Re: [PATCH bpf-next v3 2/2] selftests/bpf: verify kallsyms entries for token-loaded subprograms

On Wed, 2026-04-15 at 19:17 +0000, [email protected] wrote:
> Sashiko AI review found 1 potential issue(s):
> - [Medium] Unchecked return values of `sysctl_set()` in `serial_test_token()` can lead to confusing test failures.
> --
> 
> commit e7dc629b9f37dc08742ff9bbddeaaf65c1e34956
> Author: Eduard Zingerman <[email protected]>
> 
> selftests/bpf: verify kallsyms entries for token-loaded subprograms
> 
> This commit adds a test to verify that both the main XDP program and its
> global subprogram appear in /proc/kallsyms when loaded using a user
> namespace BPF token. It also introduces a sysctl_set utility to configure
> system parameters needed to read kallsyms.
> 
> > diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
> > index b81dde283052e..cf5b94512cff4 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/token.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/token.c
> 
> [ ... ]
> 
> > @@ -1194,4 +1252,23 @@ void test_token(void)
> >  
> >  		subtest_userns(&opts, userns_bpf_token_info);
> >  	}
> > +	if (test__start_subtest("obj_priv_prog_kallsyms")) {
> > +		char perf_paranoid_orig[32] = {};
> > +		char kptr_restrict_orig[32] = {};
> > +		struct bpffs_opts opts = {
> > +			.cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD),
> > +			.progs = bit(BPF_PROG_TYPE_XDP),
> > +			.attachs = ~0ULL,
> > +		};
> > +
> > +		sysctl_set("/proc/sys/kernel/perf_event_paranoid", perf_paranoid_orig, "0");
> > +		sysctl_set("/proc/sys/kernel/kptr_restrict", kptr_restrict_orig, "0");
> 
> Should the return values of these sysctl_set calls be checked?
> 
> If the test is executed in an environment where these sysctls are read-only
> or inaccessible (such as inside a container), sysctl_set will silently fail.
> 
> This would cause load_kallsyms_local to read zeroed addresses because
> kptr_restrict wasn't successfully disabled, resulting in confusing test
> failures later at ASSERT_TRUE instead of catching the setup failure early.
> 
> Would it be better to wrap these with ASSERT_OK?

Makes sense.

> > +
> > +		subtest_userns(&opts, userns_obj_priv_prog_kallsyms);
> > +
> > +		if (perf_paranoid_orig[0])
> > +			sysctl_set("/proc/sys/kernel/perf_event_paranoid", NULL, perf_paranoid_orig);
> > +		if (kptr_restrict_orig[0])
> > +			sysctl_set("/proc/sys/kernel/kptr_restrict", NULL, kptr_restrict_orig);
> > +	}
> >  }