On Fri, Jun 05, 2020 at 10:38:55AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 05, 2020 at 11:52:13AM +1000, Stephen Rothwell wrote:
> > Commit
> >
> > a148866489fb ("sched: Replace rq::wake_list")
> >
> > added
> >
> > BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) !=
> > offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist));
> >
> > in kernel/smp.c. This seems to be failing - at least for gcc-8 (I
> > haven't seen any failures in my linux-next testing).
>
> CONFIG_GCC_PLUGIN_RANDSTRUCT=y
(FWIW, the plugins will only be enabled if the gcc plugins-dev package is
installed)
> working on it.
Either of these solutions should fix it. I'm not sure which is
preferred.
Collect them into a separate anonymous struct to keep them together
under randomization:
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 613bf7a21ae2..0f90239501c8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -654,8 +654,11 @@ struct task_struct {
unsigned int ptrace;
#ifdef CONFIG_SMP
- struct llist_node wake_entry;
- unsigned int wake_entry_type;
+ /* Keep these members together under __randomize_struct. */
+ struct {
+ struct llist_node wake_entry;
+ unsigned int wake_entry_type;
+ };
int on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* Current CPU: */
or just explicitly move them out of the randomized section:
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 613bf7a21ae2..f97b41ce1b13 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -641,6 +641,10 @@ struct task_struct {
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;
+#ifdef CONFIG_SMP
+ struct llist_node wake_entry;
+ unsigned int wake_entry_type;
+#endif
/*
* This begins the randomizable portion of task_struct. Only
* scheduling-critical items should be added above here.
@@ -654,8 +658,6 @@ struct task_struct {
unsigned int ptrace;
#ifdef CONFIG_SMP
- struct llist_node wake_entry;
- unsigned int wake_entry_type;
int on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* Current CPU: */
--
Kees Cook
