma_and_data()->copy_vma() >>> >>> OK so in that case you'd not have a merge at all, you'd have a new VMA and all >>> would be well and beautiful :) or I mean hopefully. Maybe? >> >> I'm really not sure. :) >> >> Could there be some very odd cases like >> >> [VMA 0 ][ VMA 1 ][ VMA X] >> >> and when we mremap() [ VMA 1 ] to grow, we would place it before [VMA 0 ], >> and just by pure lick end up merging with that if the ranges match? > > When we invoke copy_vma() we pass vrm->new_addr and vrm->new_len so this would > trigger a merge and the correct uprobe handling. > > Since we just don't trigger the breakpoint install in this situation, we'd > correctly move over the breakpoint to the right position, and overwrite anything > we expanded into. > > I do want to do a mremap doc actually to cover all the weird cases, because > there's some weird stuff in there and it's worth covering off stuff for users > and stuff for kernel people :) > >> >> We're in the corner cases now, ... so this might not be relevant. But I hope >> we can clean up that uprobe mmap call later ... > > Yeah with this initial fix in we can obviously revisit as needed! As Andrew was asking off-list: Acked-by: David Hildenbrand :) -- Cheers, David / dhildenb