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 X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F139C4361B for ; Mon, 14 Dec 2020 21:27:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24E662078B for ; Mon, 14 Dec 2020 21:27:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2503587AbgLNV1Z (ORCPT ); Mon, 14 Dec 2020 16:27:25 -0500 Received: from www62.your-server.de ([213.133.104.62]:56128 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2503444AbgLNV1Z (ORCPT ); Mon, 14 Dec 2020 16:27:25 -0500 Received: from sslproxy06.your-server.de ([78.46.172.3]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1kovMi-000D6h-4L; Mon, 14 Dec 2020 22:26:44 +0100 Received: from [85.7.101.30] (helo=pc-9.home) by sslproxy06.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kovMh-000WRA-Uv; Mon, 14 Dec 2020 22:26:43 +0100 Subject: Re: [PATCH bpf-next v3 1/2] bpf: permits pointers on stack for helper calls To: Yonghong Song , bpf@vger.kernel.org Cc: Alexei Starovoitov , kernel-team@fb.com, Song Liu References: <20201211034121.3452172-1-yhs@fb.com> <20201211034121.3452243-1-yhs@fb.com> From: Daniel Borkmann Message-ID: Date: Mon, 14 Dec 2020 22:26:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20201211034121.3452243-1-yhs@fb.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.4/26017/Mon Dec 14 15:33:39 2020) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 12/11/20 4:41 AM, Yonghong Song wrote: > Currently, when checking stack memory accessed by helper calls, > for spills, only PTR_TO_BTF_ID and SCALAR_VALUE are > allowed. > > Song discovered an issue where the below bpf program > int dump_task(struct bpf_iter__task *ctx) > { > struct seq_file *seq = ctx->meta->seq; > static char[] info = "abc"; > BPF_SEQ_PRINTF(seq, "%s\n", info); > return 0; > } > may cause a verifier failure. > > The verifier output looks like: > ; struct seq_file *seq = ctx->meta->seq; > 1: (79) r1 = *(u64 *)(r1 +0) > ; BPF_SEQ_PRINTF(seq, "%s\n", info); > 2: (18) r2 = 0xffff9054400f6000 > 4: (7b) *(u64 *)(r10 -8) = r2 > 5: (bf) r4 = r10 > ; > 6: (07) r4 += -8 > ; BPF_SEQ_PRINTF(seq, "%s\n", info); > 7: (18) r2 = 0xffff9054400fe000 > 9: (b4) w3 = 4 > 10: (b4) w5 = 8 > 11: (85) call bpf_seq_printf#126 > R1_w=ptr_seq_file(id=0,off=0,imm=0) R2_w=map_value(id=0,off=0,ks=4,vs=4,imm=0) > R3_w=inv4 R4_w=fp-8 R5_w=inv8 R10=fp0 fp-8_w=map_value > last_idx 11 first_idx 0 > regs=8 stack=0 before 10: (b4) w5 = 8 > regs=8 stack=0 before 9: (b4) w3 = 4 > invalid indirect read from stack off -8+0 size 8 > > Basically, the verifier complains the map_value pointer at "fp-8" location. > To fix the issue, if env->allow_ptr_leaks is true, let us also permit > pointers on the stack to be accessible by the helper. > > Suggested-by: Alexei Starovoitov > Reported-by: Song Liu > Signed-off-by: Yonghong Song > --- > kernel/bpf/verifier.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 93def76cf32b..eebb2d3e16bf 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -3769,7 +3769,9 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, > goto mark; > > if (state->stack[spi].slot_type[0] == STACK_SPILL && > - state->stack[spi].spilled_ptr.type == SCALAR_VALUE) { > + (state->stack[spi].spilled_ptr.type == SCALAR_VALUE || > + (state->stack[spi].spilled_ptr.type != NOT_INIT && Thinking more on this, your v2 was actually correct since in such case stype would have been STACK_MISC or STACK_ZERO and we would have jumped to goto mark here instead, so the above is not reachable under NOT_INIT. Anyway, I took the v2 in, thanks! > + env->allow_ptr_leaks))) { > __mark_reg_unknown(env, &state->stack[spi].spilled_ptr); > for (j = 0; j < BPF_REG_SIZE; j++) > state->stack[spi].slot_type[j] = STACK_MISC; >