Re: [PATCH bpf-next 1/3] bpf: Add support for bpf_get_func_ip helper for uprobe program

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Aug 02, 2023 at 12:21:59PM +0100, Alan Maguire wrote:

SNIP

> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index c92eb8c6ff08..7930a91ca7f3 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1057,9 +1057,28 @@ static unsigned long get_entry_ip(unsigned long fentry_ip)
> >  #define get_entry_ip(fentry_ip) fentry_ip
> >  #endif
> >  
> > +#ifdef CONFIG_UPROBES
> > +static unsigned long bpf_get_func_ip_uprobe(struct pt_regs *regs)
> > +{
> > +	struct uprobe_dispatch_data *udd;
> > +
> > +	udd = (struct uprobe_dispatch_data *) current->utask->vaddr;
> > +	return udd->bp_addr;
> > +}
> > +#else
> > +#define bpf_get_func_ip_uprobe(regs) (u64) -1
> 
> Small thing - I don't think this value is exposed to users due to the
> run_ctx->is_uprobe predicate, but would it be worth using -EOPNOTSUPP
> here maybe?

I initially thought of putting WARN_ON_ONCE in here, but as you said it
won't trigger so ended up with -1 .. but I don't mind using -EOPNOTSUPP

jirka

> 
> > +#endif
> > +
> >  BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> >  {
> > -	struct kprobe *kp = kprobe_running();
> > +	struct bpf_trace_run_ctx *run_ctx;
> > +	struct kprobe *kp;
> > +
> > +	run_ctx = container_of(current->bpf_ctx, struct bpf_trace_run_ctx, run_ctx);
> > +	if (run_ctx->is_uprobe)
> > +		return bpf_get_func_ip_uprobe(regs);
> > +
> > +	kp = kprobe_running();
> >  
> >  	if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
> >  		return 0;
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index 01ea148723de..7dde806be91e 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -519,3 +519,8 @@ void __trace_probe_log_err(int offset, int err);
> >  
> >  #define trace_probe_log_err(offs, err)	\
> >  	__trace_probe_log_err(offs, TP_ERR_##err)
> > +
> > +struct uprobe_dispatch_data {
> > +	struct trace_uprobe	*tu;
> > +	unsigned long		bp_addr;
> > +};
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index 555c223c3232..fc76c3985672 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -88,11 +88,6 @@ static struct trace_uprobe *to_trace_uprobe(struct dyn_event *ev)
> >  static int register_uprobe_event(struct trace_uprobe *tu);
> >  static int unregister_uprobe_event(struct trace_uprobe *tu);
> >  
> > -struct uprobe_dispatch_data {
> > -	struct trace_uprobe	*tu;
> > -	unsigned long		bp_addr;
> > -};
> > -
> >  static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs);
> >  static int uretprobe_dispatcher(struct uprobe_consumer *con,
> >  				unsigned long func, struct pt_regs *regs);
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index 70da85200695..d21deb46f49f 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -5086,9 +5086,14 @@ union bpf_attr {
> >   * u64 bpf_get_func_ip(void *ctx)
> >   * 	Description
> >   * 		Get address of the traced function (for tracing and kprobe programs).
> > + *
> > + * 		When called for kprobe program attached as uprobe it returns
> > + * 		probe address for both entry and return uprobe.
> > + *
> >   * 	Return
> > - * 		Address of the traced function.
> > + * 		Address of the traced function for kprobe.
> >   * 		0 for kprobes placed within the function (not at the entry).
> > + * 		Address of the probe for uprobe and return uprobe.
> >   *
> >   * u64 bpf_get_attach_cookie(void *ctx)
> >   * 	Description