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Date: Thu, 15 Feb 2024 16:23:55 +0100
From: Benjamin Tissoires <bentiss@kernel.org>
To: Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, John Fastabend <john.fastabend@gmail.com>, 
	Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, 
	Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Jiri Kosina <jikos@kernel.org>, Benjamin Tissoires <benjamin.tissoires@redhat.com>, 
	Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-input@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH RFC bpf-next v2 02/10] bpf/helpers: introduce sleepable
 timers
Message-ID: <mth43jfjhwtatwfo3unefrze62opht3yklleblslyz2adc6p5p@wm3miaqhhtkt>
References: <20240214-hid-bpf-sleepable-v2-0-5756b054724d@kernel.org>
 <20240214-hid-bpf-sleepable-v2-2-5756b054724d@kernel.org>
Precedence: bulk
MIME-Version: 1.0
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In-Reply-To: <20240214-hid-bpf-sleepable-v2-2-5756b054724d@kernel.org>

On Feb 14 2024, Benjamin Tissoires wrote:
> They are implemented as a kfunc, which means a little bit of tweaks in
> the verifier.
> 
> Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
> 
> ---
> 
> changes in v2 (compared to the one attaches to v1 0/9):
> - make use of a kfunc
> - add a (non-used) BPF_F_TIMER_SLEEPABLE
> - the callback is *not* called, it makes the kernel crashes
> ---
>  include/linux/bpf_verifier.h |   2 +
>  include/uapi/linux/bpf.h     |  12 +++++
>  kernel/bpf/helpers.c         | 105 ++++++++++++++++++++++++++++++++++++++++---
>  kernel/bpf/verifier.c        |  72 ++++++++++++++++++++++++++---
>  4 files changed, 180 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 84365e6dd85d..789ef5fec547 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -426,6 +426,7 @@ struct bpf_verifier_state {
>  	 * while they are still in use.
>  	 */
>  	bool used_as_loop_entry;
> +	bool in_sleepable;
>  
>  	/* first and last insn idx of this verifier state */
>  	u32 first_insn_idx;
> @@ -626,6 +627,7 @@ struct bpf_subprog_info {
>  	bool is_async_cb: 1;
>  	bool is_exception_cb: 1;
>  	bool args_cached: 1;
> +	bool is_sleepable: 1;
>  
>  	u8 arg_cnt;
>  	struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS];
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d96708380e52..0838597028a9 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7427,6 +7427,18 @@ enum {
>  	BPF_F_TIMER_CPU_PIN = (1ULL << 1),
>  };
>  
> +/* Extra flags to control bpf_timer_init() behaviour, in addition to CLOCK_*.
> + *     - BPF_F_TIMER_SLEEPABLE: Timer will run in a workqueue in a sleepable
> + *       context.
> + */
> +enum {
> +	/* CLOCK_* are using bits 0 to 3 */
> +	BPF_F_TIMER_SLEEPABLE = (1ULL << 4),
> +	__MAX_BPF_F_TIMER_INIT,
> +};
> +
> +#define MAX_BPF_F_TIMER_INIT __MAX_BPF_F_TIMER_INIT
> +
>  /* BPF numbers iterator state */
>  struct bpf_iter_num {
>  	/* opaque iterator state; having __u64 here allows to preserve correct
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 4db1c658254c..2dbc09ce841a 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1097,9 +1097,11 @@ const struct bpf_func_proto bpf_snprintf_proto = {
>   */
>  struct bpf_hrtimer {
>  	struct hrtimer timer;
> +	struct work_struct work;
>  	struct bpf_map *map;
>  	struct bpf_prog *prog;
>  	void __rcu *callback_fn;
> +	void __rcu *sleepable_cb_fn;
>  	void *value;
>  };
>  
> @@ -1113,18 +1115,59 @@ struct bpf_timer_kern {
>  	struct bpf_spin_lock lock;
>  } __attribute__((aligned(8)));
>  
> +static void bpf_timer_work_cb(struct work_struct *work)
> +{
> +	struct bpf_hrtimer *t = container_of(work, struct bpf_hrtimer, work);
> +	struct bpf_map *map = t->map;
> +	void *value = t->value;
> +	bpf_callback_t callback_fn;
> +	void *key;
> +	u32 idx;
> +
> +	BTF_TYPE_EMIT(struct bpf_timer);
> +
> +	rcu_read_lock();
> +	callback_fn = rcu_dereference(t->sleepable_cb_fn);
> +	rcu_read_unlock();
> +	if (!callback_fn)
> +		return;
> +
> +	/* FIXME: do we need any locking? */
> +	if (map->map_type == BPF_MAP_TYPE_ARRAY) {
> +		struct bpf_array *array = container_of(map, struct bpf_array, map);
> +
> +		/* compute the key */
> +		idx = ((char *)value - array->value) / array->elem_size;
> +		key = &idx;
> +	} else { /* hash or lru */
> +		key = value - round_up(map->key_size, 8);
> +	}
> +
> +	/* FIXME: this crashes the system with
> +	 * BUG: kernel NULL pointer dereference, address: 000000000000000b
> +	 */
> +	/* callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0); */

