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=-16.7 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,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 7EED2C433F5 for ; Fri, 17 Sep 2021 16:58:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5DAE761212 for ; Fri, 17 Sep 2021 16:58:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245120AbhIQQ7X (ORCPT ); Fri, 17 Sep 2021 12:59:23 -0400 Received: from pegase2.c-s.fr ([93.17.235.10]:37113 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244998AbhIQQ7T (ORCPT ); Fri, 17 Sep 2021 12:59:19 -0400 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HB0WS0Bk0z9sTL; Fri, 17 Sep 2021 18:57:56 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Q-t8XLaWNuNY; Fri, 17 Sep 2021 18:57:55 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4HB0WR6B2dz9sT0; Fri, 17 Sep 2021 18:57:55 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BB3DE8B799; Fri, 17 Sep 2021 18:57:55 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id TA_mV7fAT1MU; Fri, 17 Sep 2021 18:57:55 +0200 (CEST) Received: from PO20335.IDSI0.si.c-s.fr (unknown [192.168.202.36]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 975A58B768; Fri, 17 Sep 2021 18:57:54 +0200 (CEST) Subject: Re: [PATCH v2 8/8] bpf ppc32: Add addr > TASK_SIZE_MAX explicit check To: Hari Bathini , naveen.n.rao@linux.ibm.com, mpe@ellerman.id.au, ast@kernel.org, daniel@iogearbox.net Cc: paulus@samba.org, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <20210917153047.177141-1-hbathini@linux.ibm.com> <20210917153047.177141-9-hbathini@linux.ibm.com> From: Christophe Leroy Message-ID: Date: Fri, 17 Sep 2021 18:57:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210917153047.177141-9-hbathini@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr-FR Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Le 17/09/2021 à 17:30, Hari Bathini a écrit : > With KUAP enabled, any kernel code which wants to access userspace > needs to be surrounded by disable-enable KUAP. But that is not > happening for BPF_PROBE_MEM load instruction. Though PPC32 does not > support read protection, considering the fact that PTR_TO_BTF_ID > (which uses BPF_PROBE_MEM mode) could either be a valid kernel pointer > or NULL but should never be a pointer to userspace address, execute > BPF_PROBE_MEM load only if addr > TASK_SIZE_MAX, otherwise set > dst_reg=0 and move on. Same comment as patch 6. > > This will catch NULL, valid or invalid userspace pointers. Only bad > kernel pointer will be handled by BPF exception table. > > [Alexei suggested for x86] > Suggested-by: Alexei Starovoitov > Signed-off-by: Hari Bathini > --- > > Changes in v2: > * New patch to handle bad userspace pointers on PPC32. > > > arch/powerpc/net/bpf_jit_comp32.c | 39 +++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) > > diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c > index c6262289dcc4..faa8047fcf4a 100644 > --- a/arch/powerpc/net/bpf_jit_comp32.c > +++ b/arch/powerpc/net/bpf_jit_comp32.c > @@ -821,6 +821,45 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context * > /* dst = *(u64 *)(ul) (src + off) */ > case BPF_LDX | BPF_MEM | BPF_DW: > case BPF_LDX | BPF_PROBE_MEM | BPF_DW: > + /* > + * As PTR_TO_BTF_ID that uses BPF_PROBE_MEM mode could either be a valid > + * kernel pointer or NULL but not a userspace address, execute BPF_PROBE_MEM > + * load only if addr > TASK_SIZE_MAX, otherwise set dst_reg=0 and move on. > + */ > + if (BPF_MODE(code) == BPF_PROBE_MEM) { > + bool extra_insn_needed = false; > + unsigned int adjusted_idx; > + > + /* > + * For BPF_DW case, "li reg_h,0" would be needed when > + * !fp->aux->verifier_zext. Adjust conditional branch'ing > + * address accordingly. > + */ > + if ((size == BPF_DW) && !fp->aux->verifier_zext) > + extra_insn_needed = true; Don't make it too complicated. That's a fallback that should never happen, no need to optimise. You can put that instruction all the time (or put a NOP) and keep the jumps always the same. > + > + /* > + * Need to jump two instructions instead of one for BPF_DW case > + * as there are two load instructions for dst_reg_h & dst_reg > + * respectively. > + */ > + adjusted_idx = (size == BPF_DW) ? 1 : 0; Same comment as patch 6, drop adjusted_idx and do an if/else directly for the PPC_JMP. > + > + EMIT(PPC_RAW_ADDI(b2p[TMP_REG], src_reg, off)); > + PPC_LI32(_R0, TASK_SIZE_MAX); > + EMIT(PPC_RAW_CMPLW(b2p[TMP_REG], _R0)); > + PPC_BCC(COND_GT, (ctx->idx + 4 + (extra_insn_needed ? 1 : 0)) * 4); > + EMIT(PPC_RAW_LI(dst_reg, 0)); > + /* > + * Note that "li reg_h,0" is emitted for BPF_B/H/W case, > + * if necessary. So, jump there insted of emitting an > + * additional "li reg_h,0" instruction. > + */ > + if (extra_insn_needed) > + EMIT(PPC_RAW_LI(dst_reg_h, 0)); > + PPC_JMP((ctx->idx + 2 + adjusted_idx) * 4); > + } > + > switch (size) { > case BPF_B: > EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off)); >