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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 74C7AC47253 for ; Fri, 1 May 2020 13:43:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 50170208DB for ; Fri, 1 May 2020 13:43:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588340638; bh=xQhIbqv9qqbGbztx1QNd5fp99mJetbAhMqDs+wPVU+w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=rqthYLnWZN7ymKVmAUHLwEog1FaUpSsv1RJ8nK8itaP3W6qX/HbM1uNH2I0X8W+OF OppQ8vWuEmu1WgbVdR5Xbbla03ziI7wyLYc1NN6WQaU2de89bF3Fq37iiLFWjbAV1S bQmsA+p3cikHjQHmABAreilE6gOVtTK7jA38t2JI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731341AbgEANnz (ORCPT ); Fri, 1 May 2020 09:43:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:44884 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731680AbgEANnx (ORCPT ); Fri, 1 May 2020 09:43:53 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.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 06BF22051A; Fri, 1 May 2020 13:43:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588340632; bh=xQhIbqv9qqbGbztx1QNd5fp99mJetbAhMqDs+wPVU+w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0UuihE8G+GjHEDpz1fuhv3EMFWKBzR4Jb0UMR+loav+6r2cNLjr6j7Pb2NBbxjRpG KM1SF02nK0qeymr8/MbyQIhVzuMEph0R5q1CrcUi0NUZtB5oZSNY+6cbKEE2B5P9YV 9srgI8r4AQavU2f19lK9zvpajNROsbtDFpVeueQc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Xi Wang , Luke Nelson , Alexei Starovoitov , "H. Peter Anvin (Intel)" , Wang YanQing Subject: [PATCH 5.6 061/106] bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension Date: Fri, 1 May 2020 15:23:34 +0200 Message-Id: <20200501131550.891106146@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200501131543.421333643@linuxfoundation.org> References: <20200501131543.421333643@linuxfoundation.org> User-Agent: quilt/0.66 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 From: Luke Nelson commit 5fa9a98fb10380e48a398998cd36a85e4ef711d6 upstream. The current JIT uses the following sequence to zero-extend into the upper 32 bits of the destination register for BPF_LDX BPF_{B,H,W}, when the destination register is not on the stack: EMIT3(0xC7, add_1reg(0xC0, dst_hi), 0); The problem is that C7 /0 encodes a MOV instruction that requires a 4-byte immediate; the current code emits only 1 byte of the immediate. This means that the first 3 bytes of the next instruction will be treated as the rest of the immediate, breaking the stream of instructions. This patch fixes the problem by instead emitting "xor dst_hi,dst_hi" to clear the upper 32 bits. This fixes the problem and is more efficient than using MOV to load a zero immediate. This bug may not be currently triggerable as BPF_REG_AX is the only register not stored on the stack and the verifier uses it in a limited way, and the verifier implements a zero-extension optimization. But the JIT should avoid emitting incorrect encodings regardless. Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32") Signed-off-by: Xi Wang Signed-off-by: Luke Nelson Signed-off-by: Alexei Starovoitov Reviewed-by: H. Peter Anvin (Intel) Acked-by: Wang YanQing Link: https://lore.kernel.org/bpf/20200422173630.8351-1-luke.r.nels@gmail.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/net/bpf_jit_comp32.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1854,7 +1854,9 @@ static int do_jit(struct bpf_prog *bpf_p STACK_VAR(dst_hi)); EMIT(0x0, 4); } else { - EMIT3(0xC7, add_1reg(0xC0, dst_hi), 0); + /* xor dst_hi,dst_hi */ + EMIT2(0x33, + add_2reg(0xC0, dst_hi, dst_hi)); } break; case BPF_DW: