linux-kernel - Re: [PATCH v3 1/2] tracing: Add task_prctl

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Message-ID: <CANpmjNPuXxa3=SDZ_0uQ+ez2Tis96C2B-nE4NJSvCs4LBjjQgA@mail.gmail.com>
Date: Fri, 15 Nov 2024 13:00:00 +0100
From: Marco Elver <elver@...gle.com>
To: elver@...gle.com, Steven Rostedt <rostedt@...dmis.org>, 
	Kees Cook <keescook@...omium.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 1/2] tracing: Add task_prctl_unknown tracepoint

On Fri, 8 Nov 2024 at 12:35, Marco Elver <elver@...gle.com> wrote:
>
> prctl() is a complex syscall which multiplexes its functionality based
> on a large set of PR_* options. Currently we count 64 such options. The
> return value of unknown options is -EINVAL, and doesn't distinguish from
> known options that were passed invalid args that also return -EINVAL.
>
> To understand if programs are attempting to use prctl() options not yet
> available on the running kernel, provide the task_prctl_unknown
> tracepoint.
>
> Note, this tracepoint is in an unlikely cold path, and would therefore
> be suitable for continuous monitoring (e.g. via perf_event_open).
>
> While the above is likely the simplest usecase, additionally this
> tracepoint can help unlock some testing scenarios (where probing
> sys_enter or sys_exit causes undesirable performance overheads):
>
>   a. unprivileged triggering of a test module: test modules may register a
>      probe to be called back on task_prctl_unknown, and pick a very large
>      unknown prctl() option upon which they perform a test function for an
>      unprivileged user;
>
>   b. unprivileged triggering of an eBPF program function: similar
>      as idea (a).
>
> Example trace_pipe output:
>
>   test-380     [001] .....    78.142904: task_prctl_unknown: option=1234 arg2=101 arg3=102 arg4=103 arg5=104
>
> Signed-off-by: Marco Elver <elver@...gle.com>

Steven, unless there are any further objections, would you be able to
take this through the tracing tree?

Many thanks!

> ---
> v3:
> * Remove "comm".
>
> v2:
> * Remove "pid" in trace output (suggested by Steven).
> ---
>  include/trace/events/task.h | 37 +++++++++++++++++++++++++++++++++++++
>  kernel/sys.c                |  3 +++
>  2 files changed, 40 insertions(+)
>
> diff --git a/include/trace/events/task.h b/include/trace/events/task.h
> index 47b527464d1a..209d315852fb 100644
> --- a/include/trace/events/task.h
> +++ b/include/trace/events/task.h
> @@ -56,6 +56,43 @@ TRACE_EVENT(task_rename,
>                 __entry->newcomm, __entry->oom_score_adj)
>  );
>
> +/**
> + * task_prctl_unknown - called on unknown prctl() option
> + * @option:    option passed
> + * @arg2:      arg2 passed
> + * @arg3:      arg3 passed
> + * @arg4:      arg4 passed
> + * @arg5:      arg5 passed
> + *
> + * Called on an unknown prctl() option.
> + */
> +TRACE_EVENT(task_prctl_unknown,
> +
> +       TP_PROTO(int option, unsigned long arg2, unsigned long arg3,
> +                unsigned long arg4, unsigned long arg5),
> +
> +       TP_ARGS(option, arg2, arg3, arg4, arg5),
> +
> +       TP_STRUCT__entry(
> +               __field(        int,            option)
> +               __field(        unsigned long,  arg2)
> +               __field(        unsigned long,  arg3)
> +               __field(        unsigned long,  arg4)
> +               __field(        unsigned long,  arg5)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->option = option;
> +               __entry->arg2 = arg2;
> +               __entry->arg3 = arg3;
> +               __entry->arg4 = arg4;
> +               __entry->arg5 = arg5;
> +       ),
> +
> +       TP_printk("option=%d arg2=%ld arg3=%ld arg4=%ld arg5=%ld",
> +                 __entry->option, __entry->arg2, __entry->arg3, __entry->arg4, __entry->arg5)
> +);
> +
>  #endif
>
>  /* This part must be outside protection */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 4da31f28fda8..b366cef102ec 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -75,6 +75,8 @@
>  #include <asm/io.h>
>  #include <asm/unistd.h>
>
> +#include <trace/events/task.h>
> +
>  #include "uid16.h"
>
>  #ifndef SET_UNALIGN_CTL
> @@ -2785,6 +2787,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>                 error = RISCV_SET_ICACHE_FLUSH_CTX(arg2, arg3);
>                 break;
>         default:
> +               trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
>                 error = -EINVAL;
>                 break;
>         }
> --
> 2.47.0.277.g8800431eea-goog
>