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,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 2A190C28CBC for ; Thu, 30 Apr 2020 13:52:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 08B52208D6 for ; Thu, 30 Apr 2020 13:52:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588254755; bh=4bu4rfAJxuAOnrRC2ZlHCtAsDKCEP4KUPZLuuFxDVDI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TI70HgcAvcq4rF20pIxqi1iJfHIFiMG5f1r2z66sO4dQqBsszWeJcOiZ76M2mQqwx DKMk+uz0h6fECct9YR5ONGv8y1wQD2lyh4a0ZQL26TTP9frloJGP+JoYRgFC5MV6Zf 7I36++EvEKpANtsirWpoOx/kuUAGdgmvYyd6RrJ0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727107AbgD3Nwe (ORCPT ); Thu, 30 Apr 2020 09:52:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:32890 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728292AbgD3NwH (ORCPT ); Thu, 30 Apr 2020 09:52:07 -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 55E58208CA; Thu, 30 Apr 2020 13:52:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588254727; bh=4bu4rfAJxuAOnrRC2ZlHCtAsDKCEP4KUPZLuuFxDVDI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K2iW+NoL7vhQEpxs/DBhALfxCPCXjCm3Hv8wtNjavKnISiqiY1gRv3zZBdMp7cIQm QndFS5yjzHHke+qKFx8Fcih3PD90ABUV6qxBO7Hp5KNVmB0iZy/y7hu27AaXm9Uvd9 A7HAfnsYvFMtaV1zg3HcSlLney2e2qRZn+qdEqNs= 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 5.6 74/79] bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension Date: Thu, 30 Apr 2020 09:50:38 -0400 Message-Id: <20200430135043.19851-74-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200430135043.19851-1-sashal@kernel.org> References: <20200430135043.19851-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 4d2a7a7646026..cc9ad3892ea6b 100644 --- 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_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