On Thu, Mar 25, 2021 at 10:26:32PM +0100, Daniel Borkmann wrote:

On 3/24/21 6:40 PM, Jiri Olsa wrote:

quoted

Currently module can be unloaded even if there's a trampoline
register in it. It's easily reproduced by running in parallel:

   # while :; do ./test_progs -t module_attach; done
   # while :; do rmmod bpf_testmod; sleep 0.5; done

Taking the module reference in case the trampoline's ip is
within the module code. Releasing it when the trampoline's
ip is unregistered.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
v2 changes:
   - fixed ip_module_put to do preempt_disable/preempt_enable

  kernel/bpf/trampoline.c | 31 +++++++++++++++++++++++++++++++
  1 file changed, 31 insertions(+)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 1f3a4be4b175..39e4280f94e4 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c

@@ -87,6 +87,26 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
  	return tr;
  }
+static struct module *ip_module_get(unsigned long ip)
+{
+	struct module *mod;
+	int err = 0;
+
+	preempt_disable();
+	mod = __module_text_address(ip);
+	if (mod && !try_module_get(mod))
+		err = -ENOENT;
+	preempt_enable();
+	return err ? ERR_PTR(err) : mod;
+}
+
+static void ip_module_put(unsigned long ip)
+{
+	preempt_disable();
+	module_put(__module_text_address(ip));
+	preempt_enable();

Could we cache the mod pointer in tr instead of doing another addr search
for dropping the ref?

right.. I moved it from the ftrace layer where this was not an option,
so I did not realize bpf_trampoline could get extended, will send new
version

thanks,
jirka

quoted

+}
+
  static int is_ftrace_location(void *ip)
  {
  	long addr;

@@ -108,6 +128,9 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
  		ret = unregister_ftrace_direct((long)ip, (long)old_addr);
  	else
  		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
+
+	if (!ret)
+		ip_module_put((unsigned long) ip);
  	return ret;
  }

@@ -126,6 +149,7 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad
  /* first time registering */
  static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
  {
+	struct module *mod;
  	void *ip = tr->func.addr;
  	int ret;

@@ -134,10 +158,17 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
  		return ret;
  	tr->func.ftrace_managed = ret;
+	mod = ip_module_get((unsigned long) ip);
+	if (IS_ERR(mod))
+		return -ENOENT;
+
  	if (tr->func.ftrace_managed)
  		ret = register_ftrace_direct((long)ip, (long)new_addr);
  	else
  		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
+
+	if (ret)
+		module_put(mod);
  	return ret;
  }