Date:   Tue, 26 Oct 2021 10:21:43 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Valentin Schneider <valentin.schneider@....com>,
        Qiang Zhang <qiang.zhang@...driver.com>,
        robdclark <robdclark@...omium.org>,
        christian <christian@...uner.io>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        dennis.dalessandro@...nelisnetworks.com,
        mike.marciniszyn@...nelisnetworks.com, dledford@...hat.com,
        jgg@...pe.ca, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH v6 10/12] tools/testing/selftests/bpf: make it adopt to
 task comm size change

On Tue, Oct 26, 2021 at 5:29 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Oct 25, 2021 at 08:33:13AM +0000, Yafang Shao wrote:
> > The hard-coded 16 is used in various bpf progs. These progs get task
> > comm either via bpf_get_current_comm() or prctl() or
> > bpf_core_read_str(), all of which can work well even if the task comm size
> > is changed.
> >
> > In these BPF programs, one thing to be improved is the
> > sched:sched_switch tracepoint args. As the tracepoint args are derived
> > from the kernel, we'd better make it same with the kernel. So the macro
> > TASK_COMM_LEN is converted to type enum, then all the BPF programs can
> > get it through BTF.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> >  include/linux/sched.h                                   | 9 +++++++--
> >  tools/testing/selftests/bpf/progs/test_stacktrace_map.c | 6 +++---
> >  tools/testing/selftests/bpf/progs/test_tracepoint.c     | 6 +++---
> >  3 files changed, 13 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index c1a927ddec64..124538db792c 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -274,8 +274,13 @@ struct task_group;
> >
> >  #define get_current_state()  READ_ONCE(current->__state)
> >
> > -/* Task command name length: */
> > -#define TASK_COMM_LEN                        16
> > +/*
> > + * Define the task command name length as enum, then it can be visible to
> > + * BPF programs.
> > + */
> > +enum {
> > +     TASK_COMM_LEN = 16,
> > +};
> >
> >  extern void scheduler_tick(void);
> >
> > diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> > index 00ed48672620..e9b602a6dc1b 100644
> > --- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> > +++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> > @@ -1,7 +1,7 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  // Copyright (c) 2018 Facebook
> >
> > -#include <linux/bpf.h>
> > +#include <vmlinux.h>
>
> Why is this change needed here and below?
>

If the BPF programs want to use the type defined in the kernel, for
example the enum we used here, we must include the vmlinux.h generated
by BTF.

> >  #include <bpf/bpf_helpers.h>
> >
> >  #ifndef PERF_MAX_STACK_DEPTH
> > @@ -41,11 +41,11 @@ struct {
> >  /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
> >  struct sched_switch_args {
> >       unsigned long long pad;
> > -     char prev_comm[16];
> > +     char prev_comm[TASK_COMM_LEN];
> >       int prev_pid;
> >       int prev_prio;
> >       long long prev_state;
> > -     char next_comm[16];
> > +     char next_comm[TASK_COMM_LEN];
> >       int next_pid;
> >       int next_prio;
> >  };
> > diff --git a/tools/testing/selftests/bpf/progs/test_tracepoint.c b/tools/testing/selftests/bpf/progs/test_tracepoint.c
> > index 4b825ee122cf..f21982681e28 100644
> > --- a/tools/testing/selftests/bpf/progs/test_tracepoint.c
> > +++ b/tools/testing/selftests/bpf/progs/test_tracepoint.c
> > @@ -1,17 +1,17 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  // Copyright (c) 2017 Facebook
> >
> > -#include <linux/bpf.h>
> > +#include <vmlinux.h>
> >  #include <bpf/bpf_helpers.h>
> >
> >  /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
> >  struct sched_switch_args {
> >       unsigned long long pad;
> > -     char prev_comm[16];
> > +     char prev_comm[TASK_COMM_LEN];
> >       int prev_pid;
> >       int prev_prio;
> >       long long prev_state;
> > -     char next_comm[16];
> > +     char next_comm[TASK_COMM_LEN];
> >       int next_pid;
> >       int next_prio;
> >  };
> > --
> > 2.17.1
> >
>
> --
> Kees Cook



-- 
Thanks
Yafang

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