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. Perhaps you want to add it to the "notrace" list. Which would require implementing a ftrace_set_notrace_ip() function. Which I believe is what you want. Any function in the notrace hash will have the same functions in the filter hash be ignored. I'll let Masami review the rest. -- Steve > + return ret; > } >
