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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, 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 EEAB9C4360C for ; Mon, 17 May 2021 15:24:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0A9961040 for ; Mon, 17 May 2021 15:24:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245076AbhEQPYd (ORCPT ); Mon, 17 May 2021 11:24:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:37206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242968AbhEQPKe (ORCPT ); Mon, 17 May 2021 11:10:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 83FFD611ED; Mon, 17 May 2021 14:30:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621261838; bh=X7fnVi1hMtPjA0PV0mMJSqOArzvQZgsObfRgH3qQlt4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=L4ux1bfNevYtoqS4LIND9EzeCb4lRGaaqjUZAnPm+NNgcWu7cP7Shzhj1Bz+402OC 0IdGcAmDVdIPZs8RKrcnNWdEDBovW0ZmGcMMngKurNgkdZD8myxI7l97YR/ut9M6lw WwKxX7XsrptemeYxOBowHVLcJRpS63AATsV3HaVk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Michael Ellerman Subject: [PATCH 5.4 098/141] powerpc/64s: Fix crashes when toggling entry flush barrier Date: Mon, 17 May 2021 16:02:30 +0200 Message-Id: <20210517140246.063515305@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210517140242.729269392@linuxfoundation.org> References: <20210517140242.729269392@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: Michael Ellerman commit aec86b052df6541cc97c5fca44e5934cbea4963b upstream. The entry flush mitigation can be enabled/disabled at runtime via a debugfs file (entry_flush), which causes the kernel to patch itself to enable/disable the relevant mitigations. However depending on which mitigation we're using, it may not be safe to do that patching while other CPUs are active. For example the following crash: sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20 Shows that we returned to userspace with a corrupted LR that points into the kernel, due to executing the partially patched call to the fallback entry flush (ie. we missed the LR restore). Fix it by doing the patching under stop machine. The CPUs that aren't doing the patching will be spinning in the core of the stop machine logic. That is currently sufficient for our purposes, because none of the patching we do is to that code or anywhere in the vicinity. Fixes: f79643787e0a ("powerpc/64s: flush L1D on kernel entry") Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210506044959.1298123-2-mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/lib/feature-fixups.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -293,8 +293,9 @@ void do_uaccess_flush_fixups(enum l1d_fl : "unknown"); } -void do_entry_flush_fixups(enum l1d_flush_type types) +static int __do_entry_flush_fixups(void *data) { + enum l1d_flush_type types = *(enum l1d_flush_type *)data; unsigned int instrs[3], *dest; long *start, *end; int i; @@ -345,6 +346,19 @@ void do_entry_flush_fixups(enum l1d_flus : "ori type" : (types & L1D_FLUSH_MTTRIG) ? "mttrig type" : "unknown"); + + return 0; +} + +void do_entry_flush_fixups(enum l1d_flush_type types) +{ + /* + * The call to the fallback flush can not be safely patched in/out while + * other CPUs are executing it. So call __do_entry_flush_fixups() on one + * CPU while all other CPUs spin in the stop machine core with interrupts + * hard disabled. + */ + stop_machine(__do_entry_flush_fixups, &types, NULL); } void do_rfi_flush_fixups(enum l1d_flush_type types)