On Mon, Apr 08, 2024 at 11:01:54AM +0200, Marco Elver wrote:
> Add "new_exec" tracepoint, which is run right after the point of no
> return but before the current task assumes its new exec identity.
>
> Unlike the tracepoint "sched_process_exec", the "new_exec" tracepoint
> runs before flushing the old exec, i.e. while the task still has the
> original state (such as original MM), but when the new exec either
> succeeds or crashes (but never returns to the original exec).
>
> Being able to trace this event can be helpful in a number of use cases:
>
> * allowing tracing eBPF programs access to the original MM on exec,
> before current->mm is replaced;
> * counting exec in the original task (via perf event);
> * profiling flush time ("new_exec" to "sched_process_exec").
>
> Example of tracing output ("new_exec" and "sched_process_exec"):
>
> $ cat /sys/kernel/debug/tracing/trace_pipe
> <...>-379 [003] ..... 179.626921: new_exec: filename=/usr/bin/sshd pid=379 comm=sshd
> <...>-379 [003] ..... 179.629131: sched_process_exec: filename=/usr/bin/sshd pid=379 old_pid=379
> <...>-381 [002] ..... 180.048580: new_exec: filename=/bin/bash pid=381 comm=sshd
> <...>-381 [002] ..... 180.053122: sched_process_exec: filename=/bin/bash pid=381 old_pid=381
> <...>-385 [001] ..... 180.068277: new_exec: filename=/usr/bin/tty pid=385 comm=bash
> <...>-385 [001] ..... 180.069485: sched_process_exec: filename=/usr/bin/tty pid=385 old_pid=385
> <...>-389 [006] ..... 192.020147: new_exec: filename=/usr/bin/dmesg pid=389 comm=bash
> bash-389 [006] ..... 192.021377: sched_process_exec: filename=/usr/bin/dmesg pid=389 old_pid=389
>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> fs/exec.c | 2 ++
> include/trace/events/task.h | 30 ++++++++++++++++++++++++++++++
> 2 files changed, 32 insertions(+)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 38bf71cbdf5e..ab778ae1fc06 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1268,6 +1268,8 @@ int begin_new_exec(struct linux_binprm * bprm)
> if (retval)
> return retval;
>
> + trace_new_exec(current, bprm);
> +
All other steps in this function have explicit comments about
what/why/etc. Please add some kind of comment describing why the
tracepoint is where it is, etc.
For example, maybe something like:
/*
* Before any changes to 'current', report that the exec is about to
* happen (since we made it to the point of no return). On a successful
* exec, the 'sched_process_exec' tracepoint will also fire. On failure,
* ... [something else]
*/
> +TRACE_EVENT(new_exec,
> +
> + TP_PROTO(struct task_struct *task, struct linux_binprm *bprm),
> +
> + TP_ARGS(task, bprm),
> +
> + TP_STRUCT__entry(
> + __string( filename, bprm->filename )
> + __field( pid_t, pid )
> + __string( comm, task->comm )
> + ),
> +
> + TP_fast_assign(
> + __assign_str(filename, bprm->filename);
What about binfmt_misc, and binfmt_script? You may want bprm->interp
too?
-Kees
> + __entry->pid = task->pid;
> + __assign_str(comm, task->comm);
> + ),
> +
> + TP_printk("filename=%s pid=%d comm=%s",
> + __get_str(filename), __entry->pid, __get_str(comm))
> +);
> +
> #endif
>
> /* This part must be outside protection */
> --
> 2.44.0.478.gd926399ef9-goog
>
--
Kees Cook
