Re: [PATCH 7/8] mm/damon/core: remove start, end check in damon_set_region_system_rams()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Removing the explicit `*start > *end` check causes invalid, inverted memory ranges to be inconsistently accepted due to post-alignment bounds checking in `damon_set_regions()`.
--

commit f561b43e79bb90540b8053e4d95593cfb96f6d1d
Author: SJ Park <sj@kernel.org>

mm/damon/core: remove start, end check in damon_set_region_system_rams()

This commit removes the explicit start and end validation in
damon_set_region_system_rams_default(), relying instead on the bounds check
inside damon_set_regions() to catch invalid ranges.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -3846,9 +3846,6 @@ int damon_set_region_system_rams_default(struct damon_target *t,
>  {
>  	struct damon_addr_range addr_range;
>  
> -	if (*start > *end)
> -		return -EINVAL;
> -

[Severity: Medium]
Does removing this check allow inverted ranges to bypass validation?

Looking at damon_set_regions() in mm/damon/core.c, the fallback check
evaluates the values post-alignment:

mm/damon/core.c:damon_set_regions() {
	for (i = 0; i < nr_ranges; i++) {
		unsigned long start, end;

		start = ALIGN_DOWN(ranges[i].start, min_region_sz);
		end = ALIGN(ranges[i].end, min_region_sz);
		if (start >= end)
			return -EINVAL;
	...
}

If an administrator configures an unaligned, inverted memory range
(for example, start=8191, end=4097), the post-alignment check might still
evaluate to ALIGN_DOWN(start) < ALIGN(end) and accept the invalid inputs.

>  	if (!*start && !*end &&
>  		!damon_find_system_rams_range(start, end, addr_unit))
>  		return -EINVAL;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260705155600.96555-1-sj@kernel.org?part=7