Allows a binder node to specify whether it wants to
inherit real-time scheduling policy from a caller. This
inheritance may not always be desirable, for example in
cases where the binder call runs untrusted and therefore
potentially unbounded code.
Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
---
drivers/android/binder.c | 21 +++++++++++++++------
include/uapi/linux/android/binder.h | 8 ++++++++
2 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 4c42e268b1a5..5958a0876fe8 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -358,6 +358,8 @@ struct binder_error {
* (invariant after initialized)
* @min_priority: minimum scheduling priority
* (invariant after initialized)
+ * @inherit_rt: inherit RT scheduling policy from caller
+ * (invariant after initialized)
* @async_todo: list of async work items
* (protected by @proc->inner_lock)
*
@@ -394,6 +396,7 @@ struct binder_node {
* invariant after initialization
*/
u8 sched_policy:2;
+ u8 inherit_rt:1;
u8 accept_fds:1;
u8 min_priority;
};
@@ -1214,9 +1217,10 @@ static void binder_set_priority(struct task_struct *task,
static void binder_transaction_priority(struct task_struct *task,
struct binder_transaction *t,
- struct binder_priority node_prio)
+ struct binder_priority node_prio,
+ bool inherit_rt)
{
- struct binder_priority desired_prio;
+ struct binder_priority desired_prio = t->priority;
if (t->set_priority_called)
return;
@@ -1225,8 +1229,10 @@ static void binder_transaction_priority(struct task_struct *task,
t->saved_priority.sched_policy = task->policy;
t->saved_priority.prio = task->normal_prio;
- desired_prio.prio = t->priority.prio;
- desired_prio.sched_policy = t->priority.sched_policy;
+ if (!inherit_rt && is_rt_policy(desired_prio.sched_policy)) {
+ desired_prio.prio = NICE_TO_PRIO(0);
+ desired_prio.sched_policy = SCHED_NORMAL;
+ }
if (node_prio.prio < t->priority.prio ||
(node_prio.prio == t->priority.prio &&
@@ -1332,6 +1338,7 @@ static struct binder_node *binder_init_node_ilocked(
FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT;
node->min_priority = to_kernel_prio(node->sched_policy, priority);
node->accept_fds = !!(flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
+ node->inherit_rt = !!(flags & FLAT_BINDER_FLAG_INHERIT_RT);
spin_lock_init(&node->lock);
INIT_LIST_HEAD(&node->work.entry);
INIT_LIST_HEAD(&node->async_todo);
@@ -2749,7 +2756,8 @@ static bool binder_proc_transaction(struct binder_transaction *t,
if (thread) {
target_list = &thread->todo;
- binder_transaction_priority(thread->task, t, node_prio);
+ binder_transaction_priority(thread->task, t, node_prio,
+ node->inherit_rt);
} else if (!target_list) {
target_list = &proc->todo;
} else {
@@ -4173,7 +4181,8 @@ static int binder_thread_read(struct binder_proc *proc,
tr.cookie = target_node->cookie;
node_prio.sched_policy = target_node->sched_policy;
node_prio.prio = target_node->min_priority;
- binder_transaction_priority(current, t, node_prio);
+ binder_transaction_priority(current, t, node_prio,
+ target_node->inherit_rt);
cmd = BR_TRANSACTION;
} else {
tr.target.ptr = 0;
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index b3bced80adea..5539933b3491 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -79,6 +79,14 @@ enum flat_binder_object_flags {
*/
FLAT_BINDER_FLAG_SCHED_POLICY_MASK =
3U << FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT,
+
+ /**
+ * @FLAT_BINDER_FLAG_INHERIT_RT: whether the node inherits RT policy
+ *
+ * Only when set, calls into this node will inherit a real-time
+ * scheduling policy from the caller (for synchronous transactions).
+ */
+ FLAT_BINDER_FLAG_INHERIT_RT = 0x800,
};
#ifdef BINDER_IPC_32BIT
--
2.15.0.rc2.357.g7e34df9404-goog
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