From: Alexei Starovoitov ast@kernel.org
[ 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@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Steven Rostedt (VMware) rostedt@goodmis.org Link: https://lore.kernel.org/bpf/20210316195815.34714-1-alexei.starovoitov@gmail.... Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/ftrace.c | 43 ++++++++++++++++++++++++++++++++++++++----- 1 file changed, 38 insertions(+), 5 deletions(-)
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);