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. -- 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
