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@kernel.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/include/asm/kprobes.h

@@ -67,9 +67,7 @@ extern const int kretprobe_blacklist_size;
 void arch_remove_kprobe(struct kprobe *p);
 asmlinkage void kretprobe_trampoline(void);
 
-#ifdef CONFIG_KPROBES_ON_FTRACE
-extern void arch_ftrace_kprobe_override_function(struct pt_regs *regs);
-#endif
+extern void arch_kprobe_override_function(struct pt_regs *regs);
 
 /* Architecture specific copy of original instruction*/
 struct arch_specific_insn {

arch/x86/kernel/kprobes/core.c

@@ -1183,3 +1183,17 @@ int arch_trampoline_kprobe(struct kprobe *p)
 {
 	return 0;
 }
+
+asmlinkage void override_func(void);
+asm(
+	".type override_func, @function\n"
+	"override_func:\n"
+	"	ret\n"
+	".size override_func, .-override_func\n"
+);
+
+void arch_kprobe_override_function(struct pt_regs *regs)
+{
+	regs->ip = (unsigned long)&override_func;
+}
+NOKPROBE_SYMBOL(arch_kprobe_override_function);

arch/x86/kernel/kprobes/ftrace.c

@@ -97,17 +97,3 @@ int arch_prepare_kprobe_ftrace(struct kprobe *p)
 	p->ainsn.boostable = false;
 	return 0;
 }
-
-asmlinkage void override_func(void);
-asm(
-	".type override_func, @function\n"
-	"override_func:\n"
-	"	ret\n"
-	".size override_func, .-override_func\n"
-);
-
-void arch_ftrace_kprobe_override_function(struct pt_regs *regs)
-{
-	regs->ip = (unsigned long)&override_func;
-}
-NOKPROBE_SYMBOL(arch_ftrace_kprobe_override_function);

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

kernel/trace/bpf_trace.c

@@ -85,7 +85,7 @@ 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);
+	arch_kprobe_override_function(regs);
 	return 0;
 }
 
@@ -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;
 

kernel/trace/trace_kprobe.c

@@ -88,13 +88,16 @@ 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.addr ? NULL : tk->rp.kp.symbol_name,
+			tk->rp.kp.addr ? 0 : 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;

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 */