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 1EB43C433F5 for ; Fri, 17 Sep 2021 16:50:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0033960EFF for ; Fri, 17 Sep 2021 16:50:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240313AbhIQQwD (ORCPT ); Fri, 17 Sep 2021 12:52:03 -0400 Received: from pegase2.c-s.fr ([93.17.235.10]:38521 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232180AbhIQQwD (ORCPT ); Fri, 17 Sep 2021 12:52:03 -0400 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HB0M348tfz9sTL; Fri, 17 Sep 2021 18:50:39 +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 LC-caAVKimfd; Fri, 17 Sep 2021 18:50:39 +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 4HB0M338ztz9sT0; Fri, 17 Sep 2021 18:50:39 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 585B08B799; Fri, 17 Sep 2021 18:50:39 +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 LUbXjviGP9Hi; Fri, 17 Sep 2021 18:50:39 +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 1BABC8B768; Fri, 17 Sep 2021 18:50:38 +0200 (CEST) Subject: Re: [PATCH v2 6/8] bpf ppc64: 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, Ravi Bangoria References: <20210917153047.177141-1-hbathini@linux.ibm.com> <20210917153047.177141-7-hbathini@linux.ibm.com> From: Christophe Leroy Message-ID: Date: Fri, 17 Sep 2021 18:50:37 +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: <20210917153047.177141-7-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 : > From: Ravi Bangoria > > On PPC64 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. > So, when BPF program tries to access invalid userspace address, > page-fault handler considers it as bad KUAP fault: > > Kernel attempted to read user page (d0000000) - exploit attempt? (uid: 0) > > 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. You should do like copy_from_kernel_nofault_allowed() and use the same criterias as is_kernel_addr() instead of using TASK_SIZE_MAX. > > 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: Ravi Bangoria > Signed-off-by: Hari Bathini > --- > > Changes in v2: > * Refactored the code based on Christophe's comments. > > > arch/powerpc/net/bpf_jit_comp64.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c > index 2fc10995f243..eb28dbc67151 100644 > --- a/arch/powerpc/net/bpf_jit_comp64.c > +++ b/arch/powerpc/net/bpf_jit_comp64.c > @@ -769,6 +769,29 @@ 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) { > + unsigned int adjusted_idx; > + > + /* > + * Check if 'off' is word aligned because PPC_BPF_LL() > + * (BPF_DW case) generates two instructions if 'off' is not > + * word-aligned and one instruction otherwise. > + */ > + adjusted_idx = ((BPF_SIZE(code) == BPF_DW) && (off & 3)) ? 1 : 0; No need of ( ) around 'BPF_SIZE(code) == BPF_DW' > + > + EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off)); > + PPC_LI64(b2p[TMP_REG_2], TASK_SIZE_MAX); > + EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2])); > + PPC_BCC(COND_GT, (ctx->idx + 4) * 4); > + EMIT(PPC_RAW_LI(dst_reg, 0)); > + PPC_JMP((ctx->idx + 2 + adjusted_idx) * 4); I think it would be more explicit if you drop adjusted_idx and do : if (BPF_SIZE(code) == BPF_DW) && (off & 3) PPC_JMP((ctx->idx + 3) * 4); else PPC_JMP((ctx->idx + 2) * 4); > + } > + > switch (size) { > case BPF_B: > EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off)); >