I've found an interesting side effect here.

If I uncomment the line above, I get the following dumpstack:

[    5.375257] BUG: kernel NULL pointer dereference, address: 000000000000000b
[    5.376587] #PF: supervisor instruction fetch in kernel mode
[    5.376932] #PF: error_code(0x0010) - not-present page
[    5.377249] PGD 1016e6067 P4D 1016e6067 PUD 1016e5067 PMD 0 
[    5.377602] Oops: 0010 [#1] PREEMPT SMP NOPTI
[    5.377876] CPU: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.8.0-rc2-gd2c1e1837606-dirty #285
[    5.378378] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
[    5.378913] Workqueue: events bpf_timer_work_cb
[    5.379197] RIP: 0010:0xb
[    5.379369] Code: Unable to access opcode bytes at 0xffffffffffffffe1.
[    5.379768] RSP: 0018:ffffa5300005be10 EFLAGS: 00010246
[    5.380088] RAX: 0000000000000068 RBX: 000000000000000b RCX: 0000000000000000
[    5.380523] RDX: ffffa530012a5ff0 RSI: ffffa530012a5fe8 RDI: ffff915ec2bad000
[    5.380947] RBP: ffff915ec2bad000 R08: 0000000000000000 R09: 0000000000000001
[    5.381368] R10: 0000000000000000 R11: ffffffff9166f820 R12: ffffa530012a5ff0
[    5.381793] R13: ffffa530012a5fe8 R14: ffff915ec0073005 R15: ffffffff900aea8a
[    5.382213] FS:  0000000000000000(0000) GS:ffff915efbc00000(0000) knlGS:0000000000000000
[    5.382691] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    5.383036] CR2: ffffffffffffffe1 CR3: 000000010761e003 CR4: 0000000000770ef0
[    5.383460] PKRU: 55555554
[    5.383643] Call Trace:
[    5.383831]  <TASK>
[    5.383994]  ? __die+0x23/0x70
[    5.384228]  ? page_fault_oops+0x181/0x4a0
[    5.384541]  ? exc_page_fault+0x67/0x1a0
[    5.384840]  ? asm_exc_page_fault+0x26/0x30
[    5.385154]  ? process_one_work+0x16a/0x4b0
[    5.385467]  ? bpf_timer_work_cb+0xfc/0x240
[    5.385789]  ? process_one_work+0x1d4/0x4b0
[    5.386101]  ? worker_thread+0x1d5/0x3c0
[    5.386393]  ? __pfx_worker_thread+0x10/0x10
[    5.386724]  ? kthread+0xf5/0x130
[    5.386974]  ? __pfx_kthread+0x10/0x10
[    5.387255]  ? ret_from_fork+0x31/0x50
[    5.387537]  ? __pfx_kthread+0x10/0x10
[    5.387820]  ? ret_from_fork_asm+0x1b/0x30
[    5.388127]  </TASK>

And it looks like the callback is properly called, but the fault comes
after:

(gdb) list *(process_one_work+0x16a)
0xffffffff810aea8a is in process_one_work (kernel/workqueue.c:2606).
2601		 * disabled.
2602		 */
2603		set_work_pool_and_clear_pending(work, pool->id);
2604	
2605		pwq->stats[PWQ_STAT_STARTED]++;
2606		raw_spin_unlock_irq(&pool->lock);
2607	
2608		lock_map_acquire(&pwq->wq->lockdep_map);
2609		lock_map_acquire(&lockdep_map);
2610		/*

And there is no real reason for the spinlock to not be set unless there
is a memroy corruption.

