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[2003:d8:2f34:a300:1c2c:f35e:e8e5:488e]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4efe5b79asm15145126f8f.2.2025.06.02.09.28.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Jun 2025 09:28:59 -0700 (PDT) Message-ID: <702d4035-281f-4045-aaa7-3d6c3f7bdb68@redhat.com> Date: Mon, 2 Jun 2025 18:28:58 +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> 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 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? 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 ... > >> >> >> But maybe I'm getting lost in the code. (e.g., expand_vma() vs. vma_expand() >> ... confusing :) ) > > Yeah I think Liam or somebody else called me out for this :P I mean it's > accurate naming in mremap.c but that's kinda in the context of the mremap. > > For VMA merging vma_expand() is used generally for a new VMA, since you're > always expanding into the gap, but because we all did terrible things in past > lives also called by relocate_vma_down() which is a kinda-hack for initial stack > relocation on initial process setup. > > It maybe needs renaming... But expand kinda accurately describes what's going on > just semi-overloaded vs. mremap() now :>) > > VMA merge code now at least readable enough that you can pick up on the various > oddnesses clearly :P :) -- Cheers, David / dhildenb