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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 5425FC07520 for ; Thu, 13 Sep 2018 13:59:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1816F20652 for ; Thu, 13 Sep 2018 13:59:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1816F20652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731724AbeIMTJT (ORCPT ); Thu, 13 Sep 2018 15:09:19 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34854 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728339AbeIMTJT (ORCPT ); Thu, 13 Sep 2018 15:09:19 -0400 Received: from localhost (ip-213-127-77-73.ip.prioritytelecom.net [213.127.77.73]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 19F25D15; Thu, 13 Sep 2018 13:59:40 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Michael Ellerman , Nicholas Piggin , Sasha Levin Subject: [PATCH 4.18 125/197] powerpc/64s: Make rfi_flush_fallback a little more robust Date: Thu, 13 Sep 2018 15:31:14 +0200 Message-Id: <20180913131846.545286473@linuxfoundation.org> X-Mailer: git-send-email 2.19.0 In-Reply-To: <20180913131841.568116777@linuxfoundation.org> References: <20180913131841.568116777@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Ellerman [ Upstream commit 78ee9946371f5848ddfc88ab1a43867df8f17d83 ] Because rfi_flush_fallback runs immediately before the return to userspace it currently runs with the user r1 (stack pointer). This means if we oops in there we will report a bad kernel stack pointer in the exception entry path, eg: Bad kernel stack pointer 7ffff7150e40 at c0000000000023b4 Oops: Bad kernel stack pointer, sig: 6 [#1] LE SMP NR_CPUS=32 NUMA PowerNV Modules linked in: CPU: 0 PID: 1246 Comm: klogd Not tainted 4.18.0-rc2-gcc-7.3.1-00175-g0443f8a69ba3 #7 NIP: c0000000000023b4 LR: 0000000010053e00 CTR: 0000000000000040 REGS: c0000000fffe7d40 TRAP: 4100 Not tainted (4.18.0-rc2-gcc-7.3.1-00175-g0443f8a69ba3) MSR: 9000000002803031 CR: 44000442 XER: 20000000 CFAR: c00000000000bac8 IRQMASK: c0000000f1e66a80 GPR00: 0000000002000000 00007ffff7150e40 00007fff93a99900 0000000000000020 ... NIP [c0000000000023b4] rfi_flush_fallback+0x34/0x80 LR [0000000010053e00] 0x10053e00 Although the NIP tells us where we were, and the TRAP number tells us what happened, it would still be nicer if we could report the actual exception rather than barfing about the stack pointer. We an do that fairly simply by loading the kernel stack pointer on entry and restoring the user value before returning. That way we see a regular oops such as: Unrecoverable exception 4100 at c00000000000239c Oops: Unrecoverable exception, sig: 6 [#1] LE SMP NR_CPUS=32 NUMA PowerNV Modules linked in: CPU: 0 PID: 1251 Comm: klogd Not tainted 4.18.0-rc3-gcc-7.3.1-00097-g4ebfcac65acd-dirty #40 NIP: c00000000000239c LR: 0000000010053e00 CTR: 0000000000000040 REGS: c0000000f1e17bb0 TRAP: 4100 Not tainted (4.18.0-rc3-gcc-7.3.1-00097-g4ebfcac65acd-dirty) MSR: 9000000002803031 CR: 44000442 XER: 20000000 CFAR: c00000000000bac8 IRQMASK: 0 ... NIP [c00000000000239c] rfi_flush_fallback+0x3c/0x80 LR [0000000010053e00] 0x10053e00 Call Trace: [c0000000f1e17e30] [c00000000000b9e4] system_call+0x5c/0x70 (unreliable) Note this shouldn't make the kernel stack pointer vulnerable to a meltdown attack, because it should be flushed from the cache before we return to userspace. The user r1 value will be in the cache, because we load it in the return path, but that is harmless. Signed-off-by: Michael Ellerman Reviewed-by: Nicholas Piggin Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kernel/exceptions-64s.S | 6 ++++++ 1 file changed, 6 insertions(+) --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1526,6 +1526,8 @@ TRAMP_REAL_BEGIN(stf_barrier_fallback) TRAMP_REAL_BEGIN(rfi_flush_fallback) SET_SCRATCH0(r13); GET_PACA(r13); + std r1,PACA_EXRFI+EX_R12(r13) + ld r1,PACAKSAVE(r13) std r9,PACA_EXRFI+EX_R9(r13) std r10,PACA_EXRFI+EX_R10(r13) std r11,PACA_EXRFI+EX_R11(r13) @@ -1560,12 +1562,15 @@ TRAMP_REAL_BEGIN(rfi_flush_fallback) ld r9,PACA_EXRFI+EX_R9(r13) ld r10,PACA_EXRFI+EX_R10(r13) ld r11,PACA_EXRFI+EX_R11(r13) + ld r1,PACA_EXRFI+EX_R12(r13) GET_SCRATCH0(r13); rfid TRAMP_REAL_BEGIN(hrfi_flush_fallback) SET_SCRATCH0(r13); GET_PACA(r13); + std r1,PACA_EXRFI+EX_R12(r13) + ld r1,PACAKSAVE(r13) std r9,PACA_EXRFI+EX_R9(r13) std r10,PACA_EXRFI+EX_R10(r13) std r11,PACA_EXRFI+EX_R11(r13) @@ -1600,6 +1605,7 @@ TRAMP_REAL_BEGIN(hrfi_flush_fallback) ld r9,PACA_EXRFI+EX_R9(r13) ld r10,PACA_EXRFI+EX_R10(r13) ld r11,PACA_EXRFI+EX_R11(r13) + ld r1,PACA_EXRFI+EX_R12(r13) GET_SCRATCH0(r13); hrfid