[ Added Andrew Morton too ] On Tue, 27 Mar 2018 15:00:41 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Tue, 27 Mar 2018 11:45:34 -0700 > Alexei Starovoitov <ast@xxxxxx> wrote: > > > >> + > > >> + snprintf(buf, sizeof(buf), "__bpf_trace_%s", tp->name); > > >> + addr = kallsyms_lookup_name(buf); > > >> + if (!addr) > > >> + return -ENOENT; > > >> + > > >> + return tracepoint_probe_register(tp, (void *)addr, prog); > > > > > > You are putting in a hell of a lot of trust with kallsyms returning > > > properly. I can see this being very fragile. This is calling a function > > > based on the result of kallsyms. I'm sure the security folks would love > > > this. > > > > > > There's a few things to make this a bit more robust. One is to add a > > > table that points to all __bpf_trace_* functions, and verify that the > > > result from kallsyms is in that table. > > > > > > Honestly, I think this is too much of a short cut and a hack. I know > > > you want to keep it "simple" and save space, but you really should do > > > it the same way ftrace and perf do it. That is, create a section and > > > have all tracepoints create a structure that holds a pointer to the > > > tracepoint and to the bpf probe function. Then you don't even need the > > > kernel_tracepoint_find_by_name(), you just iterate over your table and > > > you get the tracepoint and the bpf function associated to it. > > > > > > Relying on kallsyms to return an address to execute is just way too > > > extreme and fragile for my liking. > > > > Wasting extra 8bytes * number_of_tracepoints just for lack of trust > > in kallsyms doesn't sound like good trade off to me. > > If kallsyms are inaccurate all sorts of things will break: > > kprobes, livepatch, etc. > > I'd rather suggest for ftrace to use kallsyms approach as well > > and reduce memory footprint. > > If Linus, Thomas, Peter, Ingo, and the security folks trust kallsyms to > return a valid function pointer from a name, then sure, we can try > going that way. I would like an ack from Linus and/or Andrew before we go further down this road. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
