From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4DF79C4321E for ; Sat, 3 Dec 2022 03:00:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:CC:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ht+n1gU3hIxFryLOj5/XzCTuown6Oc2bBr/rvtKxrnI=; b=DQwwK1GFmgW3U/Q1AFJE9w7wPf AYxPYQGSsKDM3fYw7CQKNx/J+L3mkBy5ha7UdwgT48KXH4JBxkpgsd2ySfcRpghoG6kMgPGx8FnrL Dr345tTXgLdllqIDG9rFh2z48+8rDcXnYMKeyTma2ddlyM5FwCMUDJAdBJFbIvxb8lExz0wqOkTiF RvK4ALPY1jeRvGv+67vMzKPWI/YGOyp4kUBmtf4gz+Pyk78/beQJUPCysXZ+/VTMFSBa/ND/1SBoO ZdjGYYhY5fzRi7CqYo3kOizxtMg4aNKe431u6e4MPWF9FEReXNlPJ4GaxLT6umy+1zMWBCN29WFHl WnfID+Ag==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1p1Ik5-0029AF-2W; Sat, 03 Dec 2022 02:59:05 +0000 Received: from szxga02-in.huawei.com ([45.249.212.188]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1p1Ik0-00298K-Rj for linux-arm-kernel@lists.infradead.org; Sat, 03 Dec 2022 02:59:03 +0000 Received: from kwepemm600003.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4NPDyK1nTszFprd; Sat, 3 Dec 2022 10:58:01 +0800 (CST) Received: from [10.67.111.205] (10.67.111.205) by kwepemm600003.china.huawei.com (7.193.23.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 3 Dec 2022 10:58:44 +0800 Subject: Re: [PATCH bpf-next v3 1/4] bpf: Adapt 32-bit return value kfunc for 32-bit ARM when zext extension To: Alexei Starovoitov CC: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shubham Bansal , Russell King , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Mykola Lysenko , Shuah Khan , Benjamin Tissoires , Kumar Kartikeya Dwivedi , , Artem Savkov , Delyan Kratunov , bpf , linux-arm-kernel , LKML , Network Development , "open list:KERNEL SELFTEST FRAMEWORK" References: <20221126094530.226629-1-yangjihong1@huawei.com> <20221126094530.226629-2-yangjihong1@huawei.com> <20221128015758.aekybr3qlahfopwq@MacBook-Pro-5.local> From: Yang Jihong Message-ID: <8cb54255-4dce-6d50-d6f0-ac9af0e56f37@huawei.com> Date: Sat, 3 Dec 2022 10:58:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Originating-IP: [10.67.111.205] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221202_185901_265329_6423E03B X-CRM114-Status: GOOD ( 25.84 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2022/11/29 0:41, Alexei Starovoitov wrote: > On Mon, Nov 28, 2022 at 4:40 AM Yang Jihong wrote: >> >> >> >> On 2022/11/28 9:57, Alexei Starovoitov wrote: >>> On Sat, Nov 26, 2022 at 05:45:27PM +0800, Yang Jihong wrote: >>>> For ARM32 architecture, if data width of kfunc return value is 32 bits, >>>> need to do explicit zero extension for high 32-bit, insn_def_regno should >>>> return dst_reg for BPF_JMP type of BPF_PSEUDO_KFUNC_CALL. Otherwise, >>>> opt_subreg_zext_lo32_rnd_hi32 returns -EFAULT, resulting in BPF failure. >>>> >>>> Signed-off-by: Yang Jihong >>>> --- >>>> kernel/bpf/verifier.c | 44 ++++++++++++++++++++++++++++++++++++++++--- >>>> 1 file changed, 41 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>>> index 264b3dc714cc..193ea927aa69 100644 >>>> --- a/kernel/bpf/verifier.c >>>> +++ b/kernel/bpf/verifier.c >>>> @@ -1927,6 +1927,21 @@ find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset) >>>> sizeof(tab->descs[0]), kfunc_desc_cmp_by_id_off); >>>> } >>>> >>>> +static int kfunc_desc_cmp_by_imm(const void *a, const void *b); >>>> + >>>> +static const struct bpf_kfunc_desc * >>>> +find_kfunc_desc_by_imm(const struct bpf_prog *prog, s32 imm) >>>> +{ >>>> + struct bpf_kfunc_desc desc = { >>>> + .imm = imm, >>>> + }; >>>> + struct bpf_kfunc_desc_tab *tab; >>>> + >>>> + tab = prog->aux->kfunc_tab; >>>> + return bsearch(&desc, tab->descs, tab->nr_descs, >>>> + sizeof(tab->descs[0]), kfunc_desc_cmp_by_imm); >>>> +} >>>> + >>>> static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env, >>>> s16 offset) >>>> { >>>> @@ -2342,6 +2357,13 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn, >>>> */ >>>> if (insn->src_reg == BPF_PSEUDO_CALL) >>>> return false; >>>> + >>>> + /* Kfunc call will reach here because of insn_has_def32, >>>> + * conservatively return TRUE. >>>> + */ >>>> + if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) >>>> + return