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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 52C55C43331 for ; Wed, 23 Dec 2020 02:24:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B6DA22AAF for ; Wed, 23 Dec 2020 02:24:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728462AbgLWCYK (ORCPT ); Tue, 22 Dec 2020 21:24:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:52738 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730087AbgLWCX4 (ORCPT ); Tue, 22 Dec 2020 21:23:56 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0167F22285; Wed, 23 Dec 2020 02:23:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1608690220; bh=ZyApZxQZVk6sKMiHL/zzmD4bkGQiWvE7rBwr+GXas2s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Cuw0XGTecvubsokO9T7vXKAaO1qt0x3vnhrwDcPQdegsPuy0/j7LntzYB9q22/fTH ocDLKPLydXBjpp82q/vtuialyN2eJh7Gf+uKKkOfXmMAwOCFUQEe9+K+LNbtmbUKJn HsQS3qneSDmVwrn8fp4d9+j+WRoinztpzjlIsEZl3LRf+crES4JM//3mG6/VCo0pfJ H09QptVJTQtTjZbhOeuHmC5PMDum7fsmro65Z+MS/+g62W2LEm8nmjnKXlYp7+D2hU Ut0KK4fEeQnvdW4q7dFy3K3azSQFCHpQiRJJy248MSD+J632WbUlhW99qEALuErkQc 3Eaxc41p2Zsgw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Andy Lutomirski , Borislav Petkov , Sasha Levin , linux-kselftest@vger.kernel.org Subject: [PATCH AUTOSEL 4.14 38/66] selftests/x86/fsgsbase: Fix GS == 1, 2, and 3 tests Date: Tue, 22 Dec 2020 21:22:24 -0500 Message-Id: <20201223022253.2793452-38-sashal@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20201223022253.2793452-1-sashal@kernel.org> References: <20201223022253.2793452-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski [ Upstream commit 716572b0003ef67a4889bd7d85baf5099c5a0248 ] Setting GS to 1, 2, or 3 causes a nonsensical part of the IRET microcode to change GS back to zero on a return from kernel mode to user mode. The result is that these tests fail randomly depending on when interrupts happen. Detect when this happens and let the test pass. Signed-off-by: Andy Lutomirski Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/7567fd44a1d60a9424f25b19a998f12149993b0d.1604346596.git.luto@kernel.org Signed-off-by: Sasha Levin --- tools/testing/selftests/x86/fsgsbase.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c index f249e042b3b51..026cd644360f6 100644 --- a/tools/testing/selftests/x86/fsgsbase.c +++ b/tools/testing/selftests/x86/fsgsbase.c @@ -318,8 +318,8 @@ static void set_gs_and_switch_to(unsigned long local, local = read_base(GS); /* - * Signal delivery seems to mess up weird selectors. Put it - * back. + * Signal delivery is quite likely to change a selector + * of 1, 2, or 3 back to 0 due to IRET being defective. */ asm volatile ("mov %0, %%gs" : : "rm" (force_sel)); } else { @@ -337,6 +337,14 @@ static void set_gs_and_switch_to(unsigned long local, if (base == local && sel_pre_sched == sel_post_sched) { printf("[OK]\tGS/BASE remained 0x%hx/0x%lx\n", sel_pre_sched, local); + } else if (base == local && sel_pre_sched >= 1 && sel_pre_sched <= 3 && + sel_post_sched == 0) { + /* + * IRET is misdesigned and will squash selectors 1, 2, or 3 + * to zero. Don't fail the test just because this happened. + */ + printf("[OK]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx because IRET is defective\n", + sel_pre_sched, local, sel_post_sched, base); } else { nerrs++; printf("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n", -- 2.27.0