Re: [PATCH bpf-next v3 13/17] bpf: Report Program Structure CFG errors

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Tue Jul 14, 2026 at 10:00 PM CEST, Eduard Zingerman wrote:
> On Mon, 2026-07-13 at 17:39 +0200, Kumar Kartikeya Dwivedi wrote:
>> Augment selected subprogram CFG validation failures with Program Structure
>> reports. These errors are structural rather than path-dependent, so the report
>> focuses on source and instruction context instead of causal history.
>>
>> Cover jumps that leave the current subprogram, subprograms whose last
>> instruction can fall through into the next subprogram, and recursive bpf2bpf
>> call graph edges.
>>
>> Format long jump-range reasons directly in diagnostics.c, and keep the
>> fallthrough suggestion aligned with the verifier check by suggesting exit or
>> explicit jumps.
>>
>> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
>> ---
>>  kernel/bpf/cfg.c         | 55 ++++++++++++++++++++++++++++++++++++++++
>>  kernel/bpf/diagnostics.c | 19 ++++++++++++++
>>  kernel/bpf/diagnostics.h |  3 +++
>>  kernel/bpf/verifier.c    | 32 +++++++++++++++++++++++
>>  4 files changed, 109 insertions(+)
>>
>> diff --git a/kernel/bpf/cfg.c b/kernel/bpf/cfg.c
>> index 26d37066465f..376f6b6d469c 100644
>> --- a/kernel/bpf/cfg.c
>> +++ b/kernel/bpf/cfg.c
>> @@ -5,6 +5,8 @@
>>  #include <linux/filter.h>
>>  #include <linux/sort.h>
>>
>> +#include "diagnostics.h"
>> +
>>  #define verbose(env, fmt, args...) bpf_verifier_log_write(env, fmt, ##args)
>>
>>  /* non-recursive DFS pseudo code
>> @@ -113,6 +115,12 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env)
>>  	if (w < 0 || w >= env->prog->len) {
>>  		verbose_linfo(env, t, "%d: ", t);
>>  		verbose(env, "jump out of range from insn %d to %d\n", t, w);
>> +		bpf_diag_report_program_structure(env, t, "jump out of range",
>> +						  "Keep branch targets inside the program.",
>> +						  "Instruction %d jumps to instruction %d, but the "
>> +						  "program only contains instructions 0 through "
>> +						  "%d.",
>> +						  t, w, env->prog->len - 1);
>
> Nit: I'd forgo the formatting rules and just write the above like:
>
> 		bpf_diag_report_program_structure(
> 		  env, t, "jump out of range",
> 		  "Keep branch targets inside the program.",
> 		  "Instruction %d jumps to instruction %d, but the program only contains instructions 0 through %d.",
> 		   t, w, env->prog->len - 1);
>
>      Easier to read and easier to grep.
>
>>  		return -EINVAL;
>>  	}
>>
>

Ack, will change throughout the series.

> [...]