Re: [PATCH v6 10/12] tools/testing/selftests/bpf: make it adopt to task comm size change

[Yafang Shao]

On Tue, Oct 26, 2021 at 5:29 AM Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxx>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Petr Mladek <pmladek@xxxxxxxx>
> > ---
> >  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