And if in my program I call bpf_timer_set_callback() before bpf_timer_set_sleepable_cb()
like:
	bpf_timer_set_callback(timer, timer_cb1);
	bpf_timer_set_sleepable_cb(timer, timer_cb1);

I do not see the corruption in the memory.

So it seems that when BPF calls the helper, the callback_fn is set in a
mode that it is not polluting the memory, while when calling the function
pointer from a kfunc, something is not properly set and there is a
memory corruption.

Does that rings any bell?

> +	/* The verifier checked that return value is zero. */
> +}
> +
>  static DEFINE_PER_CPU(struct bpf_hrtimer *, hrtimer_running);
>  
>  static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
>  {
>  	struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer);
> +	bpf_callback_t callback_fn, sleepable_cb_fn;
>  	struct bpf_map *map = t->map;
>  	void *value = t->value;
> -	bpf_callback_t callback_fn;
>  	void *key;
>  	u32 idx;
>  
>  	BTF_TYPE_EMIT(struct bpf_timer);
> +	sleepable_cb_fn = rcu_dereference_check(t->sleepable_cb_fn, rcu_read_lock_bh_held());
> +	if (sleepable_cb_fn) {
> +		schedule_work(&t->work);
> +		goto out;
> +	}
> +
>  	callback_fn = rcu_dereference_check(t->callback_fn, rcu_read_lock_bh_held());
>  	if (!callback_fn)
>  		goto out;
> @@ -1154,10 +1197,14 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
>  	return HRTIMER_NORESTART;
>  }
>  
> +#define BPF_TIMER_CLOCK_MASK (MAX_CLOCKS - 1)  /* 0xf */
> +#define BPF_TIMER_FLAGS_MASK GENMASK_ULL(63, 4)
> +
>  BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map,
>  	   u64, flags)
>  {
> -	clockid_t clockid = flags & (MAX_CLOCKS - 1);
> +	clockid_t clockid = flags & BPF_TIMER_CLOCK_MASK;
> +	u64 bpf_timer_flags = flags & BPF_TIMER_FLAGS_MASK;
>  	struct bpf_hrtimer *t;
>  	int ret = 0;
>  
> @@ -1168,7 +1215,7 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map
>  	if (in_nmi())
>  		return -EOPNOTSUPP;
>  
> -	if (flags >= MAX_CLOCKS ||
> +	if (bpf_timer_flags & ~(BPF_F_TIMER_SLEEPABLE) ||
>  	    /* similar to timerfd except _ALARM variants are not supported */
>  	    (clockid != CLOCK_MONOTONIC &&
>  	     clockid != CLOCK_REALTIME &&
> @@ -1190,7 +1237,10 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map
>  	t->map = map;
>  	t->prog = NULL;
>  	rcu_assign_pointer(t->callback_fn, NULL);
> +	rcu_assign_pointer(t->sleepable_cb_fn, NULL);
> +	/* FIXME: probably do something about the SLEEPABLE flag */
>  	hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT);
> +	INIT_WORK(&t->work, bpf_timer_work_cb);
>  	t->timer.function = bpf_timer_cb;
>  	WRITE_ONCE(timer->timer, t);
>  	/* Guarantee the order between timer->timer and map->usercnt. So
> @@ -1221,8 +1271,8 @@ static const struct bpf_func_proto bpf_timer_init_proto = {
>  	.arg3_type	= ARG_ANYTHING,
>  };
>  
> -BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn,
> -	   struct bpf_prog_aux *, aux)
