Re: [PATCH v6 08/39] mm: add mmap action for discontiguous kernel page mapping

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: mmap_action_finish bypasses error_override for compat tasks
--

commit 21d3d0c977ac349611c733fc3c288ae67e5f71a1
Author: Lorenzo Stoakes (ARM) <ljs@kernel.org>

mm: add mmap action for discontiguous kernel page mapping

This commit introduces discontig_kernel_page_ops and a new mmap action type
to allow drivers to map discontiguous arrays of kernel pages into a VMA.
It updates the compatibility layer via compat_mmap_action_abort() to properly
handle VMA teardown on mmap action failures.

> diff --git a/mm/util.c b/mm/util.c
> --- a/mm/util.c
> +++ b/mm/util.c

[ ... ]

> @@ -1412,12 +1421,13 @@ static int mmap_action_finish(struct vm_area_struct *vma,
>  
>  	/* do_munmap() might take rmap lock, so release if held. */
>  	maybe_rmap_unlock_action(vma, action);
> -	/*
> -	 * If this is invoked from the compatibility layer, post-mmap() hook
> -	 * logic will handle cleanup for us.
> -	 */
> -	if (!err || is_compat)
> +	if (!err)
> +		return 0;
> +
> +	if (is_compat) {
> +		compat_mmap_action_abort(vma);
>  		return err;

[Severity: Medium]
Does this bypass the error_override logic for compat tasks?

When an mmap action fails, the mmap_action struct provides an error_override
field to allow drivers to replace the internal error code with a user-facing
one. Later in this function, non-compat tasks return 
action->error_override ?: err.

By returning err directly here when is_compat is true, it seems 32-bit compat
tasks might receive different error codes than 64-bit tasks, potentially
breaking ABI consistency.

> +	}
>  
>  	/*
>  	 * If an error occurs, unmap the VMA altogether and return an error. We

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261013-b4-mmap-prepare-vma-flag-sanify-v6-0-1aa3c9b139f9@kernel.org?part=8