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From: Benjamin Tissoires <bentiss@kernel.org>
Date: Mon, 08 Apr 2024 10:09:29 +0200
Subject: [PATCH RFC bpf-next v6 4/6] bpf/helpers: mark the callback of
 bpf_timer_set_sleepable_cb() as sleepable
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Message-Id: <20240408-hid-bpf-sleepable-v6-4-0499ddd91b94@kernel.org>
References: <20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org>
In-Reply-To: <20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org>
To: Alexei Starovoitov <ast@kernel.org>, 
 Daniel Borkmann <daniel@iogearbox.net>, 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>, 
 John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
 Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
 Jiri Olsa <jolsa@kernel.org>, Mykola Lysenko <mykolal@fb.com>, 
 Shuah Khan <shuah@kernel.org>
Cc: Benjamin Tissoires <bentiss@kernel.org>, bpf@vger.kernel.org, 
 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org

Now that we have bpf_timer_set_sleepable_cb() available and working, we
can tag the attached callback as sleepable, and let the verifier check
in the correct context the calls and kfuncs.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

---

no changes in v6

no changes in v5

changes in v4:
- use a function parameter to forward the sleepable information

new in v3 (split from v2 02/10)
---
 include/linux/bpf_verifier.h |  1 +
 kernel/bpf/verifier.c        | 13 ++++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7cb1b75eee38..14e4ee67b694 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;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 00ac3a3a5f01..b75a8aca6ec9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1434,6 +1434,7 @@ 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;
@@ -2407,7 +2408,7 @@ static void init_func_state(struct bpf_verifier_env *env,
 /* Similar to push_stack(), but for async callbacks */
 static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env,
 						int insn_idx, int prev_insn_idx,
-						int subprog)
+						int subprog, bool is_sleepable)
 {
 	struct bpf_verifier_stack_elem *elem;
 	struct bpf_func_state *frame;
@@ -2434,6 +2435,7 @@ 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 = is_sleepable;
 	frame = kzalloc(sizeof(*frame), GFP_KERNEL);
 	if (!frame)
 		goto err;
@@ -5279,7 +5281,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
 
 static bool in_sleepable(struct bpf_verifier_env *env)
 {
-	return env->prog->sleepable;
+	return env->prog->sleepable ||
+	       (env->cur_state && env->cur_state->in_sleepable);
 }
 
 /* The non-sleepable programs and sleepable programs with explicit bpf_rcu_read_lock()
@@ -9497,7 +9500,8 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins
 		/* there is no real recursion here. timer callbacks are async */
 		env->subprog_info[subprog].is_async_cb = true;
 		async_cb = push_async_cb(env, env->subprog_info[subprog].start,
-					 insn_idx, subprog);
+					 insn_idx, subprog,
+					 is_bpf_timer_set_sleepable_cb_impl_kfunc(insn->imm));
 		if (!async_cb)
 			return -EFAULT;
 		callee = async_cb->frame[0];
@@ -16947,6 +16951,9 @@ 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
 	 */

-- 
2.44.0