From patchwork Fri May 1 13:22:49 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: 226548 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=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 68C6FC47254 for ; Fri, 1 May 2020 13:52:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42EB7205C9 for ; Fri, 1 May 2020 13:52:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588341167; bh=oV6YG3KBmVsKh2hALrLGtg4+/xaDxIwbUFVk/sCmzaY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=wSXjh+s7ZIkHYAIfgbSPeO57actxZcvLg+SzARD43s7om0Ex/GwpfOTK2LWd8bGHX PX50DS/clrF9JR2c6ftKrL+S7IbUEPN4I/eqH+HvdmtmYkgz5WcW6Xa8rXnGZkqo/Q g0Yefo3sT1I5l5qXbF5h7hos71+2jgaf4nosiWUU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730571AbgEANh1 (ORCPT ); Fri, 1 May 2020 09:37:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:36278 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730552AbgEANhU (ORCPT ); Fri, 1 May 2020 09:37:20 -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 683942173E; Fri, 1 May 2020 13:37:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588340239; bh=oV6YG3KBmVsKh2hALrLGtg4+/xaDxIwbUFVk/sCmzaY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZbCoeJ7AlBMACaOFKTJ7UVngT21btdgOjBFA0V311ZMB83+8QbMf6U8iHSenpbbdU u2gXgUKKLN6ETlDKuCs+vUW44KiS0odMHz6LrOw0M7JIAOjyp1Bokj+A9Z6yrVrhy9 GHyzBOqcnhd8dqQ9k+HHeSuclHHRRgwQ3xn6AMJQ= 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 4.19 24/46] bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension Date: Fri, 1 May 2020 15:22:49 +0200 Message-Id: <20200501131507.375996284@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200501131457.023036302@linuxfoundation.org> References: <20200501131457.023036302@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 @@ -1830,7 +1830,9 @@ 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: