Re: [PATCH v7 24/29] dyndbg: pin class param storage to u32

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Bitwise shift out-of-bounds on 32-bit architectures when evaluating `BIT(bi)` in `ddebug_apply_class_bitmap()`.
--

--- Patch [24]: [PATCH v7 24/29] dyndbg: pin class param storage to u32 ---
commit 87a65c25e24b4e05bdc18ddf16105e9237d922db
Author: Jim Cromie <jim.cromie@gmail.com>

dyndbg: pin class param storage to u32

This commit changes the bits and lvl fields in struct ddebug_class_param
to use u32 instead of unsigned long. This ensures consistent sizing across
different architectures.

> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index 59e3c0eccbede..60b67face46e1 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c

[ ... ]

> @@ -643,24 +643,27 @@ static int ddebug_apply_class_bitmap(const struct ddebug_class_param *dcp,
>  	int bi, ct;
>  
>  	if (*new_bits != old_bits)
> -		v2pr_info("apply bitmap: 0x%lx to: 0x%lx for %s\n", *new_bits,
> +		v2pr_info("apply bitmap: 0x%x to: 0x%x for %s\n", *new_bits,
>  			  old_bits, query_modname ?: "'*'");
>  
>  	for (bi = 0; bi < map->length; bi++) {
> -		if (test_bit(bi, new_bits) == test_bit(bi, &old_bits))
> +		bool new_b = !!(*new_bits & BIT(bi));
> +		bool old_b = !!(old_bits & BIT(bi));

[Severity: Medium]
Can this result in an out-of-bounds bitwise shift on 32-bit architectures?

The BIT(bi) macro expands to (1UL << bi). On 32-bit systems, 1UL is 32
bits wide. If a module defines a classmap with 32 or more classes
(map->length >= 32), shifting by 32 or more triggers undefined behavior.

On most 32-bit architectures, the CPU masks the shift count modulo 32, meaning
BIT(32) evaluates to BIT(0). This causes the loop to incorrectly re-evaluate
and alter class 0 instead of processing the intended class, leading to
incorrect functional behavior when configuring dynamic debug.

> +		if (new_b == old_b)
>  			continue;
>  
>  		snprintf(query, QUERY_SIZE, "class %s %c%s", map->class_names[bi],

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721-dd-maint-2-v7-0-010fbe73b311@gmail.com?part=24