> +static int __bpf_timer_set_callback(struct bpf_timer_kern *timer, void *callback_fn,
> +				    struct bpf_prog_aux *aux, bool is_sleepable)
>  {
>  	struct bpf_prog *prev, *prog = aux->prog;
>  	struct bpf_hrtimer *t;
> @@ -1260,12 +1310,24 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb
>  			bpf_prog_put(prev);
>  		t->prog = prog;
>  	}
> -	rcu_assign_pointer(t->callback_fn, callback_fn);
> +	if (is_sleepable) {
> +		rcu_assign_pointer(t->sleepable_cb_fn, callback_fn);
> +		rcu_assign_pointer(t->callback_fn, NULL);
> +	} else {
> +		rcu_assign_pointer(t->callback_fn, callback_fn);
> +		rcu_assign_pointer(t->sleepable_cb_fn, NULL);
> +	}
>  out:
>  	__bpf_spin_unlock_irqrestore(&timer->lock);
>  	return ret;
>  }
>  
> +BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn,
> +	   struct bpf_prog_aux *, aux)
> +{
> +	return __bpf_timer_set_callback(timer, callback_fn, aux, false);
> +}
> +
>  static const struct bpf_func_proto bpf_timer_set_callback_proto = {
>  	.func		= bpf_timer_set_callback,
>  	.gpl_only	= true,
> @@ -1353,6 +1415,7 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_timer_kern *, timer)
>  	 * if it was running.
>  	 */
>  	ret = ret ?: hrtimer_cancel(&t->timer);
> +	ret = ret ?: cancel_work_sync(&t->work);
>  	return ret;
>  }
>  
> @@ -1407,6 +1470,8 @@ void bpf_timer_cancel_and_free(void *val)
>  	 */
>  	if (this_cpu_read(hrtimer_running) != t)
>  		hrtimer_cancel(&t->timer);
> +
> +	cancel_work_sync(&t->work);
>  	kfree(t);
>  }
>  
> @@ -2542,6 +2607,33 @@ __bpf_kfunc void bpf_throw(u64 cookie)
>  	WARN(1, "A call to BPF exception callback should never return\n");
>  }
>  
> +/* FIXME: use kernel doc style */
> +/* Description
> + *	Configure the timer to call *callback_fn* static function in a
> + *	sleepable context.
> + * Return
> + *	0 on success.
> + *	**-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier.
> + *	**-EPERM** if *timer* is in a map that doesn't have any user references.
> + *	The user space should either hold a file descriptor to a map with timers
> + *	or pin such map in bpffs. When map is unpinned or file descriptor is
> + *	closed all timers in the map will be cancelled and freed.
> + */
> +__bpf_kfunc int bpf_timer_set_sleepable_cb(struct bpf_timer_kern *timer,
> +					   int (callback_fn)(void *map, int *key, struct bpf_timer *timer))
> +{
> +	struct bpf_throw_ctx ctx = {};
> +
> +	/* FIXME: definietely not sure this is OK */
> +	arch_bpf_stack_walk(bpf_stack_walker, &ctx);
> +	WARN_ON_ONCE(!ctx.aux);
> +
> +	if (!ctx.aux)
> +		return -EINVAL;
> +
> +	return __bpf_timer_set_callback(timer, (void *)callback_fn, ctx.aux, true);
> +}
> +
>  __bpf_kfunc_end_defs();
>  
>  BTF_KFUNCS_START(generic_btf_ids)
> @@ -2573,6 +2665,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
>  #endif
>  BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
>  BTF_ID_FLAGS(func, bpf_throw)
> +BTF_ID_FLAGS(func, bpf_timer_set_sleepable_cb)

