linux-kernel - Re: [PATCH bpf-next v4 06/12] bpf: selftests: Fix bpf_session

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Date: Tue, 18 Jun 2024 21:07:58 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Jiri Olsa <olsajiri@...il.com>, Daniel Xu <dxu@...uu.xyz>,
	shuah@...nel.org, ast@...nel.org, andrii@...nel.org,
	eddyz87@...il.com, daniel@...earbox.net, quentin@...valent.com,
	alan.maguire@...cle.com, acme@...nel.org, mykolal@...com,
	martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
	haoluo@...gle.com, bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: [PATCH bpf-next v4 06/12] bpf: selftests: Fix
 bpf_session_cookie() kfunc prototype

On Tue, Jun 18, 2024 at 09:58:23AM -0700, Andrii Nakryiko wrote:
> On Tue, Jun 18, 2024 at 5:43 AM Jiri Olsa <olsajiri@...il.com> wrote:
> >
> > On Mon, Jun 17, 2024 at 03:25:53PM -0700, Andrii Nakryiko wrote:
> > > On Mon, Jun 10, 2024 at 6:04 AM Jiri Olsa <olsajiri@...il.com> wrote:
> > > >
> > > > On Sat, Jun 08, 2024 at 03:16:02PM -0600, Daniel Xu wrote:
> > > > > The prototype defined in bpf_kfuncs.h was not in line with how the
> > > > > actual kfunc was defined. This causes compilation errors when kfunc
> > > > > prototypes are generated from BTF.
> > > > >
> > > > > Fix by aligning with actual kfunc definition.
> > > > >
> > > > > Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> > > > > ---
> > > > >  tools/testing/selftests/bpf/bpf_kfuncs.h                        | 2 +-
> > > > >  tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c | 2 +-
> > > > >  2 files changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > > > index be91a6919315..3b6675ab4086 100644
> > > > > --- a/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > > > +++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
> > > > > @@ -77,5 +77,5 @@ extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
> > > > >                                     struct bpf_key *trusted_keyring) __ksym;
> > > > >
> > > > >  extern bool bpf_session_is_return(void) __ksym __weak;
> > > > > -extern long *bpf_session_cookie(void) __ksym __weak;
> > > > > +extern __u64 *bpf_session_cookie(void) __ksym __weak;
> > > >
> > > > the original intent was to expose long instead of __u64 :-\
> > > >
> > >
> > > Cookies internally are always u64 (8 byte values). Marking them
> > > internally in the kernel as long could lead to problems on 32-bit
> > > architectures, potentially (it still needs to be 64-bit value
> > > according to BPF contract, but we'll allocate only 4 bytes for them).
> > >
> > > It seems better and safer to be explicit with __u64/u64 for cookies everywhere.
> >
> > hum, I based that on what we did for kprobe session,
> > but I guess it makes sense just for bpf side:
> 
> yep, exactly, long is 64-bit only for BPF "architecture", but
> internally it will be 4 bytes for 32-bit architectures, which will
> potentially lead to problems. With recent kfunc vmlinux.h generation,
> it's probably better to stick to explicitly sized types.

hm, it already got in 2b8dd87332cd, revert needs more changes in selftests
I'll send formal patch with fix below

jirka

---
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4b3fda456299..cd098846e251 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3530,7 +3530,7 @@ __bpf_kfunc bool bpf_session_is_return(void)
 	return session_ctx->is_return;
 }
 
-__bpf_kfunc long *bpf_session_cookie(void)
+__bpf_kfunc __u64 *bpf_session_cookie(void)
 {
 	struct bpf_session_run_ctx *session_ctx;
 
diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index be91a6919315..3b6675ab4086 100644
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -77,5 +77,5 @@ extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
 				      struct bpf_key *trusted_keyring) __ksym;
 
 extern bool bpf_session_is_return(void) __ksym __weak;
-extern long *bpf_session_cookie(void) __ksym __weak;
+extern __u64 *bpf_session_cookie(void) __ksym __weak;
 #endif
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c b/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
index d49070803e22..0835b5edf685 100644
--- a/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
@@ -25,7 +25,7 @@ int BPF_PROG(trigger)
 
 static int check_cookie(__u64 val, __u64 *result)
 {
-	long *cookie;
+	__u64 *cookie;
 
 	if (bpf_get_current_pid_tgid() >> 32 != pid)
 		return 1;