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

[Kees Cook]

On April 24, 2025 2:15:27 PM PDT, Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> 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