linux-kernel - [RFC PATCH bpf-next 1/3] tracing/kprobe: bpf: Check error injectable event is on function entry

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Message-Id: <151394272357.5598.4199197920812849350.stgit@devbox>
Date:   Fri, 22 Dec 2017 20:38:43 +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 1/3] tracing/kprobe: bpf: Check error injectable event is on function entry

Check whether error injectable event is on function entry or not.
Currently it checks the event is ftrace-based kprobes or not,
but that is wrong. It should check if the event is on the entry
of target function. Since error injection will override a function
to just return with modified return value, that operation must
be done before the target function starts making stackframe.

As a side effect, bpf error injection is no need to depend on
function-tracer. It can work with sw-breakpoint based kprobe
events too.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/Kconfig        |    2 --
 kernel/trace/bpf_trace.c    |    6 +++---
 kernel/trace/trace_kprobe.c |    8 +++++---
 kernel/trace/trace_probe.h  |   12 ++++++------
 4 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index ae3a2d519e50..6400e1bf97c5 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -533,9 +533,7 @@ config FUNCTION_PROFILER
 config BPF_KPROBE_OVERRIDE
 	bool "Enable BPF programs to override a kprobed function"
 	depends on BPF_EVENTS
-	depends on KPROBES_ON_FTRACE
 	depends on HAVE_KPROBE_OVERRIDE
-	depends on DYNAMIC_FTRACE_WITH_REGS
 	default n
 	help
 	 Allows BPF to override the execution of a probed function and
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f6d2327ecb59..d663660f8392 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -800,11 +800,11 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
 	int ret = -EEXIST;
 
 	/*
-	 * Kprobe override only works for ftrace based kprobes, and only if they
-	 * are on the opt-in list.
+	 * Kprobe override only works if they are on the function entry,
+	 * and only if they are on the opt-in list.
 	 */
 	if (prog->kprobe_override &&
-	    (!trace_kprobe_ftrace(event->tp_event) ||
+	    (!trace_kprobe_on_func_entry(event->tp_event) ||
 	     !trace_kprobe_error_injectable(event->tp_event)))
 		return -EINVAL;
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 91f4b57dab82..265e3e27e8dc 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -88,13 +88,15 @@ static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
 	return nhit;
 }
 
-int trace_kprobe_ftrace(struct trace_event_call *call)
+bool trace_kprobe_on_func_entry(struct trace_event_call *call)
 {
 	struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
-	return kprobe_ftrace(&tk->rp.kp);
+
+	return kprobe_on_func_entry(tk->rp.kp.addr, tk->rp.kp.symbol_name,
+				    tk->rp.kp.offset);
 }
 
-int trace_kprobe_error_injectable(struct trace_event_call *call)
+bool trace_kprobe_error_injectable(struct trace_event_call *call)
 {
 	struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
 	unsigned long addr;
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 5e54d748c84c..e101c5bb9eda 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -252,8 +252,8 @@ struct symbol_cache;
 unsigned long update_symbol_cache(struct symbol_cache *sc);
 void free_symbol_cache(struct symbol_cache *sc);
 struct symbol_cache *alloc_symbol_cache(const char *sym, long offset);
-int trace_kprobe_ftrace(struct trace_event_call *call);
-int trace_kprobe_error_injectable(struct trace_event_call *call);
+bool trace_kprobe_on_func_entry(struct trace_event_call *call);
+bool trace_kprobe_error_injectable(struct trace_event_call *call);
 #else
 /* uprobes do not support symbol fetch methods */
 #define fetch_symbol_u8			NULL
@@ -280,14 +280,14 @@ alloc_symbol_cache(const char *sym, long offset)
 	return NULL;
 }
 
-static inline int trace_kprobe_ftrace(struct trace_event_call *call)
+static inline bool trace_kprobe_on_func_entry(struct trace_event_call *call)
 {
-	return 0;
+	return false;
 }
 
-static inline int trace_kprobe_error_injectable(struct trace_event_call *call)
+static inline bool trace_kprobe_error_injectable(struct trace_event_call *call)
 {
-	return 0;
+	return false;
 }
 #endif /* CONFIG_KPROBE_EVENTS */