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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT 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 04493C169C4 for ; Tue, 29 Jan 2019 11:41:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6B3520857 for ; Tue, 29 Jan 2019 11:41:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548762093; bh=UgYpG/Ar/WbSpZn6/XK4yvK1C6JTAc+ILXlkVOnQiN8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vdHrjvVbj08TwZvaAyaY179Mvb1Dht0+kB9Q3q/QSa32fzTyQX37Hh+kMSJ3eLlx1 uJXED/PMyJPPBv5C+9GrjQQI9cFV+JEOjb+4Lz1Dw8qBte48foP8xzwyL5hJ61ol3X AGosaMN3VoOiAzmvgYaOmqDAT25j6HG7BgiooD5Y= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729278AbfA2Llc (ORCPT ); Tue, 29 Jan 2019 06:41:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:58860 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728044AbfA2Lla (ORCPT ); Tue, 29 Jan 2019 06:41:30 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8141320882; Tue, 29 Jan 2019 11:41:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548762090; bh=UgYpG/Ar/WbSpZn6/XK4yvK1C6JTAc+ILXlkVOnQiN8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ry1unJBCl8XrVlj2pWf8S6zb/xWaYMxxXCfVz+CTMKbTNy68ayA4Nwv5CC57QpFPm PzNPxjmnh8V103REIXjnR/2dpBFlSLHs2nqgQjZ5odAtL7dOuqaDWvV/64lEf7ud65 HU5wEkQZErpYZm++FMDt2qO1/avg8MWEQOEJCoe0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Borkmann , Alexei Starovoitov , Sasha Levin Subject: [PATCH 4.20 098/117] bpf: enable access to ax register also from verifier rewrite Date: Tue, 29 Jan 2019 12:35:49 +0100 Message-Id: <20190129113212.273377554@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190129113207.477505932@linuxfoundation.org> References: <20190129113207.477505932@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ commit 9b73bfdd08e73231d6a90ae6db4b46b3fbf56c30 upstream ] Right now we are using BPF ax register in JIT for constant blinding as well as in interpreter as temporary variable. Verifier will not be able to use it simply because its use will get overridden from the former in bpf_jit_blind_insn(). However, it can be made to work in that blinding will be skipped if there is prior use in either source or destination register on the instruction. Taking constraints of ax into account, the verifier is then open to use it in rewrites under some constraints. Note, ax register already has mappings in every eBPF JIT. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Signed-off-by: Sasha Levin --- include/linux/filter.h | 7 +------ kernel/bpf/core.c | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 6 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index 68b97eda236d..b776626aeb84 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -53,12 +53,7 @@ struct sock_reuseport; #define BPF_REG_D BPF_REG_8 /* data, callee-saved */ #define BPF_REG_H BPF_REG_9 /* hlen, callee-saved */ -/* Kernel hidden auxiliary/helper register for hardening step. - * Only used by eBPF JITs. It's nothing more than a temporary - * register that JITs use internally, only that here it's part - * of eBPF instructions that have been rewritten for blinding - * constants. See JIT pre-step in bpf_jit_blind_constants(). - */ +/* Kernel hidden auxiliary/helper register. */ #define BPF_REG_AX MAX_BPF_REG #define MAX_BPF_EXT_REG (MAX_BPF_REG + 1) #define MAX_BPF_JIT_REG MAX_BPF_EXT_REG diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index ada876048ca4..ac44653025ad 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -727,6 +727,26 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, BUILD_BUG_ON(BPF_REG_AX + 1 != MAX_BPF_JIT_REG); BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG); + /* Constraints on AX register: + * + * AX register is inaccessible from user space. It is mapped in + * all JITs, and used here for constant blinding rewrites. It is + * typically "stateless" meaning its contents are only valid within + * the executed instruction, but not across several instructions. + * There are a few exceptions however which are further detailed + * below. + * + * Constant blinding is only used by JITs, not in the interpreter. + * The interpreter uses AX in some occasions as a local temporary + * register e.g. in DIV or MOD instructions. + * + * In restricted circumstances, the verifier can also use the AX + * register for rewrites as long as they do not interfere with + * the above cases! + */ + if (from->dst_reg == BPF_REG_AX || from->src_reg == BPF_REG_AX) + goto out; + if (from->imm == 0 && (from->code == (BPF_ALU | BPF_MOV | BPF_K) || from->code == (BPF_ALU64 | BPF_MOV | BPF_K))) { -- 2.19.1