Re: [PATCH bpf-next] selftests/bpf: veristat: Minimize map size during verification

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Setting `max_entries` to 1 for `BPF_MAP_TYPE_RHASH` maps causes map creation to fail if `map_extra` > 1.
--

--- Patch [1]: [PATCH bpf-next] selftests/bpf: veristat: Minimize map size during verification ---
commit a11623d3f77bb05764867d10c3ff357f2a8a1403
Author: Emil Tsalapatis <emil@etsalapatis.com>

selftests/bpf: veristat: Minimize map size during verification

The veristat tool loads objects and maps into the kernel to verify them.
This patch expands veristat to resize maps whose max_entries are not
relevant to verification to as low as possible to avoid -ENOMEM errors
on smaller test machines.

> diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
> index a7db6f04f7e14..8d374e1406532 100644
> --- a/tools/testing/selftests/bpf/veristat.c
> +++ b/tools/testing/selftests/bpf/veristat.c
[ ... ]
> @@ -1248,6 +1263,37 @@ static void fixup_obj_maps(struct bpf_object *obj)
>  
>  		/* fix up map size, if necessary */
>  		switch (bpf_map__type(map)) {
> +		/*
> +		 * if the verifier doesn't use max_entries
> +		 * then set to 1 to avoid -ENOMEM
> +		 */
> +		case BPF_MAP_TYPE_HASH:
> +		case BPF_MAP_TYPE_PERCPU_HASH:
> +		case BPF_MAP_TYPE_LRU_HASH:
> +		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
> +		case BPF_MAP_TYPE_HASH_OF_MAPS:
> +		case BPF_MAP_TYPE_RHASH:
> +		case BPF_MAP_TYPE_SOCKHASH:
> +		case BPF_MAP_TYPE_DEVMAP_HASH:
> +		case BPF_MAP_TYPE_LPM_TRIE:
> +		case BPF_MAP_TYPE_QUEUE:
> +		case BPF_MAP_TYPE_STACK:
> +		case BPF_MAP_TYPE_BLOOM_FILTER:
> +		case BPF_MAP_TYPE_STACK_TRACE:
> +			bpf_map__set_max_entries(map, 1);
> +			break;

[Severity: Medium]
Will setting max_entries to 1 cause map creation to fail for
BPF_MAP_TYPE_RHASH maps that have map_extra set to greater than 1?

The kernel's rhtab_map_alloc_check() enforces that map_extra must be less
than or equal to max_entries. If a BPF program legitimately uses an RHASH
map with a map_extra preallocation hint greater than 1, this unconditional
minimization will cause an -EINVAL load failure, making veristat erroneously
report a verification failure.

Does veristat also need to adjust map_extra when reducing max_entries for
RHASH maps?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260706225052.35543-1-emil@etsalapatis.com?part=1