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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 E3068C47253 for ; Thu, 30 Apr 2020 14:01:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C52BC21775 for ; Thu, 30 Apr 2020 14:01:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588255273; bh=bZgjp+pRE/vGlH0B5qlNg+/CZHrjuHxxB2hCd/EaJQc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=pjZWpJalz1k7sNyUVe7cJLsJ1wY8hZeox4/iv4BbcNmyRk/mIQk5sDdNuuQmm3NUw uOrK39EdF+JaLPuJ+s95O9VFhj0b27R1rn6IR/Dqn00vgkkfIyKalIcjanmvVjyAw1 gEuWq+6VegeurbClAgvpVPgairoCViD4LHYUOo6M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729407AbgD3OBL (ORCPT ); Thu, 30 Apr 2020 10:01:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:36058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728863AbgD3NyA (ORCPT ); Thu, 30 Apr 2020 09:54:00 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 94BB920873; Thu, 30 Apr 2020 13:53:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588254839; bh=bZgjp+pRE/vGlH0B5qlNg+/CZHrjuHxxB2hCd/EaJQc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NvAsRYftw4OXe/IU7lplZ3CSAi4SbwwMLKk3eMkJamUEzbc6LwbROg87KLZqC56BZ 8/lEGU9xNJPDOW/Tku1xCJDVYxlE5eOcKnR9vFX5wuNeUaHT1tnkukg3PUgsoLvAdW VeW3PJ3eJIX4HOySjJ4WDfGLYM+T64/rZJhktu5s= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Luke Nelson , Xi Wang , Luke Nelson , Alexei Starovoitov , "H . Peter Anvin" , Wang YanQing , Sasha Levin , netdev@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 30/30] bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension Date: Thu, 30 Apr 2020 09:53:25 -0400 Message-Id: <20200430135325.20762-30-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200430135325.20762-1-sashal@kernel.org> References: <20200430135325.20762-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Luke Nelson [ Upstream commit 5fa9a98fb10380e48a398998cd36a85e4ef711d6 ] 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: Sasha Levin --- arch/x86/net/bpf_jit_comp32.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c index 24d573bc550d9..21df0b6d7be6e 100644 --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1830,7 +1830,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 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: -- 2.20.1