binder: make FIFO inheritance a per-context option

Add a new ioctl to binder to control whether FIFO inheritance should happen.
In particular, hwbinder should inherit FIFO priority from callers, but standard
binder threads should not.

Test: boots

bug 36516194

Signed-off-by: Tim Murray <timmurray@google.com>
Change-Id: I8100c4364b7d15d1bf00a8ca5c286e4d4b23ce85

1 files changed, 36 insertions, 1 deletions

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index a078fcc22..06555e841 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -271,6 +271,7 @@ struct binder_context {
 
 	kuid_t binder_context_mgr_uid;
 	const char *name;
+	bool inherit_fifo_prio;
 };
 
 struct binder_device {
@@ -1186,6 +1187,7 @@ static void binder_transaction_priority(struct task_struct *task,
 					struct binder_priority node_prio,
 					bool inherit_rt)
 {
+	bool inherit_fifo = t->buffer->target_node->proc->context->inherit_fifo_prio;
 	struct binder_priority desired_prio;
 
 	if (t->set_priority_called)
@@ -1195,7 +1197,7 @@ static void binder_transaction_priority(struct task_struct *task,
 	t->saved_priority.sched_policy = task->policy;
 	t->saved_priority.prio = task->normal_prio;
 
-	if (!inherit_rt && is_rt_policy(desired_prio.sched_policy)) {
+	if (!inherit_rt && is_rt_policy(desired_prio.sched_policy) && !inherit_fifo) {
 		desired_prio.prio = NICE_TO_PRIO(0);
 		desired_prio.sched_policy = SCHED_NORMAL;
 	} else {
@@ -4499,6 +4501,33 @@ out:
 	return ret;
 }
 
+static int binder_ioctl_set_inherit_fifo_prio(struct file *filp)
+{
+	int ret = 0;
+	struct binder_proc *proc = filp->private_data;
+	struct binder_context *context = proc->context;
+
+	kuid_t curr_euid = current_euid();
+	mutex_lock(&context->context_mgr_node_lock);
+
+	if (uid_valid(context->binder_context_mgr_uid)) {
+		if (!uid_eq(context->binder_context_mgr_uid, curr_euid)) {
+			pr_err("BINDER_SET_INHERIT_FIFO_PRIO bad uid %d != %d\n",
+			       from_kuid(&init_user_ns, curr_euid),
+			       from_kuid(&init_user_ns,
+					 context->binder_context_mgr_uid));
+			ret = -EPERM;
+			goto out;
+		}
+	}
+
+	context->inherit_fifo_prio = true;
+
+ out:
+	mutex_unlock(&context->context_mgr_node_lock);
+	return ret;
+}
+
 static int binder_ioctl_set_ctx_mgr(struct file *filp)
 {
 	int ret = 0;
@@ -4617,6 +4646,11 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		if (ret)
 			goto err;
 		break;
+	case BINDER_SET_INHERIT_FIFO_PRIO:
+		ret = binder_ioctl_set_inherit_fifo_prio(filp);
+		if (ret)
+			goto err;
+		break;
 	case BINDER_THREAD_EXIT:
 		binder_debug(BINDER_DEBUG_THREADS, "%d:%d exit\n",
 			     proc->pid, thread->pid);
@@ -5388,6 +5422,7 @@ static void print_binder_proc_stats(struct seq_file *m,
 
 	seq_printf(m, "proc %d\n", proc->pid);
 	seq_printf(m, "context %s\n", proc->context->name);
+	seq_printf(m, "context FIFO: %d\n", proc->context->inherit_fifo_prio);
 	count = 0;
 	ready_threads = 0;
 	binder_inner_proc_lock(proc);