Re: [PATCH v10 32/38] dyndbg: resolve "protection" of class'd pr_debug

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] dyndbg: module's own classmaps bypass protection due to missing controlling_param init
- [Medium] dyndbg: data race on map->controlling_param due to lockless initialization
--

commit 5ffc9f5551765ac7c4413f320b8e9d1977dbe99a
Author: Jim Cromie <jim.cromie@gmail.com>

dyndbg: resolve "protection" of class'd pr_debug

This commit updates the protection mechanism for class'd pr_debug callsites
against unclassed queries. It introduces a requirement that a sysfs parameter
(controlling_param) must be present for a classmap to be protected.

> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index c023d07623f29..ac54a0499369c 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c

[ ... ]

> @@ -257,7 +300,28 @@ static bool ddebug_match_desc(const struct ddebug_query *query,
>  	    dp->lineno > query->last_lineno)
>  		return false;
>  
> -	return true;
> +	/*
> +	 * above are all satisfied, so we can make final decisions:
> +	 * 1- class FOO or implied class __DEFAULT__
> +	 * 2- site.is_classed or not
> +	 */
> +	if (query->class_string) {
> +		/* class FOO given, exact match required */
> +		return (dp->class_id == selected_class);
> +	}
> +	/* query class __DEFAULT__ by omission. */
> +	if (dp->class_id == _DPRINTK_CLASS_DFLT) {
> +		/* un-classed site */
> +		return true;
> +	}
> +	/* site is class'd */
> +	site_map = ddebug_find_map_by_class_id(di, dp->class_id);
> +	if (!site_map) {
> +		WARN_ONCE(1, "unknown class_id %d, check %s's CLASSMAP definitions", dp->class_id, di->mod_name);
> +		return false;
> +	}
> +	/* module(-param) decides protection */
> +	return !ddebug_class_wants_protection(site_map);

[Severity: High]
Does this code inadvertently bypass ABI protection for a module's own
class'd pr_debug sites?

Since the ddebug_apply_class_maps() block was removed in v10, it appears
ddebug_add_module() only initializes user maps (by calling
ddebug_apply_class_users() when dt->info.users.len > 0), and misses
initializing the defining module's own native classmaps.

Consequently, if a module defines a classmap and parameter but has no
loaded dependent modules, map->controlling_param remains NULL. This causes
ddebug_class_wants_protection() to default to false, allowing unclassed
legacy queries to incorrectly modify these protected sites.

>  }
>  

[ ... ]

> +static void ddebug_match_apply_kparam(const struct kernel_param *kp,
> +				      struct ddebug_class_map *map,
> +				      const char *mod_name)
> +{
> +	struct ddebug_class_param *dcp = ddebug_get_classmap_kparam(kp, map);
>  
>  	if (dcp && dcp->map == map) {
> +		map->controlling_param = dcp;

[Severity: Medium]
Can this assignment introduce a data race?

In ddebug_add_module(), the new debug table is published to the globally
visible ddebug_tables list under ddebug_lock, but the lock is released
before calling ddebug_apply_class_users().

Since ddebug_match_apply_kparam() is subsequently called without locks,
concurrent threads processing ddebug_change() could hold ddebug_lock
and read map->controlling_param while it is being updated here, leading
to a data race.

>  		v2pr_info(" kp:%s.%s =0x%x", mod_name, kp->name, *dcp->bits);
>  		vpr_cm_info(map, " %s maps ", mod_name);
>  		ddebug_sync_classbits(kp, mod_name);
>  	}
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260916-dd-cmap-part2-clean-v10-0-af4cf4767707@gmail.com?part=32