linux-kernel - Re: [PATCH 2/4] mm: perform VMA allocation, freeing, duplication in mm

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Message-ID: <51903B43-2BFC-4BA6-9D74-63F79CF890B7@kernel.org>
Date: Thu, 24 Apr 2025 20:15:26 -0700
From: Kees Cook <kees@...nel.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
CC: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, David Hildenbrand <david@...hat.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm: perform VMA allocation, freeing, duplication in mm

On April 24, 2025 2:15:27 PM PDT, Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>+static void vm_area_init_from(const struct vm_area_struct *src,
>+			      struct vm_area_struct *dest)
>+{
>+	dest->vm_mm = src->vm_mm;
>+	dest->vm_ops = src->vm_ops;
>+	dest->vm_start = src->vm_start;
>+	dest->vm_end = src->vm_end;
>+	dest->anon_vma = src->anon_vma;
>+	dest->vm_pgoff = src->vm_pgoff;
>+	dest->vm_file = src->vm_file;
>+	dest->vm_private_data = src->vm_private_data;
>+	vm_flags_init(dest, src->vm_flags);
>+	memcpy(&dest->vm_page_prot, &src->vm_page_prot,
>+	       sizeof(dest->vm_page_prot));
>+	/*
>+	 * src->shared.rb may be modified concurrently when called from
>+	 * dup_mmap(), but the clone will reinitialize it.
>+	 */
>+	data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
>+	memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
>+	       sizeof(dest->vm_userfaultfd_ctx));
>+#ifdef CONFIG_ANON_VMA_NAME
>+	dest->anon_name = src->anon_name;
>+#endif
>+#ifdef CONFIG_SWAP
>+	memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
>+	       sizeof(dest->swap_readahead_info));
>+#endif
>+#ifdef CONFIG_NUMA
>+	dest->vm_policy = src->vm_policy;
>+#endif
>+}

I know you're doing a big cut/paste here, but why in the world is this function written this way? Why not just:

*dest = *src;

And then do any one-off cleanups?

-- 
Kees Cook