linux-kernel - Re: [PATCH v4 bpf-next 2/2] selftests/bpf: Add is_kernel parameter to LSM/bpf test programs

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Message-ID: <877c54jmjl.fsf@microsoft.com>
Date: Tue, 04 Mar 2025 17:25:50 -0800
From: Blaise Boscaccy <bboscaccy@...ux.microsoft.com>
To: Paul Moore <paul@...l-moore.com>
Cc: James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, Andrii
 Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, Yonghong
 Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, Stephen Smalley <stephen.smalley.work@...il.com>,
 Ondrej Mosnacek <omosnace@...hat.com>,
 linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH v4 bpf-next 2/2] selftests/bpf: Add is_kernel parameter
 to LSM/bpf test programs

Paul Moore <paul@...l-moore.com> writes:

> On Tue, Mar 4, 2025 at 3:31 PM Blaise Boscaccy
> <bboscaccy@...ux.microsoft.com> wrote:
>>
>> The security_bpf LSM hook now contains a boolean parameter specifying
>> whether an invocation of the bpf syscall originated from within the
>> kernel. Here, we update the function signature of relevant test
>> programs to include that new parameter.
>>
>> Signed-off-by: Blaise Boscaccy bboscaccy@...ux.microsoft.com
>> ---
>>  tools/testing/selftests/bpf/progs/rcu_read_lock.c           | 3 ++-
>>  tools/testing/selftests/bpf/progs/test_cgroup1_hierarchy.c  | 4 ++--
>>  tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c | 6 +++---
>>  tools/testing/selftests/bpf/progs/test_lookup_key.c         | 2 +-
>>  tools/testing/selftests/bpf/progs/test_ptr_untrusted.c      | 2 +-
>>  tools/testing/selftests/bpf/progs/test_task_under_cgroup.c  | 2 +-
>>  tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c   | 2 +-
>>  7 files changed, 11 insertions(+), 10 deletions(-)
>
> I see that Song requested that the changes in this patch be split out
> back in the v3 revision, will that cause git bisect issues if patch
> 1/2 is applied but patch 2/2 is not, or is there some BPF magic that
> ensures that the selftests will still run properly?
>

So there isn't any type checking in the bpf program's function
arguments against the LSM hook definitions, so it shouldn't cause any
build issues. To the best of my knowledge, the new is_kernel boolean
flag will end up living in r3. None of the current tests reference
that parameter, so if we bisected and ended up on the previous commit,
the bpf test programs would in a worst-case scenario simply clobber that
register, which shouldn't effect any test outcomes unless a test program
was somehow dependent on an uninitialized value in a scratch register. 

-blaise

> -- 
> paul-moore.com