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=-10.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,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 CE4D4C43441 for ; Mon, 19 Nov 2018 22:45:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 950CE214DA for ; Mon, 19 Nov 2018 22:45:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="iLPB/Jvq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 950CE214DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1731859AbeKTJLm (ORCPT ); Tue, 20 Nov 2018 04:11:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:44840 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731725AbeKTJLl (ORCPT ); Tue, 20 Nov 2018 04:11:41 -0500 Received: from localhost (c-71-205-112-160.hsd1.co.comcast.net [71.205.112.160]) (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 A45052148E; Mon, 19 Nov 2018 22:45:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542667547; bh=Z/QmCvuEDR0yIFKfuIsoKI7xQ7oBVS02ijKpwVL9eqo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:In-Reply-To: References:From; b=iLPB/Jvqapnf5A4a0F6wQe0m4s1OaLC++EM+5zFFfgNi0z69ze9/yHqnIXVTO/bwK AeEZt0110XnXR59XV73z3PgJeXmUf0u+GPmkKMyNahn63kFPMIDsERikoZ5uWQgCWx vLQ0DjdxuqzAjfh3jzhbfztfI8Z25k+54zKYzt8U= From: Andy Lutomirski To: x86@kernel.org Cc: LKML , Yu-cheng Yu , Dave Hansen , Peter Zijlstra , Borislav Petkov , Andy Lutomirski Subject: [PATCH 07/13] x86/fault: Make error_code sanitization more robust Date: Mon, 19 Nov 2018 14:45:31 -0800 Message-Id: X-Mailer: git-send-email 2.17.2 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The error code in a page fault on a kernel address indicates whether that address is mapped, which should not be revealed in a signal. The normal code path for a page fault on a kernel address sanitizes the bit, but the paths for vsyscall emulation and SIGBUS do not. Both are harmless, but for subtle reasons. SIGBUS is never sent for a kernel address, and vsyscall emulation will never fault on a kernel address per se because it will fail an access_ok() check instead. Make the code more robust by adding a helper that sets the relevant fields and sanitizing the error code in the helper. This also cleans up the code -- we had three copies of roughly the same thing. Signed-off-by: Andy Lutomirski --- arch/x86/mm/fault.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index bd89b6f83aa2..fac931d89c23 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -631,6 +631,24 @@ pgtable_bad(struct pt_regs *regs, unsigned long error_code, oops_end(flags, regs, sig); } +static void set_signal_archinfo(unsigned long address, + unsigned long error_code) +{ + struct task_struct *tsk = current; + + /* + * To avoid leaking information about the kernel page + * table layout, pretend that user-mode accesses to + * kernel addresses are always protection faults. + */ + if (address >= TASK_SIZE_MAX) + error_code |= X86_PF_PROT; + + tsk->thread.trap_nr = X86_TRAP_PF; + tsk->thread.error_code = error_code | X86_PF_USER; + tsk->thread.cr2 = address; +} + static noinline void no_context(struct pt_regs *regs, unsigned long error_code, unsigned long address, int signal, int si_code) @@ -656,9 +674,7 @@ no_context(struct pt_regs *regs, unsigned long error_code, * faulting through the emulate_vsyscall() logic. */ if (current->thread.sig_on_uaccess_err && signal) { - tsk->thread.trap_nr = X86_TRAP_PF; - tsk->thread.error_code = error_code | X86_PF_USER; - tsk->thread.cr2 = address; + set_signal_archinfo(address, error_code); /* XXX: hwpoison faults will set the wrong code. */ force_sig_fault(signal, si_code, (void __user *)address, @@ -821,9 +837,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, if (likely(show_unhandled_signals)) show_signal_msg(regs, error_code, address, tsk); - tsk->thread.cr2 = address; - tsk->thread.error_code = error_code; - tsk->thread.trap_nr = X86_TRAP_PF; + set_signal_archinfo(address, error_code); if (si_code == SEGV_PKUERR) force_sig_pkuerr((void __user *)address, pkey); @@ -937,9 +951,7 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, if (is_prefetch(regs, error_code, address)) return; - tsk->thread.cr2 = address; - tsk->thread.error_code = error_code; - tsk->thread.trap_nr = X86_TRAP_PF; + set_signal_archinfo(address, error_code); #ifdef CONFIG_MEMORY_FAILURE if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { -- 2.17.2