Re: [PATCH bpf-next 04/10] bpf: remember if bpf_map was unprivileged and use that consistently

[Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>]

On Tue, May 02, 2023 at 04:06:13PM -0700, Andrii Nakryiko wrote:
>  }
>  
> -static struct bpf_map *array_map_alloc(union bpf_attr *attr)
> +static u32 array_index_mask(u32 max_entries)
>  {
> -	bool percpu = attr->map_type == BPF_MAP_TYPE_PERCPU_ARRAY;
> -	int numa_node = bpf_map_attr_numa_node(attr);
> -	u32 elem_size, index_mask, max_entries;
> -	bool bypass_spec_v1 = bpf_bypass_spec_v1();

static inline bool bpf_bypass_spec_v1(void)
{
        return perfmon_capable();
}

> +		/* unprivileged is OK, but we still record if we had CAP_BPF */
> +		unpriv = !bpf_capable();

map->unpriv flag makes sense as !CAP_BPF,
but it's not equivalent to bpf_bypass_spec_v1.

>  		break;
>  	default:
>  		WARN(1, "unsupported map type %d", map_type);
>  		return -EPERM;
>  	}
>  
> +	/* ARRAY-like maps have special sizing provisions for mitigating Spectre v1 */
> +	if (unpriv) {
> +		switch (map_type) {
> +		case BPF_MAP_TYPE_ARRAY:
> +		case BPF_MAP_TYPE_PERCPU_ARRAY:
> +		case BPF_MAP_TYPE_PROG_ARRAY:
> +		case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
> +		case BPF_MAP_TYPE_CGROUP_ARRAY:
> +		case BPF_MAP_TYPE_ARRAY_OF_MAPS:
> +			err = bpf_array_adjust_for_spec_v1(attr);
> +			if (err)
> +				return err;
> +			break;
> +		}
> +	}
> +
>  	map = ops->map_alloc(attr);
>  	if (IS_ERR(map))
>  		return PTR_ERR(map);
>  	map->ops = ops;
>  	map->map_type = map_type;
> +	map->unpriv = unpriv;
>  
>  	err = bpf_obj_name_cpy(map->name, attr->map_name,
>  			       sizeof(attr->map_name));
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index ff4a8ab99f08..481aaf189183 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -8731,11 +8731,9 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
>  	}
>  
>  	if (!BPF_MAP_PTR(aux->map_ptr_state))
> -		bpf_map_ptr_store(aux, meta->map_ptr,
> -				  !meta->map_ptr->bypass_spec_v1);
> +		bpf_map_ptr_store(aux, meta->map_ptr, meta->map_ptr->unpriv);
>  	else if (BPF_MAP_PTR(aux->map_ptr_state) != meta->map_ptr)
> -		bpf_map_ptr_store(aux, BPF_MAP_PTR_POISON,
> -				  !meta->map_ptr->bypass_spec_v1);
> +		bpf_map_ptr_store(aux, BPF_MAP_PTR_POISON, meta->map_ptr->unpriv);
>  	return 0;
>  }
>  
> -- 
> 2.34.1
>