On Fri, Nov 03, 2017 at 10:03:17AM -0400, Steven Rostedt wrote: > On Thu, 2 Nov 2017 17:33:33 +0100 > Jessica Yu <j...@kernel.org> wrote: > > > Improve error handling when arming ftrace-based kprobes. Specifically, if > > we fail to arm a ftrace-based kprobe, register_kprobe()/enable_kprobe() > > should report an error instead of success. Previously, this has lead to > > confusing situations where register_kprobe() would return 0 indicating > > success, but the kprobe would not be functional if ftrace registration > > during the kprobe arming process had failed. We should therefore take any > > errors returned by ftrace into account and propagate this error so that we > > do not register/enable kprobes that cannot be armed. This can happen if, > > for example, register_ftrace_function() finds an IPMODIFY conflict (since > > kprobe_ftrace_ops has this flag set) and returns an error. Such a conflict > > is possible since livepatches also set the IPMODIFY flag for their > > ftrace_ops. > > > > arm_all_kprobes() keeps its current behavior and attempts to arm all > > kprobes. It returns the last encountered error and gives a warning if > > not all kprobes could be armed. > > > > This patch is based on Petr Mladek's original patchset (patches 2 and 3) > > back in 2015, which improved kprobes error handling, found here: > > > > https://lkml.org/lkml/2015/2/26/452 > > > > However, further work on this had been paused since then and the patches > > were not upstreamed. > > > > Based-on-patches-by: Petr Mladek <pmla...@suse.com> > > Signed-off-by: Jessica Yu <j...@kernel.org> > > --- > > kernel/kprobes.c | 88 > > ++++++++++++++++++++++++++++++++++++++++---------------- > > 1 file changed, 63 insertions(+), 25 deletions(-) > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index da2ccf142358..f4a094007cb5 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > @@ -978,18 +978,27 @@ static int prepare_kprobe(struct kprobe *p) > > } > > > > /* Caller must lock kprobe_mutex */ > > -static void arm_kprobe_ftrace(struct kprobe *p) > > +static int arm_kprobe_ftrace(struct kprobe *p) > > { > > - int ret; > > + int ret = 0; > > > > ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, > > (unsigned long)p->addr, 0, 0); > > - WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret); > > - kprobe_ftrace_enabled++; > > - if (kprobe_ftrace_enabled == 1) { > > + if (WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, > > ret)) > > + return ret; > > + > > + if (kprobe_ftrace_enabled == 0) { > > ret = register_ftrace_function(&kprobe_ftrace_ops); > > - WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret); > > + if (WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret)) > > + goto err_ftrace; > > } > > + > > + kprobe_ftrace_enabled++; > > + return ret; > > + > > +err_ftrace: > > + ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0); > > Hmm, this could have a very nasty side effect. If you remove a function > from the ops, and it was the last function, an empty ops means to trace > *all* functions.
But this error path only runs when register_ftrace_function() fails, in which case the ops aren't live anyway, right? -- Josh