I also just realized that this should go into common_btf_ids so that
anybody can use it, not just tracing.

Cheers,
Benjamin

>  BTF_KFUNCS_END(generic_btf_ids)
>  
>  static const struct btf_kfunc_id_set generic_kfunc_set = {
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 7831adba9abf..67da3f7bddb5 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -503,6 +503,8 @@ static bool is_dynptr_ref_function(enum bpf_func_id func_id)
>  static bool is_sync_callback_calling_kfunc(u32 btf_id);
>  static bool is_bpf_throw_kfunc(struct bpf_insn *insn);
>  
> +static bool is_bpf_timer_set_sleepable_cb_kfunc(u32 btf_id);
> +
>  static bool is_sync_callback_calling_function(enum bpf_func_id func_id)
>  {
>  	return func_id == BPF_FUNC_for_each_map_elem ||
> @@ -513,7 +515,8 @@ static bool is_sync_callback_calling_function(enum bpf_func_id func_id)
>  
>  static bool is_async_callback_calling_function(enum bpf_func_id func_id)
>  {
> -	return func_id == BPF_FUNC_timer_set_callback;
> +	return func_id == BPF_FUNC_timer_set_callback ||
> +	       is_bpf_timer_set_sleepable_cb_kfunc(func_id);
>  }
>  
>  static bool is_callback_calling_function(enum bpf_func_id func_id)
> @@ -1414,6 +1417,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
>  	}
>  	dst_state->speculative = src->speculative;
>  	dst_state->active_rcu_lock = src->active_rcu_lock;
> +	dst_state->in_sleepable = src->in_sleepable;
>  	dst_state->curframe = src->curframe;
>  	dst_state->active_lock.ptr = src->active_lock.ptr;
>  	dst_state->active_lock.id = src->active_lock.id;
> @@ -2413,6 +2417,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env,
>  	 * Initialize it similar to do_check_common().
>  	 */
>  	elem->st.branches = 1;
> +	elem->st.in_sleepable = env->subprog_info[subprog].is_sleepable;
>  	frame = kzalloc(sizeof(*frame), GFP_KERNEL);
>  	if (!frame)
>  		goto err;
> @@ -5257,7 +5262,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
>  
>  static bool in_sleepable(struct bpf_verifier_env *env)
>  {
> -	return env->prog->aux->sleepable;
> +	return env->prog->aux->sleepable ||
> +	       (env->cur_state && env->cur_state->in_sleepable);
>  }
>  
>  /* The non-sleepable programs and sleepable programs with explicit bpf_rcu_read_lock()
> @@ -5439,6 +5445,26 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
>  					return -EACCES;
>  				}
>  				break;
> +			case BPF_TIMER:
> +				/* FIXME: kptr does the above, should we use the same? */
> +				if (src != ACCESS_DIRECT) {
> +					verbose(env, "bpf_timer cannot be accessed indirectly by helper\n");
> +					return -EACCES;
> +				}
> +				if (!tnum_is_const(reg->var_off)) {
> +					verbose(env, "bpf_timer access cannot have variable offset\n");
> +					return -EACCES;
> +				}
> +				if (p != off + reg->var_off.value) {
> +					verbose(env, "bpf_timer access misaligned expected=%u off=%llu\n",
> +						p, off + reg->var_off.value);
> +					return -EACCES;
> +				}
> +				if (size != bpf_size_to_bytes(BPF_DW)) {
> +					verbose(env, "bpf_timer access size must be BPF_DW\n");
> +					return -EACCES;
> +				}
> +				break;
>  			default:
>  				verbose(env, "%s cannot be accessed directly by load/store\n",
>  					btf_field_type_name(field->type));
> @@ -9439,11 +9465,13 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins
>  
>  	if (insn->code == (BPF_JMP | BPF_CALL) &&
>  	    insn->src_reg == 0 &&
> -	    insn->imm == BPF_FUNC_timer_set_callback) {
> +	    (insn->imm == BPF_FUNC_timer_set_callback ||
> +	     is_bpf_timer_set_sleepable_cb_kfunc(insn->imm))) {
>  		struct bpf_verifier_state *async_cb;
>  
>  		/* there is no real recursion here. timer callbacks are async */
>  		env->subprog_info[subprog].is_async_cb = true;
> +		env->subprog_info[subprog].is_sleepable = is_bpf_timer_set_sleepable_cb_kfunc(insn->imm);
>  		async_cb = push_async_cb(env, env->subprog_info[subprog].start,
>  					 insn_idx, subprog);
>  		if (!async_cb)
> @@ -10412,6 +10440,10 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>  		break;
>  	}
>  
> +	if (is_bpf_timer_set_sleepable_cb_kfunc(func_id))
> +		err = push_callback_call(env, insn, insn_idx, meta.subprogno,
> +					 set_timer_callback_state);
> +
>  	if (err)
>  		return err;
>  
> @@ -10789,6 +10821,7 @@ enum {
>  	KF_ARG_LIST_NODE_ID,
>  	KF_ARG_RB_ROOT_ID,
>  	KF_ARG_RB_NODE_ID,
> +	KF_ARG_TIMER_ID,
>  };
