On Fri, 19 Aug 2022 21:40:39 -0400 Steven Rostedt rostedt@goodmis.org wrote:

From: "Steven Rostedt (Google)" rostedt@goodmis.org

Currently, if a symbol "@" is attempted to be used with an event probe (eprobes), it will cause a NULL pointer dereference crash.

Both kprobes and uprobes can reference data other than the main registers. Such as immediate address, symbols and the current task name. Have eprobes do the same thing.

For "comm", if "comm" is used and the event being attached to does not have the "comm" field, then make it the "$comm" that kprobes has. This is consistent to the way histograms and filters work.

Hmm, I think I would better allow user to use $COMM to get comm string for kprobe/uprobe event users too. (There are many special variables...) Anyway, this looks good to me.

Acked-by: Masami Hiramatsu (Google) mhiramat@kernel.org

Thank you!

Cc: stable@vger.kernel.org Fixes: 7491e2c44278 ("tracing: Add a probe that attaches to trace events") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org

---

kernel/trace/trace_eprobe.c | 67 +++++++++++++++++++++++++++++++++---- 1 file changed, 61 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c index a1d3423ab74f..63218a541217 100644 --- a/kernel/trace/trace_eprobe.c +++ b/kernel/trace/trace_eprobe.c @@ -227,6 +227,7 @@ static int trace_eprobe_tp_arg_update(struct trace_eprobe *ep, int i) struct probe_arg *parg = &ep->tp.args[i]; struct ftrace_event_field *field; struct list_head *head;

• int ret = -ENOENT;

head = trace_get_fields(ep->event); list_for_each_entry(field, head, link) { @@ -236,9 +237,17 @@ static int trace_eprobe_tp_arg_update(struct trace_eprobe *ep, int i) return 0; } }

• /* Argument no found on event. But allow for comm and COMM to be used */
• if (strcmp(parg->code->data, "COMM") == 0 ||

•    strcmp(parg->code->data, "comm") == 0) {
  

• parg->code->op = FETCH_OP_COMM;
  

• ret = 0;
  

• }
• kfree(parg->code->data); parg->code->data = NULL;

• return -ENOENT;

• return ret;

} static int eprobe_event_define_fields(struct trace_event_call *event_call) @@ -363,16 +372,38 @@ static unsigned long get_event_field(struct fetch_insn *code, void *rec) static int get_eprobe_size(struct trace_probe *tp, void *rec) {

• struct fetch_insn *code; struct probe_arg *arg; int i, len, ret = 0;

for (i = 0; i < tp->nr_args; i++) { arg = tp->args + i;

• if (unlikely(arg->dynamic)) {
  

• if (arg->dynamic) {
  unsigned long val;
  

• 	val = get_event_field(arg->code, rec);
  

• 	len = process_fetch_insn_bottom(arg->code + 1, val, NULL, NULL);
  

• 	code = arg->code;
  

• retry:

• 	switch (code->op) {
  

• 	case FETCH_OP_TP_ARG:
  

• 		val = get_event_field(code, rec);
  

• 		break;
  

• 	case FETCH_OP_IMM:
  

• 		val = code->immediate;
  

• 		break;
  

• 	case FETCH_OP_COMM:
  

• 		val = (unsigned long)current->comm;
  

• 		break;
  

• 	case FETCH_OP_DATA:
  

• 		val = (unsigned long)code->data;
  

• 		break;
  

• 	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
  

• 		code++;
  

• 		goto retry;
  

• 	default:
  

• 		continue;
  

• 	}
  

• 	code++;
  

• 	len = process_fetch_insn_bottom(code, val, NULL, NULL);
  if (len > 0)
  	ret += len;
  

  }

@@ -390,8 +421,28 @@ process_fetch_insn(struct fetch_insn *code, void *rec, void *dest, { unsigned long val;

• val = get_event_field(code, rec);
• return process_fetch_insn_bottom(code + 1, val, dest, base);

• retry:
• switch (code->op) {
• case FETCH_OP_TP_ARG:

• val = get_event_field(code, rec);
  

• break;
  

• case FETCH_OP_IMM:

• val = code->immediate;
  

• break;
  

• case FETCH_OP_COMM:

• val = (unsigned long)current->comm;
  

• break;
  

• case FETCH_OP_DATA:

• val = (unsigned long)code->data;
  

• break;
  

• case FETCH_NOP_SYMBOL: /* Ignore a place holder */

• code++;
  

• goto retry;
  

• default:

• return -EILSEQ;
  

• }
• code++;
• return process_fetch_insn_bottom(code, val, dest, base);

} NOKPROBE_SYMBOL(process_fetch_insn) @@ -866,6 +917,10 @@ static int trace_eprobe_tp_update_arg(struct trace_eprobe *ep, const char *argv[ trace_probe_log_err(0, BAD_ATTACH_ARG); }

• /* Handle symbols "@" */
• if (!ret)

• ret = traceprobe_update_arg(&ep->tp.args[i]);
  

• return ret;

} -- 2.35.1