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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: davem@davemloft.net
Cc: daniel@iogearbox.net, andrii@kernel.org, netdev@vger.kernel.org,
	bpf@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH v7 bpf-next 07/11] bpf: Relax verifier recursion check.
Date: Wed, 14 Jul 2021 17:54:13 -0700	[thread overview]
Message-ID: <20210715005417.78572-8-alexei.starovoitov@gmail.com> (raw)
In-Reply-To: <20210715005417.78572-1-alexei.starovoitov@gmail.com>

From: Alexei Starovoitov <ast@kernel.org>

In the following bpf subprogram:
static int timer_cb(void *map, void *key, void *value)
{
    bpf_timer_set_callback(.., timer_cb);
}

the 'timer_cb' is a pointer to a function.
ld_imm64 insn is used to carry this pointer.
bpf_pseudo_func() returns true for such ld_imm64 insn.

Unlike bpf_for_each_map_elem() the bpf_timer_set_callback() is asynchronous.
Relax control flow check to allow such "recursion" that is seen as an infinite
loop by check_cfg(). The distinction between bpf_for_each_map_elem() the
bpf_timer_set_callback() is done in the follow up patch.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/verifier.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cb393de3c818..1511f92b4cf4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9463,8 +9463,12 @@ static int visit_func_call_insn(int t, int insn_cnt,
 		init_explored_state(env, t + 1);
 	if (visit_callee) {
 		init_explored_state(env, t);
-		ret = push_insn(t, t + insns[t].imm + 1, BRANCH,
-				env, false);
+		ret = push_insn(t, t + insns[t].imm + 1, BRANCH, env,
+				/* It's ok to allow recursion from CFG point of
+				 * view. __check_func_call() will do the actual
+				 * check.
+				 */
+				bpf_pseudo_func(insns + t));
 	}
 	return ret;
 }
-- 
2.30.2


  parent reply	other threads:[~2021-07-15  0:54 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15  0:54 [PATCH v7 bpf-next 00/11] bpf: Introduce BPF timers Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 01/11] bpf: Prepare bpf_prog_put() to be called from irq context Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 02/11] bpf: Factor out bpf_spin_lock into helpers Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 03/11] bpf: Introduce bpf timers Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 04/11] bpf: Add map side support for " Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 05/11] bpf: Prevent pointer mismatch in bpf_timer_init Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 06/11] bpf: Remember BTF of inner maps Alexei Starovoitov
2021-07-15  0:54 ` Alexei Starovoitov [this message]
2021-07-15  0:54 ` [PATCH v7 bpf-next 08/11] bpf: Implement verifier support for validation of async callbacks Alexei Starovoitov
2022-01-04 17:15   ` Kris Van Hees
2022-01-04 18:19     ` Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 09/11] bpf: Teach stack depth check about " Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 10/11] selftests/bpf: Add bpf_timer test Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 11/11] selftests/bpf: Add a test with bpf_timer in inner map Alexei Starovoitov
2021-07-15 20:40 ` [PATCH v7 bpf-next 00/11] bpf: Introduce BPF timers patchwork-bot+netdevbpf

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