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tracing: Add task_prctl_unknown tracepoint

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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@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/r/20241108113455.2924361-1-elver@google.com
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Marco Elver 2024-11-08 12:34:24 +01:00 • committed by Kees Cook
parent 4bbf9020be
commit c38904ebb7
2 changed files with 40 additions and 0 deletions
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37
include/trace/events/task.h
View file

@ -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 */

3
kernel/sys.c
View file

@ -75,6 +75,8 @@
#include <asm/io.h>
#include <asm/unistd.h>
#include <trace/events/task.h>
#include "uid16.h"
#ifndef SET_UNALIGN_CTL
@ -2810,6 +2812,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
error = arch_lock_shadow_stack_status(me, arg2);
break;
default:
trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
error = -EINVAL;
break;
}