From patchwork Fri May 1 13:23:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 226634 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,URIBL_BLOCKED,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 98517C47254 for ; Fri, 1 May 2020 13:39:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 725082495A for ; Fri, 1 May 2020 13:39:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588340394; bh=xQhIbqv9qqbGbztx1QNd5fp99mJetbAhMqDs+wPVU+w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ScRKBsNUyGSc+vWKew81WJzcDkfxoDEJgOhLBNrJdAk0wioNNcBE2O34/9q7LmLuM zl/Y+bgx6Nl5G5p9eroz+j9J6BsxuHFQjevHeJLhgkAtVp6wA1XaRROc5UtOtA2SF5 z7/2zxvwcdv71s0RQT57n2PZowQnwTmxzspUbOUY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730944AbgEANjx (ORCPT ); Fri, 1 May 2020 09:39:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:39700 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731233AbgEANjv (ORCPT ); Fri, 1 May 2020 09:39:51 -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 87B34216FD; Fri, 1 May 2020 13:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588340391; bh=xQhIbqv9qqbGbztx1QNd5fp99mJetbAhMqDs+wPVU+w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eDl596X0aJwcUV7Wy+vIqV+8DaNCkTqV9Lp4hy1jac0bH0RlN9yHt7yNDkeWM2MPB f6I3IV4A4dyN4GPsmnsuleAvo8Pn5D+MmBUCjw3lHvw+wDkv7SWTBZVlqkf+ZDuNNY 7hPJgO4P5eCcB7DsCmIBDFpr0m5bGzVrao0uJFjs= 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 5.4 47/83] bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension Date: Fri, 1 May 2020 15:23:26 +0200 Message-Id: <20200501131537.251370260@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200501131524.004332640@linuxfoundation.org> References: <20200501131524.004332640@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 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: