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

[SJ Park <sj@kernel.org>]

On Sun, 05 Jul 2026 16:06:50 +0000 sashiko-bot@kernel.org wrote:

> 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()`.

No blocker.  Read below for details, please.

> --
> 
> 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.

Yes, that's how it works, and I find no problem here.  No bad consequences like
kernel panic happenns.  It it might be confusing and better to improve for user
experience.  However, I don't think this corner case experience deserves the
additional complexity.  I want to keep the validation simple and minimum.

So I will keep this as is unless others chime in.

> 
> >  	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

Thankss,
SJ