Re: [RFC bpf-next v3 06/11] bpf: validate value_type

[Martin KaFai Lau <martin.lau@linux.dev>]

On 9/20/23 8:59 AM, thinker.li@gmail.com wrote:
> From: Kui-Feng Lee <thinker.li@gmail.com>
> 
> A value_type should has three members; refcnt, state, and data.
> 
> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
> ---
>   kernel/bpf/bpf_struct_ops.c | 75 +++++++++++++++++++++++++++++++++++++
>   1 file changed, 75 insertions(+)
> 
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index ef8a1edec891..fb684d2ee99d 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -99,6 +99,79 @@ const struct bpf_prog_ops bpf_struct_ops_prog_ops = {
>   
>   static const struct btf_type *module_type;
>   
> +static bool check_value_member(struct btf *btf,
> +			       const struct btf_member *member,
> +			       int index,
> +			       const char *value_name,
> +			       const char *name, const char *type_name,
> +			       u16 kind)
> +{
> +	const char *mname, *mtname;
> +	const struct btf_type *mt;
> +	s32 mtype_id;
> +
> +	mname = btf_name_by_offset(btf, member->name_off);
> +	if (!*mname) {
> +		pr_warn("The member %d of %s should have a name\n",
> +			index, value_name);
> +		return false;
> +	}
> +	if (strcmp(mname, name)) {
> +		pr_warn("The member %d of %s should be refcnt\n",
> +			index, value_name);
> +		return false;
> +	}
> +	mtype_id = member->type;
> +	mt = btf_type_by_id(btf, mtype_id);
> +	mtname = btf_name_by_offset(btf, mt->name_off);
> +	if (!*mtname) {
> +		pr_warn("The type of the member %d of %s should have a name\n",
> +			index, value_name);
> +		return false;
> +	}
> +	if (strcmp(mtname, type_name)) {
> +		pr_warn("The type of the member %d of %s should be refcount_t\n",
> +			index, value_name);
> +		return false;
> +	}
> +	if (btf_kind(mt) != kind) {
> +		pr_warn("The type of the member %d of %s should be %d\n",
> +			index, value_name, btf_kind(mt));
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +static bool is_valid_value_type(struct btf *btf, s32 value_id,
> +				const char *type_name, const char *value_name)
> +{
> +	const struct btf_member *member;
> +	const struct btf_type *vt;
> +
> +	vt = btf_type_by_id(btf, value_id);
> +	if (btf_vlen(vt) != 3) {
> +		pr_warn("The number of %s's members should be 3, but we get %d\n",
> +			value_name, btf_vlen(vt));
> +		return false;
> +	}
> +	member = btf_type_member(vt);
> +	if (!check_value_member(btf, member, 0, value_name,
> +				"refcnt", "refcount_t", BTF_KIND_TYPEDEF))
> +		return false;
> +	member++;
> +	if (!check_value_member(btf, member, 1, value_name,
> +				"state", "bpf_struct_ops_state",
> +				BTF_KIND_ENUM))
> +		return false;
> +	member++;

I wonder if giving BPF_STRUCT_OPS_COMMON_VALUE a proper struct will make the 
validation cleaner. Like,

struct bpf_struct_ops_common {
	refcount_t refcnt;
	enum bpf_struct_ops_state state;
};

wdyt?

> +	if (!check_value_member(btf, member, 2, value_name,
> +				"data", type_name, BTF_KIND_STRUCT))

Instead of checking name, I think this can directly check with the st_ops->type.

> +		return false;
> +
> +	return true;
> +}