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

[Kees Cook]

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?

>  #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