Patch "ftrace: Fix modify_ftrace_direct." has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ftrace: Fix modify_ftrace_direct.

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ftrace-fix-modify_ftrace_direct.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 288bf263ef53273c12853c0d4c54a6ffefda1b54
Author: Alexei Starovoitov <ast@xxxxxxxxxx>
Date:   Tue Mar 16 12:58:15 2021 -0700

    ftrace: Fix modify_ftrace_direct.
    
    [ Upstream commit 8a141dd7f7060d1e64c14a5257e0babae20ac99b ]
    
    The following sequence of commands:
      register_ftrace_direct(ip, addr1);
      modify_ftrace_direct(ip, addr1, addr2);
      unregister_ftrace_direct(ip, addr2);
    will cause the kernel to warn:
    [   30.179191] WARNING: CPU: 2 PID: 1961 at kernel/trace/ftrace.c:5223 unregister_ftrace_direct+0x130/0x150
    [   30.180556] CPU: 2 PID: 1961 Comm: test_progs    W  O      5.12.0-rc2-00378-g86bc10a0a711-dirty #3246
    [   30.182453] RIP: 0010:unregister_ftrace_direct+0x130/0x150
    
    When modify_ftrace_direct() changes the addr from old to new it should update
    the addr stored in ftrace_direct_funcs. Otherwise the final
    unregister_ftrace_direct() won't find the address and will cause the splat.
    
    Fixes: 0567d6809182 ("ftrace: Add modify_ftrace_direct()")
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20210316195815.34714-1-alexei.starovoitov@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9c1bba8cc51b..82041bbf8fc2 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5045,6 +5045,20 @@ struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr)
 	return NULL;
 }
 
+static struct ftrace_direct_func *ftrace_alloc_direct_func(unsigned long addr)
+{
+	struct ftrace_direct_func *direct;
+
+	direct = kmalloc(sizeof(*direct), GFP_KERNEL);
+	if (!direct)
+		return NULL;
+	direct->addr = addr;
+	direct->count = 0;
+	list_add_rcu(&direct->next, &ftrace_direct_funcs);
+	ftrace_direct_func_count++;
+	return direct;
+}
+
 /**
  * register_ftrace_direct - Call a custom trampoline directly
  * @ip: The address of the nop at the beginning of a function
@@ -5120,15 +5134,11 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 
 	direct = ftrace_find_direct_func(addr);
 	if (!direct) {
-		direct = kmalloc(sizeof(*direct), GFP_KERNEL);
+		direct = ftrace_alloc_direct_func(addr);
 		if (!direct) {
 			kfree(entry);
 			goto out_unlock;
 		}
-		direct->addr = addr;
-		direct->count = 0;
-		list_add_rcu(&direct->next, &ftrace_direct_funcs);
-		ftrace_direct_func_count++;
 	}
 
 	entry->ip = ip;
@@ -5329,6 +5339,7 @@ int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
 int modify_ftrace_direct(unsigned long ip,
 			 unsigned long old_addr, unsigned long new_addr)
 {
+	struct ftrace_direct_func *direct, *new_direct = NULL;
 	struct ftrace_func_entry *entry;
 	struct dyn_ftrace *rec;
 	int ret = -ENODEV;
@@ -5344,6 +5355,20 @@ int modify_ftrace_direct(unsigned long ip,
 	if (entry->direct != old_addr)
 		goto out_unlock;
 
+	direct = ftrace_find_direct_func(old_addr);
+	if (WARN_ON(!direct))
+		goto out_unlock;
+	if (direct->count > 1) {
+		ret = -ENOMEM;
+		new_direct = ftrace_alloc_direct_func(new_addr);
+		if (!new_direct)
+			goto out_unlock;
+		direct->count--;
+		new_direct->count++;
+	} else {
+		direct->addr = new_addr;
+	}
+
 	/*
 	 * If there's no other ftrace callback on the rec->ip location,
 	 * then it can be changed directly by the architecture.
@@ -5357,6 +5382,14 @@ int modify_ftrace_direct(unsigned long ip,
 		ret = 0;
 	}
 
+	if (unlikely(ret && new_direct)) {
+		direct->count++;
+		list_del_rcu(&new_direct->next);
+		synchronize_rcu_tasks();
+		kfree(new_direct);
+		ftrace_direct_func_count--;
+	}
+
  out_unlock:
 	mutex_unlock(&ftrace_lock);
 	mutex_unlock(&direct_mutex);