netdev - [RFC PATCH bpf-next 2/3] tracing/kprobe: bpf: Compare instruction pointer with original one

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Message-Id: <151394274938.5598.2010794012082141248.stgit@devbox>
Date:   Fri, 22 Dec 2017 20:39:09 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Alexei Starovoitov <ast@...com>, Josef Bacik <jbacik@...com>
Cc:     rostedt@...dmis.org, mingo@...hat.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org, kernel-team@...com, daniel@...earbox.net,
        linux-btrfs@...r.kernel.org, darrick.wong@...cle.com,
        mhiramat@...nel.org, Josef Bacik <josef@...icpanda.com>
Subject: [RFC PATCH bpf-next 2/3] tracing/kprobe: bpf: Compare instruction pointer with original one

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 <mhiramat@...nel.org>
---
 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 d663660f8392..cefa9b0e396c 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_ftrace_kprobe_override_function(regs);
 	return 0;
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 265e3e27e8dc..a7c7035963f2 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;
@@ -1204,6 +1202,7 @@ 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);
@@ -1211,12 +1210,13 @@ 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)
@@ -1324,15 +1324,8 @@ 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;
 }