[PATCH bpf-next v5 2/5] tracing/kprobe: bpf: Compare instruction pointer with original one

[Masami Hiramatsu]

Compare instruction pointer with original one on the
stack instead using per-cpu bpf_kprobe_override flag.

This patch also consolidates reset_current_kprobe() and
preempt_enable_no_resched() blocks. Those can be done
in one place.

Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
Reviewed-by: Josef Bacik <jba...@fb.com>
---
 kernel/trace/bpf_trace.c    |    1 -
 kernel/trace/trace_kprobe.c |   21 +++++++--------------
 2 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 1966ad3bf3e0..24ed6363e00f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -83,7 +83,6 @@ EXPORT_SYMBOL_GPL(trace_call_bpf);
 #ifdef CONFIG_BPF_KPROBE_OVERRIDE
 BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc)
 {
-       __this_cpu_write(bpf_kprobe_override, 1);
        regs_set_return_value(regs, rc);
        arch_kprobe_override_function(regs);
        return 0;
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3c8deb977a8b..b8c90441bc87 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -42,8 +42,6 @@ struct trace_kprobe {
        (offsetof(struct trace_kprobe, tp.args) +       \
        (sizeof(struct probe_arg) * (n)))
 
-DEFINE_PER_CPU(int, bpf_kprobe_override);
-
 static nokprobe_inline bool trace_kprobe_is_return(struct trace_kprobe *tk)
 {
        return tk->rp.handler != NULL;
@@ -1205,6 +1203,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs 
*regs)
        int rctx;
 
        if (bpf_prog_array_valid(call)) {
+               unsigned long orig_ip = instruction_pointer(regs);
                int ret;
 
                ret = trace_call_bpf(call, regs);
@@ -1212,12 +1211,13 @@ kprobe_perf_func(struct trace_kprobe *tk, struct 
pt_regs *regs)
                /*
                 * We need to check and see if we modified the pc of the
                 * pt_regs, and if so clear the kprobe and return 1 so that we
-                * don't do the instruction skipping.  Also reset our state so
-                * we are clean the next pass through.
+                * don't do the single stepping.
+                * The ftrace kprobe handler leaves it up to us to re-enable
+                * preemption here before returning if we've modified the ip.
                 */
-               if (__this_cpu_read(bpf_kprobe_override)) {
-                       __this_cpu_write(bpf_kprobe_override, 0);
+               if (orig_ip != instruction_pointer(regs)) {
                        reset_current_kprobe();
+                       preempt_enable_no_resched();
                        return 1;
                }
                if (!ret)
@@ -1325,15 +1325,8 @@ static int kprobe_dispatcher(struct kprobe *kp, struct 
pt_regs *regs)
        if (tk->tp.flags & TP_FLAG_TRACE)
                kprobe_trace_func(tk, regs);
 #ifdef CONFIG_PERF_EVENTS
-       if (tk->tp.flags & TP_FLAG_PROFILE) {
+       if (tk->tp.flags & TP_FLAG_PROFILE)
                ret = kprobe_perf_func(tk, regs);
-               /*
-                * The ftrace kprobe handler leaves it up to us to re-enable
-                * preemption here before returning if we've modified the ip.
-                */
-               if (ret)
-                       preempt_enable_no_resched();
-       }
 #endif
        return ret;
 }