From: Steven Rostedt rostedt@goodmis.org
The trace event verifier checks the formats of trace events to make sure that they do not point at memory that is not in the trace event itself or in data that will never be freed. If an event references data that was allocated when the event triggered and that same data is freed before the event is read, then the kernel can crash by reading freed memory.
The verifier runs at boot up (or module load) and scans the print formats of the events and checks their arguments to make sure that dereferenced pointers are safe. If the format uses "%*p.." the verifier will ignore it, and that could be dangerous. Cover this case as well.
Also add to the sample code a use case of "%*pbl".
Link: https://lore.kernel.org/all/bcba4d76-2c3f-4d11-baf0-02905db953dd@oracle.com/
Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers") Link: https://lore.kernel.org/20250327195311.2d89ec66@gandalf.local.home Reported-by: Libo Chen libo.chen@oracle.com Reviewed-by: Libo Chen libo.chen@oracle.com Tested-by: Libo Chen libo.chen@oracle.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/trace_events.c | 7 +++++++ samples/trace_events/trace-events-sample.h | 8 ++++++-- 2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 8638b7f7ff85..069e92856bda 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -470,6 +470,7 @@ static void test_event_printk(struct trace_event_call *call) case '%': continue; case 'p': + do_pointer: /* Find dereferencing fields */ switch (fmt[i + 1]) { case 'B': case 'R': case 'r': @@ -498,6 +499,12 @@ static void test_event_printk(struct trace_event_call *call) continue; if (fmt[i + j] == '*') { star = true; + /* Handle %*pbl case */ + if (!j && fmt[i + 1] == 'p') { + arg++; + i++; + goto do_pointer; + } continue; } if ((fmt[i + j] == 's')) { diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h index 999f78d380ae..1a05fc153353 100644 --- a/samples/trace_events/trace-events-sample.h +++ b/samples/trace_events/trace-events-sample.h @@ -319,7 +319,8 @@ TRACE_EVENT(foo_bar, __assign_cpumask(cpum, cpumask_bits(mask)); ),
- TP_printk("foo %s %d %s %s %s %s %s %s (%s) (%s) %s", __entry->foo, __entry->bar, + TP_printk("foo %s %d %s %s %s %s %s %s (%s) (%s) %s [%d] %*pbl", + __entry->foo, __entry->bar,
/* * Notice here the use of some helper functions. This includes: @@ -370,7 +371,10 @@ TRACE_EVENT(foo_bar,
__get_str(str), __get_str(lstr), __get_bitmask(cpus), __get_cpumask(cpum), - __get_str(vstr)) + __get_str(vstr), + __get_dynamic_array_len(cpus), + __get_dynamic_array_len(cpus), + __get_dynamic_array(cpus)) );
/*