Subject: [PATCH 05/13] kprobe: Allow to get traced function address for multi ftrace kprobes

From: Jiri Olsa <[email-masked]>
Date: Tue, 4 Jan 2022 09:09:35 +0100

The current bpf_get_func_ip_kprobe helper does not work properly,
when used in ebpf program triggered by the new multi kprobes.

We can't use kprobe's func_addr in bpf_get_func_ip_kprobe helper,
because there are multiple functions registered for single kprobe
object.

Adding new per cpu variable current_ftrace_multi_addr and extra
address in kretprobe_instance object to keep current traced function
address for each cpu for both kprobe handler and kretprobe trampoline.

The address value is set/passed as follows, for kprobe:

  kprobe_ftrace_multi_handler
  {
    old = kprobe_ftrace_multi_addr_set(ip);
    handler..
    kprobe_ftrace_multi_addr_set(old);
  }

For kretprobe:

  kprobe_ftrace_multi_handler
  {
    old = kprobe_ftrace_multi_addr_set(ip);
    ...
      pre_handler_kretprobe
      {
        ri->ftrace_multi_addr = kprobe_ftrace_multi_addr
      }
    ...
    kprobe_ftrace_multi_addr_set(old);
  }

  __kretprobe_trampoline_handler
  {
    prev_func_addr = kprobe_ftrace_multi_addr_set(ri->ftrace_multi_addr);
    handler..
    kprobe_ftrace_multi_addr_set(prev_func_addr);
  }

Signed-off-by: Jiri Olsa <[email-masked]>
---
 arch/x86/kernel/kprobes/ftrace.c |  3 +++
 include/linux/kprobes.h          | 26 ++++++++++++++++++++++++++
 kernel/kprobes.c                 |  6 ++++++
 kernel/trace/bpf_trace.c         |  7 ++++++-
 4 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index ac4d256b89c6..8caaa58c3a64 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -72,6 +72,7 @@ NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 void kprobe_ftrace_multi_handler(unsigned long ip, unsigned long parent_ip,
 				 struct ftrace_ops *ops, struct ftrace_regs *fregs)
 {
+	unsigned long old;
 	struct kprobe *p;
 	int bit;
 
@@ -79,8 +80,10 @@ void kprobe_ftrace_multi_handler(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;
 
+	old = kprobe_ftrace_multi_addr_set(ip);
 	p = container_of(ops, struct kprobe, multi.ops);
 	ftrace_handler(p, ip, fregs);
+	kprobe_ftrace_multi_addr_set(old);
 
 	ftrace_test_recursion_unlock(bit);
 }
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index a31da6202b5c..3f0522b9538b 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -191,6 +191,7 @@ struct kretprobe_instance {
 	struct kretprobe_holder *rph;
 	kprobe_opcode_t *ret_addr;
 	void *fp;
+	unsigned long ftrace_multi_addr;
 	char data[];
 };
 
@@ -387,16 +388,37 @@ static inline void wait_for_kprobe_optimizer(void) { }
 #endif /* CONFIG_OPTPROBES */
 
 #ifdef CONFIG_KPROBES_ON_FTRACE
+DECLARE_PER_CPU(unsigned long, current_ftrace_multi_addr);
 extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 				  struct ftrace_ops *ops, struct ftrace_regs *fregs);
 extern void kprobe_ftrace_multi_handler(unsigned long ip, unsigned long parent_ip,
 					struct ftrace_ops *ops, struct ftrace_regs *fregs);
 extern int arch_prepare_kprobe_ftrace(struct kprobe *p);
+
+static inline unsigned long kprobe_ftrace_multi_addr(void)
+{
+	return __this_cpu_read(current_ftrace_multi_addr);
+}
+static inline unsigned long kprobe_ftrace_multi_addr_set(unsigned long addr)
+{
+	unsigned long old = __this_cpu_read(current_ftrace_multi_addr);
+
+	__this_cpu_write(current_ftrace_multi_addr, addr);
+	return old;
+}
 #else
 static inline int arch_prepare_kprobe_ftrace(struct kprobe *p)
 {
 	return -EINVAL;
 }
+static inline unsigned long kprobe_ftrace_multi_addr_set(unsigned long addr)
+{
+	return 0;
+}
+static inline unsigned long kprobe_ftrace_multi_addr(void)
+{
+	return 0;
+}
 #endif /* CONFIG_KPROBES_ON_FTRACE */
 
 /* Get the kprobe at this addr (if any) - called with preemption disabled */
@@ -514,6 +536,10 @@ static inline int kprobe_get_kallsym(unsigned int symnum, unsigned long *value,
 {
 	return -ERANGE;
 }
+static inline unsigned long kprobe_ftrace_multi_addr(void)
+{
+	return 0;
+}
 #endif /* CONFIG_KPROBES */
 
 static inline int disable_kretprobe(struct kretprobe *rp)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 04fc411ca30c..6ba249f3a0cb 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1064,6 +1064,8 @@ static bool in_kretprobe_blacklist(void *addr)
 }
 
 #ifdef CONFIG_KPROBES_ON_FTRACE
+DEFINE_PER_CPU(unsigned long, current_ftrace_multi_addr);
+
 static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
 	.func = kprobe_ftrace_handler,
 	.flags = FTRACE_OPS_FL_SAVE_REGS,
@@ -2106,11 +2108,14 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
 		rp = get_kretprobe(ri);
 		if (rp && rp->handler) {
 			struct kprobe *prev = kprobe_running();
+			unsigned long prev_func_addr;
 
+			prev_func_addr = kprobe_ftrace_multi_addr_set(ri->ftrace_multi_addr);
 			__this_cpu_write(current_kprobe, &rp->kp);
 			ri->ret_addr = correct_ret_addr;
 			rp->handler(ri, regs);
 			__this_cpu_write(current_kprobe, prev);
+			kprobe_ftrace_multi_addr_set(prev_func_addr);
 		}
 		if (first == node)
 			break;
@@ -2161,6 +2166,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 	}
 
 	arch_prepare_kretprobe(ri, regs);
+	ri->ftrace_multi_addr = kprobe_ftrace_multi_addr();
 
 	__llist_add(&ri->llist, &current->kretprobe_instances);
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 25631253084a..39f4d476cfca 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1026,7 +1026,12 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
 {
 	struct kprobe *kp = kprobe_running();
 
-	return kp ? (uintptr_t)kp->func_addr : 0;
+	if (!kp)
+		return 0;
+	if (kprobe_ftrace_multi(kp))
+		return (uintptr_t) kprobe_ftrace_multi_addr();
+	else
+		return (uintptr_t) kp->func_addr;
 }
 
 static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
-- 
2.33.1