Re: [PATCH v2 bpf-next 4/9] btf: support kernel parsing of BTF with kind layout

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Jun 16, 2023 at 06:17:22PM +0100, Alan Maguire wrote:

SNIP

>  static int btf_sec_info_cmp(const void *a, const void *b)
> @@ -5193,32 +5246,37 @@ static int btf_check_sec_info(struct btf_verifier_env *env,
>  			      u32 btf_data_size)
>  {
>  	struct btf_sec_info secs[ARRAY_SIZE(btf_sec_info_offset)];
> -	u32 total, expected_total, i;
> +	u32 nr_secs = ARRAY_SIZE(btf_sec_info_offset);
> +	u32 total, expected_total, gap, i;
>  	const struct btf_header *hdr;
>  	const struct btf *btf;
>  
>  	btf = env->btf;
>  	hdr = &btf->hdr;
>  
> +	if (hdr->hdr_len < sizeof(struct btf_header))
> +		nr_secs--;
> +
>  	/* Populate the secs from hdr */
> -	for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++)
> +	for (i = 0; i < nr_secs; i++)
>  		secs[i] = *(struct btf_sec_info *)((void *)hdr +
>  						   btf_sec_info_offset[i]);
>  
> -	sort(secs, ARRAY_SIZE(btf_sec_info_offset),
> +	sort(secs, nr_secs,
>  	     sizeof(struct btf_sec_info), btf_sec_info_cmp, NULL);
>  
>  	/* Check for gaps and overlap among sections */
>  	total = 0;
>  	expected_total = btf_data_size - hdr->hdr_len;
> -	for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++) {
> +	for (i = 0; i < nr_secs; i++) {
>  		if (expected_total < secs[i].off) {
>  			btf_verifier_log(env, "Invalid section offset");
>  			return -EINVAL;
>  		}
> -		if (total < secs[i].off) {
> -			/* gap */
> -			btf_verifier_log(env, "Unsupported section found");
> +		gap = secs[i].off - total;
> +		if (gap >= 4) {
> +			/* gap larger than alignment gap */
> +			btf_verifier_log(env, "Unsupported section gap found");
>  			return -EINVAL;

this sems to break several btf header tests with:

	do_test_raw:PASS:check 0 nsec
	do_test_raw:FAIL:check expected err_str:Unsupported section found

	magic: 0xeb9f
	version: 1
	flags: 0x0
	hdr_len: 40
	type_off: 4
	type_len: 16
	str_off: 16
	str_len: 5
	btf_total_size: 61
	Unsupported section gap found
	#23/48   btf/btf_header test. Gap between hdr and type:FAIL


jirka

>  		}
>  		if (total > secs[i].off) {
> @@ -5230,7 +5288,7 @@ static int btf_check_sec_info(struct btf_verifier_env *env,
>  					 "Total section length too long");
>  			return -EINVAL;
>  		}
> -		total += secs[i].len;
> +		total += secs[i].len + gap;
>  	}
>  
>  	/* There is data other than hdr and known sections */
> @@ -5293,7 +5351,7 @@ static int btf_parse_hdr(struct btf_verifier_env *env)
>  		return -ENOTSUPP;
>  	}
>  
> -	if (hdr->flags) {
> +	if (hdr->flags & ~(BTF_FLAG_CRC_SET | BTF_FLAG_BASE_CRC_SET)) {
>  		btf_verifier_log(env, "Unsupported flags");
>  		return -ENOTSUPP;
>  	}
> @@ -5530,6 +5588,10 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
>  	if (err)
>  		goto errout;
>  
> +	err = btf_parse_kind_layout_sec(env);
> +	if (err)
> +		goto errout;
> +
>  	err = btf_parse_type_sec(env);
>  	if (err)
>  		goto errout;
> -- 
> 2.39.3
>