From patchwork Wed Jun 19 07:17:03 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 13703467 X-Patchwork-Delegate: kuba@kernel.org Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 69E567E78E; Wed, 19 Jun 2024 07:23:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718781809; cv=none; b=d+G7L/sCFZgQ490CyAAL8bHPZ56DqSTpUwnNf2GEFOg34+lRRnAgppwtbA7/PIlUS783IRSSZ02SM3kaXxt0h6zRCfAVQL63mcnrKd5RLtSXurJQu9R3zCI2hbruNaf9g6HBypcAYZHGS2NJzK+oW8dA0ylhS7NfB1jyw9Rcn3g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718781809; c=relaxed/simple; bh=FbbAiov4OHSV7INKnGdeocZuk+klys2tkIDh/H6h8/A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hAnRfCswnTedLcdeyQRjqF7fyUnfV/W8y7KS5Ynwdj1nQZGHYoiFPXuokp3v/hOa9+xduMrDu5Tx7fJVQudgtuY7YjQHsNSBOzM/WpugwWoerPv/t07B/aKGWrPo50CGBRbxSTv2yuOJJrVfF0cY8uISuN7MGbnCoDUxRfi1I2o= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=uaMeQQlQ; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=gRRePgQo; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="uaMeQQlQ"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="gRRePgQo" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1718781805; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Xg1ApPCQGVJ8CFcoKgcEnIVTe/xamtVzkM/qsLKXD5I=; b=uaMeQQlQ9JNHJgpA7MEu7evJT9xT4ccKurCvsGzc1+r2ATOhx837t1W4g/kIdExQSxV+sn 7hnQUN5CYYpcA00JjgIA8osWz59+Xuz/1c5Csjk3cfGcUDEBrmwltnU7ggK/5fqjGR1ucx ehnzZCgYwe35YjOBQRrUY5IgJEnjVT/yibYZ4tUn7arku9xPrdS4OsrLCrTA6FDwqjxCOJ sLNHhl9R+b0plhAGyAbuw0MVilh8RMb8gk8uLZsyk90CWt+hfKu3WnaRichs0elh0Ta0IZ qiAajbPVfkpXaroq8Y6BmaLUj8DEfIQK6mPSyx5xkP+kiEPXaiO0uC4h0xOKVw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1718781805; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Xg1ApPCQGVJ8CFcoKgcEnIVTe/xamtVzkM/qsLKXD5I=; b=gRRePgQor/Den0W4kzDAWMECTQaA3J+tjeeDP5rKeL6cCVWiMkwFN7wqhko/h+nYWkWwhA SVDe1CVYRYFxSeCw== To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: "David S. Miller" , Daniel Bristot de Oliveira , Boqun Feng , Daniel Borkmann , Eric Dumazet , Frederic Weisbecker , Ingo Molnar , Jakub Kicinski , Paolo Abeni , Peter Zijlstra , Thomas Gleixner , Waiman Long , Will Deacon , Sebastian Andrzej Siewior , Alexei Starovoitov , Andrii Nakryiko , David Ahern , Hao Luo , Jiri Olsa , John Fastabend , KP Singh , Martin KaFai Lau , Song Liu , Stanislav Fomichev , Yonghong Song , bpf@vger.kernel.org Subject: [PATCH v8 net-next 12/15] seg6: Use nested-BH locking for seg6_bpf_srh_states. Date: Wed, 19 Jun 2024 09:17:03 +0200 Message-ID: <20240619072253.504963-13-bigeasy@linutronix.de> In-Reply-To: <20240619072253.504963-1-bigeasy@linutronix.de> References: <20240619072253.504963-1-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org The access to seg6_bpf_srh_states is protected by disabling preemption. Based on the code, the entry point is input_action_end_bpf() and every other function (the bpf helper functions bpf_lwt_seg6_*()), that is accessing seg6_bpf_srh_states, should be called from within input_action_end_bpf(). input_action_end_bpf() accesses seg6_bpf_srh_states first at the top of the function and then disables preemption. This looks wrong because if preemption needs to be disabled as part of the locking mechanism then the variable shouldn't be accessed beforehand. Looking at how it is used via test_lwt_seg6local.sh then input_action_end_bpf() is always invoked from softirq context. If this is always the case then the preempt_disable() statement is superfluous. If this is not always invoked from softirq then disabling only preemption is not sufficient. Replace the preempt_disable() statement with nested-BH locking. This is not an equivalent replacement as it assumes that the invocation of input_action_end_bpf() always occurs in softirq context and thus the preempt_disable() is superfluous. Add a local_lock_t the data structure and use local_lock_nested_bh() for locking. Add lockdep_assert_held() to ensure the lock is held while the per-CPU variable is referenced in the helper functions. Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: David Ahern Cc: Hao Luo Cc: Jiri Olsa Cc: John Fastabend Cc: KP Singh Cc: Martin KaFai Lau Cc: Song Liu Cc: Stanislav Fomichev Cc: Yonghong Song Cc: bpf@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior --- include/net/seg6_local.h | 1 + net/core/filter.c | 3 +++ net/ipv6/seg6_local.c | 22 ++++++++++++++-------- 3 files changed, 18 insertions(+), 8 deletions(-) diff --git a/include/net/seg6_local.h b/include/net/seg6_local.h index 3fab9dec2ec45..888c1ce6f5272 100644 --- a/include/net/seg6_local.h +++ b/include/net/seg6_local.h @@ -19,6 +19,7 @@ extern int seg6_lookup_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr, extern bool seg6_bpf_has_valid_srh(struct sk_buff *skb); struct seg6_bpf_srh_state { + local_lock_t bh_lock; struct ipv6_sr_hdr *srh; u16 hdrlen; bool valid; diff --git a/net/core/filter.c b/net/core/filter.c index 7c46ecba3b01b..ba1a739a9bedc 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6450,6 +6450,7 @@ BPF_CALL_4(bpf_lwt_seg6_store_bytes, struct sk_buff *, skb, u32, offset, void *srh_tlvs, *srh_end, *ptr; int srhoff = 0; + lockdep_assert_held(&srh_state->bh_lock); if (srh == NULL) return -EINVAL; @@ -6506,6 +6507,7 @@ BPF_CALL_4(bpf_lwt_seg6_action, struct sk_buff *, skb, int hdroff = 0; int err; + lockdep_assert_held(&srh_state->bh_lock); switch (action) { case SEG6_LOCAL_ACTION_END_X: if (!seg6_bpf_has_valid_srh(skb)) @@ -6582,6 +6584,7 @@ BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, skb, u32, offset, int srhoff = 0; int ret; + lockdep_assert_held(&srh_state->bh_lock); if (unlikely(srh == NULL)) return -EINVAL; diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c index 24e2b4b494cb0..c4828c6620f07 100644 --- a/net/ipv6/seg6_local.c +++ b/net/ipv6/seg6_local.c @@ -1380,7 +1380,9 @@ static int input_action_end_b6_encap(struct sk_buff *skb, return err; } -DEFINE_PER_CPU(struct seg6_bpf_srh_state, seg6_bpf_srh_states); +DEFINE_PER_CPU(struct seg6_bpf_srh_state, seg6_bpf_srh_states) = { + .bh_lock = INIT_LOCAL_LOCK(bh_lock), +}; bool seg6_bpf_has_valid_srh(struct sk_buff *skb) { @@ -1388,6 +1390,7 @@ bool seg6_bpf_has_valid_srh(struct sk_buff *skb) this_cpu_ptr(&seg6_bpf_srh_states); struct ipv6_sr_hdr *srh = srh_state->srh; + lockdep_assert_held(&srh_state->bh_lock); if (unlikely(srh == NULL)) return false; @@ -1408,8 +1411,7 @@ bool seg6_bpf_has_valid_srh(struct sk_buff *skb) static int input_action_end_bpf(struct sk_buff *skb, struct seg6_local_lwt *slwt) { - struct seg6_bpf_srh_state *srh_state = - this_cpu_ptr(&seg6_bpf_srh_states); + struct seg6_bpf_srh_state *srh_state; struct ipv6_sr_hdr *srh; int ret; @@ -1420,10 +1422,14 @@ static int input_action_end_bpf(struct sk_buff *skb, } advance_nextseg(srh, &ipv6_hdr(skb)->daddr); - /* preempt_disable is needed to protect the per-CPU buffer srh_state, - * which is also accessed by the bpf_lwt_seg6_* helpers + /* The access to the per-CPU buffer srh_state is protected by running + * always in softirq context (with disabled BH). On PREEMPT_RT the + * required locking is provided by the following local_lock_nested_bh() + * statement. It is also accessed by the bpf_lwt_seg6_* helpers via + * bpf_prog_run_save_cb(). */ - preempt_disable(); + local_lock_nested_bh(&seg6_bpf_srh_states.bh_lock); + srh_state = this_cpu_ptr(&seg6_bpf_srh_states); srh_state->srh = srh; srh_state->hdrlen = srh->hdrlen << 3; srh_state->valid = true; @@ -1446,15 +1452,15 @@ static int input_action_end_bpf(struct sk_buff *skb, if (srh_state->srh && !seg6_bpf_has_valid_srh(skb)) goto drop; + local_unlock_nested_bh(&seg6_bpf_srh_states.bh_lock); - preempt_enable(); if (ret != BPF_REDIRECT) seg6_lookup_nexthop(skb, NULL, 0); return dst_input(skb); drop: - preempt_enable(); + local_unlock_nested_bh(&seg6_bpf_srh_states.bh_lock); kfree_skb(skb); return -EINVAL; }