true; >>>> + >>>> /* Helper call will reach here because of arg type >>>> * check, conservatively return TRUE. >>>> */ >>>> @@ -2405,10 +2427,26 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn, >>>> } >>>> >>>> /* Return the regno defined by the insn, or -1. */ >>>> -static int insn_def_regno(const struct bpf_insn *insn) >>>> +static int insn_def_regno(struct bpf_verifier_env *env, const struct bpf_insn *insn) >>>> { >>>> switch (BPF_CLASS(insn->code)) { >>>> case BPF_JMP: >>>> + if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) { >>>> + const struct bpf_kfunc_desc *desc; >>>> + >>>> + /* The value of desc cannot be NULL */ >>>> + desc = find_kfunc_desc_by_imm(env->prog, insn->imm); >>>> + >>>> + /* A kfunc can return void. >>>> + * The btf type of the kfunc's return value needs >>>> + * to be checked against "void" first >>>> + */ >>>> + if (desc->func_model.ret_size == 0) >>>> + return -1; >>>> + else >>>> + return insn->dst_reg; >>>> + } >>>> + fallthrough; >>> >>> I cannot make any sense of this patch. >>> insn->dst_reg above is 0. >>> The kfunc call doesn't define a register from insn_def_regno() pov. >>> >>> Are you hacking insn_def_regno() to return 0 so that >>> if (WARN_ON(load_reg == -1)) { >>> verbose(env, "verifier bug. zext_dst is set, but no reg is defined\n"); >>> return -EFAULT; >>> } >>> in opt_subreg_zext_lo32_rnd_hi32() doesn't trigger ? >>> >>> But this verifier message should have been a hint that you need >>> to analyze why zext_dst is set on this kfunc call. >>> Maybe it shouldn't ? >>> Did you analyze the logic of mark_btf_func_reg_size() ? >> make r0 zext is not caused by mark_btf_func_reg_size. >> >> This problem occurs when running the kfunc_call_test_ref_btf_id test >> case in the 32-bit ARM environment. > > Why is it not failing on x86-32 ? Use the latest mainline kernel code to test on the x86_32 machine. The test also fails: # ./test_progs -t kfunc_call/kfunc_call_test_ref_btf_id Failed to load bpf_testmod.ko into the kernel: -8 WARNING! Selftests relying on bpf_testmod.ko will be skipped. libbpf: prog 'kfunc_call_test_ref_btf_id': BPF program load failed: Bad address libbpf: prog 'kfunc_call_test_ref_btf_id': -- BEGIN PROG LOAD LOG -- processed 25 insns (limit 1000000) max_states_per_insn 0 total_states 2 peak_states 2 mark_read 1 -- END PROG LOAD LOG -- libbpf: prog 'kfunc_call_test_ref_btf_id': failed to load: -14 libbpf: failed to load object 'kfunc_call_test' libbpf: failed to load BPF skeleton 'kfunc_call_test': -14 verify_success:FAIL:skel unexpected error: -14 Therefore, this problem also exists on x86_32: "verifier bug. zext_dst is set, but no reg is defined" > >> The bpf prog is as follows: >> int kfunc_call_test_ref_btf_id(struct __sk_buff *skb) >> { >> struct prog_test_ref_kfunc *pt; >> unsigned long s = 0; >> int ret = 0; >> >> pt = bpf_kfunc_call_test_acquire(&s); >> if (pt) { >> // here, do_check clears the upper 32bits of r0 through: >> // check_alu_op >> // ->check_reg_arg >> // ->mark_insn_zext >> if (pt->a != 42 || pt->b != 108) >> ret = -1; >> bpf_kfunc_call_test_release(pt); >> } >> return ret; >> } >> >>> >>> Before producing any patches please understand the logic fully. >>> Your commit log >>> "insn_def_regno should >>> return dst_reg for BPF_JMP type of BPF_PSEUDO_KFUNC_CALL." >>> >>> Makes no sense to me, since dst_reg is unused in JMP insn. >>> There is no concept of a src or dst register in a JMP insn. >>> >>> 32-bit x86 supports calling kfuncs. See emit_kfunc_call(). >>> And we don't have this "verifier bug. zext_dst is set" issue there, right? >>> But what you're saying in the commit log: >>> "if data width of kfunc return value is 32 bits" >>> should have been applicable to x86-32 as well. >>> So please start with a test that demonstrates the issue on x86-32 and >>> then we can discuss the way to fix it. >>> >>> The patch 2 sort-of makes sense. >>> >>> For patch 3 pls add new test funcs to bpf_testmod. >>> We will move all of them from net/bpf/test_run.c to bpf_testmod eventually. >>> . >>> > . > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel