linux-kernel - Re: [PATCH v1 1/4] mm: Fix uprobe pte be overwritten when expanding vma

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Message-ID: <6dd3af08-b3be-4a68-af3d-1fc1b79f4279@redhat.com>
Date: Mon, 2 Jun 2025 14:26:21 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Pu Lehui <pulehui@...weicloud.com>, mhiramat@...nel.org, oleg@...hat.com,
 peterz@...radead.org, akpm@...ux-foundation.org, Liam.Howlett@...cle.com,
 vbabka@...e.cz, jannh@...gle.com, pfalcato@...e.de, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, pulehui@...wei.com
Subject: Re: [PATCH v1 1/4] mm: Fix uprobe pte be overwritten when expanding
 vma

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()


But maybe I'm getting lost in the code. (e.g., expand_vma() vs. 
vma_expand() ... confusing :) )

-- 
Cheers,

David / dhildenb