>  
>  BTF_ID_LIST(kf_arg_btf_ids)
> @@ -10797,6 +10830,7 @@ BTF_ID(struct, bpf_list_head)
>  BTF_ID(struct, bpf_list_node)
>  BTF_ID(struct, bpf_rb_root)
>  BTF_ID(struct, bpf_rb_node)
> +BTF_ID(struct, bpf_timer_kern)
>  
>  static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
>  				    const struct btf_param *arg, int type)
> @@ -10840,6 +10874,12 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par
>  	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID);
>  }
>  
> +static bool is_kfunc_arg_timer(const struct btf *btf, const struct btf_param *arg)
> +{
> +	bool ret = __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_TIMER_ID);
> +	return ret;
> +}
> +
>  static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
>  				  const struct btf_param *arg)
>  {
> @@ -10908,6 +10948,7 @@ enum kfunc_ptr_arg_type {
>  	KF_ARG_PTR_TO_RB_NODE,
>  	KF_ARG_PTR_TO_NULL,
>  	KF_ARG_PTR_TO_CONST_STR,
> +	KF_ARG_PTR_TO_TIMER,
>  };
>  
>  enum special_kfunc_type {
> @@ -10934,6 +10975,7 @@ enum special_kfunc_type {
>  	KF_bpf_percpu_obj_drop_impl,
>  	KF_bpf_throw,
>  	KF_bpf_iter_css_task_new,
> +	KF_bpf_timer_set_sleepable_cb,
>  };
>  
>  BTF_SET_START(special_kfunc_set)
> @@ -10960,6 +11002,7 @@ BTF_ID(func, bpf_throw)
>  #ifdef CONFIG_CGROUPS
>  BTF_ID(func, bpf_iter_css_task_new)
>  #endif
> +BTF_ID(func, bpf_timer_set_sleepable_cb)
>  BTF_SET_END(special_kfunc_set)
>  
>  BTF_ID_LIST(special_kfunc_list)
> @@ -10990,6 +11033,7 @@ BTF_ID(func, bpf_iter_css_task_new)
>  #else
>  BTF_ID_UNUSED
>  #endif
> +BTF_ID(func, bpf_timer_set_sleepable_cb)
>  
>  static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
>  {
> @@ -11061,6 +11105,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
>  	if (is_kfunc_arg_const_str(meta->btf, &args[argno]))
>  		return KF_ARG_PTR_TO_CONST_STR;
>  
> +	if (is_kfunc_arg_timer(meta->btf, &args[argno]))
> +		return KF_ARG_PTR_TO_TIMER;
> +
>  	if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
>  		if (!btf_type_is_struct(ref_t)) {
>  			verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
> @@ -11318,6 +11365,11 @@ static bool is_bpf_throw_kfunc(struct bpf_insn *insn)
>  	       insn->imm == special_kfunc_list[KF_bpf_throw];
>  }
>  
> +static bool is_bpf_timer_set_sleepable_cb_kfunc(u32 btf_id)
> +{
> +	return btf_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb];
> +}
> +
>  static bool is_rbtree_lock_required_kfunc(u32 btf_id)
>  {
>  	return is_bpf_rbtree_api_kfunc(btf_id);
> @@ -11693,6 +11745,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
>  		case KF_ARG_PTR_TO_CALLBACK:
>  		case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
>  		case KF_ARG_PTR_TO_CONST_STR:
> +		case KF_ARG_PTR_TO_TIMER:
>  			/* Trusted by default */
>  			break;
>  		default:
> @@ -11973,6 +12026,9 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
>  			if (ret)
>  				return ret;
>  			break;
> +		case KF_ARG_PTR_TO_TIMER:
> +			/* FIXME: should we do anything here? */
> +			break;
>  		}
>  	}
>  
> @@ -15591,7 +15647,9 @@ static int visit_insn(int t, struct bpf_verifier_env *env)
>  		return DONE_EXPLORING;
>  
>  	case BPF_CALL:
> -		if (insn->src_reg == 0 && insn->imm == BPF_FUNC_timer_set_callback)
> +		if (insn->src_reg == 0 &&
> +		    (insn->imm == BPF_FUNC_timer_set_callback ||
> +		     is_bpf_timer_set_sleepable_cb_kfunc(insn->imm)))
>  			/* Mark this call insn as a prune point to trigger
>  			 * is_state_visited() check before call itself is
>  			 * processed by __check_func_call(). Otherwise new
> @@ -16767,6 +16825,9 @@ static bool states_equal(struct bpf_verifier_env *env,
>  	if (old->active_rcu_lock != cur->active_rcu_lock)
>  		return false;
>  
> +	if (old->in_sleepable != cur->in_sleepable)
> +		return false;
> +
>  	/* for states to be equal callsites have to be the same
>  	 * and all frame states need to be equivalent
>  	 */
> @@ -19644,7 +19705,8 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  			continue;
>  		}
>  
> -		if (insn->imm == BPF_FUNC_timer_set_callback) {
> +		if (insn->imm == BPF_FUNC_timer_set_callback ||
> +		    is_bpf_timer_set_sleepable_cb_kfunc(insn->imm)) {
>  			/* The verifier will process callback_fn as many times as necessary
>  			 * with different maps and the register states prepared by
>  			 * set_timer_callback_state will be accurate.
> 
> -- 
> 2.43.0
>