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

Jiri Olsa
2022-01-04T08:10:25Z

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 <jolsa@kernel.org>
---
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