Commit 8e5bad7d authored by Kees Cook's avatar Kees Cook Committed by Peter Zijlstra
Browse files

sched: Introduce struct balance_callback to avoid CFI mismatches 



Introduce distinct struct balance_callback instead of performing function
pointer casting which will trip CFI. Avoids warnings as found by Clang's
future -Wcast-function-type-strict option:

In file included from kernel/sched/core.c:84:
kernel/sched/sched.h:1755:15: warning: cast from 'void (*)(struct rq *)' to 'void (*)(struct callback_head *)' converts to incompatible function type [-Wcast-function-type-strict]
        head->func = (void (*)(struct callback_head *))func;
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

No binary differences result from this change.

This patch is a cleanup based on Brad Spengler/PaX Team's modifications
to sched code in their last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code
are mine and don't reflect the original grsecurity/PaX code.

Reported-by: default avatarSami Tolvanen <samitolvanen@google.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarNathan Chancellor <nathan@kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/1724
Link: https://lkml.kernel.org/r/20221008000758.2957718-1-keescook@chromium.org
parent e705968d

kernel/sched/core.c

+12 −12
Original line number Diff line number Diff line
@@ -4823,10 +4823,10 @@ static inline void finish_task(struct task_struct *prev) 


#ifdef CONFIG_SMP



static void do_balance_callbacks(struct rq *rq, struct callback_head *head)

static void do_balance_callbacks(struct rq *rq, struct balance_callback *head)

{

	void (*func)(struct rq *rq);

	struct callback_head *next;

	struct balance_callback *next;



	lockdep_assert_rq_held(rq);
@@ -4853,15 +4853,15 @@ static void balance_push(struct rq *rq); 
 * This abuse is tolerated because it places all the unlikely/odd cases behind

 * a single test, namely: rq->balance_callback == NULL.

 */

struct callback_head balance_push_callback = {

struct balance_callback balance_push_callback = {

	.next = NULL,

	.func = (void (*)(struct callback_head *))balance_push,

	.func = balance_push,

};



static inline struct callback_head *

static inline struct balance_callback *

__splice_balance_callbacks(struct rq *rq, bool split)

{

	struct callback_head *head = rq->balance_callback;

	struct balance_callback *head = rq->balance_callback;



	if (likely(!head))

		return NULL;
@@ -4883,7 +4883,7 @@ __splice_balance_callbacks(struct rq *rq, bool split) 
	return head;

}



static inline struct callback_head *splice_balance_callbacks(struct rq *rq)

static inline struct balance_callback *splice_balance_callbacks(struct rq *rq)

{

	return __splice_balance_callbacks(rq, true);

}
@@ -4893,7 +4893,7 @@ static void __balance_callbacks(struct rq *rq) 
	do_balance_callbacks(rq, __splice_balance_callbacks(rq, false));

}



static inline void balance_callbacks(struct rq *rq, struct callback_head *head)

static inline void balance_callbacks(struct rq *rq, struct balance_callback *head)

{

	unsigned long flags;
@@ -4910,12 +4910,12 @@ static inline void __balance_callbacks(struct rq *rq) 
{

}



static inline struct callback_head *splice_balance_callbacks(struct rq *rq)

static inline struct balance_callback *splice_balance_callbacks(struct rq *rq)

{

	return NULL;

}



static inline void balance_callbacks(struct rq *rq, struct callback_head *head)

static inline void balance_callbacks(struct rq *rq, struct balance_callback *head)

{

}
@@ -6188,7 +6188,7 @@ static void sched_core_balance(struct rq *rq) 
	preempt_enable();

}



static DEFINE_PER_CPU(struct callback_head, core_balance_head);

static DEFINE_PER_CPU(struct balance_callback, core_balance_head);



static void queue_core_balance(struct rq *rq)

{
@@ -7419,7 +7419,7 @@ static int __sched_setscheduler(struct task_struct *p, 
	int oldpolicy = -1, policy = attr->sched_policy;

	int retval, oldprio, newprio, queued, running;

	const struct sched_class *prev_class;

	struct callback_head *head;

	struct balance_callback *head;

	struct rq_flags rf;

	int reset_on_fork;

	int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;

kernel/sched/deadline.c

+2 −2
Original line number Diff line number Diff line
@@ -644,8 +644,8 @@ static inline bool need_pull_dl_task(struct rq *rq, struct task_struct *prev) 
	return rq->online && dl_task(prev);

}



static DEFINE_PER_CPU(struct callback_head, dl_push_head);

static DEFINE_PER_CPU(struct callback_head, dl_pull_head);

static DEFINE_PER_CPU(struct balance_callback, dl_push_head);

static DEFINE_PER_CPU(struct balance_callback, dl_pull_head);



static void push_dl_tasks(struct rq *);

static void pull_dl_task(struct rq *);

kernel/sched/rt.c

+2 −2
Original line number Diff line number Diff line
@@ -410,8 +410,8 @@ static inline int has_pushable_tasks(struct rq *rq) 
	return !plist_head_empty(&rq->rt.pushable_tasks);

}



static DEFINE_PER_CPU(struct callback_head, rt_push_head);

static DEFINE_PER_CPU(struct callback_head, rt_pull_head);

static DEFINE_PER_CPU(struct balance_callback, rt_push_head);

static DEFINE_PER_CPU(struct balance_callback, rt_pull_head);



static void push_rt_tasks(struct rq *);

static void pull_rt_task(struct rq *);

kernel/sched/sched.h

+10 −4
Original line number Diff line number Diff line
@@ -938,6 +938,12 @@ struct uclamp_rq { 
DECLARE_STATIC_KEY_FALSE(sched_uclamp_used);

#endif /* CONFIG_UCLAMP_TASK */



struct rq;

struct balance_callback {

	struct balance_callback *next;

	void (*func)(struct rq *rq);

};



/*

 * This is the main, per-CPU runqueue data structure.

 *
@@ -1036,7 +1042,7 @@ struct rq { 
	unsigned long		cpu_capacity;

	unsigned long		cpu_capacity_orig;



	struct callback_head	*balance_callback;

	struct balance_callback *balance_callback;



	unsigned char		nohz_idle_balance;

	unsigned char		idle_balance;
@@ -1544,7 +1550,7 @@ struct rq_flags { 
#endif

};



extern struct callback_head balance_push_callback;

extern struct balance_callback balance_push_callback;



/*

 * Lockdep annotation that avoids accidental unlocks; it's like a
@@ -1724,7 +1730,7 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p) 


static inline void

queue_balance_callback(struct rq *rq,

		       struct callback_head *head,

		       struct balance_callback *head,

		       void (*func)(struct rq *rq))

{

	lockdep_assert_rq_held(rq);
@@ -1737,7 +1743,7 @@ queue_balance_callback(struct rq *rq, 
	if (unlikely(head->next || rq->balance_callback == &balance_push_callback))

		return;



	head->func = (void (*)(struct callback_head *))func;

	head->func = func;

	head->next = rq->balance_callback;

	rq->balance_callback = head;

}