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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2AB3C19F2D for ; Tue, 9 Aug 2022 18:07:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344890AbiHISHO (ORCPT ); Tue, 9 Aug 2022 14:07:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344757AbiHISGh (ORCPT ); Tue, 9 Aug 2022 14:06:37 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 71AFB20192; Tue, 9 Aug 2022 11:02:55 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 03BDBB8171A; Tue, 9 Aug 2022 18:02:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67F98C43470; Tue, 9 Aug 2022 18:02:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1660068172; bh=GKZ5PKCQqTqdXrWsuss0Jv7382G5VfbXuBTColpUSUw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bd2P/pI7IbN64JhdOaUW7w7+6K+L6BOV4AqHZbb1WqD/Kd5q9A3VVIZKRZEDEYpSe dFnDkGphnhi5Z3iTAYEFBPIjDXWs6lcj93qkwi6+UzOE5t1g+bwk/uarWx3mxMUJUy MgZe+B3SD1vf40YFcMVzuqvUAgHbiqeLGyG+LBoc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrew Cooper , Pawan Gupta , Borislav Petkov Subject: [PATCH 4.19 32/32] x86/speculation: Add LFENCE to RSB fill sequence Date: Tue, 9 Aug 2022 20:00:23 +0200 Message-Id: <20220809175514.089995381@linuxfoundation.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220809175513.082573955@linuxfoundation.org> References: <20220809175513.082573955@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pawan Gupta commit ba6e31af2be96c4d0536f2152ed6f7b6c11bca47 upstream. RSB fill sequence does not have any protection for miss-prediction of conditional branch at the end of the sequence. CPU can speculatively execute code immediately after the sequence, while RSB filling hasn't completed yet. #define __FILL_RETURN_BUFFER(reg, nr, sp) \ mov $(nr/2), reg; \ 771: \ call 772f; \ 773: /* speculation trap */ \ pause; \ lfence; \ jmp 773b; \ 772: \ call 774f; \ 775: /* speculation trap */ \ pause; \ lfence; \ jmp 775b; \ 774: \ dec reg; \ jnz 771b; <----- CPU can miss-predict here. \ add $(BITS_PER_LONG/8) * nr, sp; Before RSB is filled, RETs that come in program order after this macro can be executed speculatively, making them vulnerable to RSB-based attacks. Mitigate it by adding an LFENCE after the conditional branch to prevent speculation while RSB is being filled. Suggested-by: Andrew Cooper Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/nospec-branch.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -52,7 +52,9 @@ 774: \ dec reg; \ jnz 771b; \ - add $(BITS_PER_LONG/8) * nr, sp; + add $(BITS_PER_LONG/8) * nr, sp; \ + /* barrier for jnz misprediction */ \ + lfence; /* Sequence to mitigate PBRSB on eIBRS CPUs */ #define __ISSUE_UNBALANCED_RET_GUARD(sp) \