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Date: Thu, 13 Oct 2022 13:00:00 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] sched: Introduce struct balance_callback to avoid CFI
mismatches
On Fri, Oct 07, 2022 at 05:07:58PM -0700, Kees Cook wrote:
> 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: Sami Tolvanen <samitolvanen@...gle.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1724
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> ---
> kernel/sched/core.c | 24 ++++++++++++------------
> kernel/sched/deadline.c | 4 ++--
> kernel/sched/rt.c | 4 ++--
> kernel/sched/sched.h | 14 ++++++++++----
> 4 files changed, 26 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ee28253c9ac0..911db628092e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4815,10 +4815,10 @@ 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);
>
> @@ -4845,15 +4845,15 @@ 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;
> @@ -4875,7 +4875,7 @@ __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);
> }
> @@ -4885,7 +4885,7 @@ 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;
>
> @@ -4902,12 +4902,12 @@ 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)
> {
> }
>
> @@ -6179,7 +6179,7 @@ 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)
> {
> @@ -7410,7 +7410,7 @@ 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;
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0ab79d819a0d..6498951b7d41 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -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 *);
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 55f39c8f4203..ad020a2a72f3 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -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 *);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index e26688d387ae..54971a57a4ea 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -953,6 +953,12 @@ 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.
> *
> @@ -1051,7 +1057,7 @@ 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;
> @@ -1559,7 +1565,7 @@ 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
> @@ -1739,7 +1745,7 @@ 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);
> @@ -1752,7 +1758,7 @@ 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;
> }
> --
> 2.34.1
>
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