From patchwork Sat Apr 2 14:01:37 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Lutomirski X-Patchwork-Id: 8731671 Return-Path: X-Original-To: patchwork-xen-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 525C19F7C9 for ; Sat, 2 Apr 2016 14:04:42 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5D1F72038A for ; Sat, 2 Apr 2016 14:04:41 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 58B98200F3 for ; Sat, 2 Apr 2016 14:04:40 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1amM82-0004vA-CT; Sat, 02 Apr 2016 14:02:18 +0000 Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1amM80-0004te-Su for Xen-devel@lists.xen.org; Sat, 02 Apr 2016 14:02:16 +0000 Received: from [85.158.137.68] by server-7.bemta-3.messagelabs.com id B9/EB-04060-8E0DFF65; Sat, 02 Apr 2016 14:02:16 +0000 X-Env-Sender: luto@kernel.org X-Msg-Ref: server-14.tower-31.messagelabs.com!1459605734!32630926!1 X-Originating-IP: [198.145.29.136] X-SpamReason: No, hits=0.0 required=7.0 tests= X-StarScan-Received: X-StarScan-Version: 8.11; banners=-,-,- X-VirusChecked: Checked Received: (qmail 60228 invoked from network); 2 Apr 2016 14:02:15 -0000 Received: from mail.kernel.org (HELO mail.kernel.org) (198.145.29.136) by server-14.tower-31.messagelabs.com with DHE-RSA-AES256-GCM-SHA384 encrypted SMTP; 2 Apr 2016 14:02:15 -0000 Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id B6D2C203AB; Sat, 2 Apr 2016 14:02:12 +0000 (UTC) Received: from localhost (unknown [209.118.255.66]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B3D6D20396; Sat, 2 Apr 2016 14:02:11 +0000 (UTC) From: Andy Lutomirski To: X86 ML Date: Sat, 2 Apr 2016 07:01:37 -0700 Message-Id: <26567b216aae70e795938f4b567eace5a0eb90ba.1459605520.git.luto@kernel.org> X-Mailer: git-send-email 2.5.5 In-Reply-To: References: In-Reply-To: References: X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Cc: KVM list , Peter Zijlstra , Linus Torvalds , linux-kernel@vger.kernel.org, xen-devel , Borislav Petkov , Andy Lutomirski , Paolo Bonzini , Andrew Morton , Arjan van de Ven Subject: [Xen-devel] [PATCH v5 6/9] x86/msr: Carry on after a non-"safe" MSR access fails X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP This demotes an OOPS and likely panic due to a failed non-"safe" MSR access to a WARN_ONCE and, for RDMSR, a return value of zero. To be clear, this type of failure should *not* happen. This patch exists to minimize the chance of nasty undebuggable failures happening when a CONFIG_PARAVIRT=y bug in the non-"safe" MSR helpers gets fixed. Signed-off-by: Andy Lutomirski --- arch/x86/include/asm/msr.h | 10 ++++++++-- arch/x86/mm/extable.c | 27 +++++++++++++++++++++++++++ 2 files changed, 35 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 93fb7c1cffda..1487054a1a70 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -92,7 +92,10 @@ static inline unsigned long long native_read_msr(unsigned int msr) { DECLARE_ARGS(val, low, high); - asm volatile("rdmsr" : EAX_EDX_RET(val, low, high) : "c" (msr)); + asm volatile("1: rdmsr\n" + "2:\n" + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_rdmsr_unsafe) + : EAX_EDX_RET(val, low, high) : "c" (msr)); if (msr_tracepoint_active(__tracepoint_read_msr)) do_trace_read_msr(msr, EAX_EDX_VAL(val, low, high), 0); return EAX_EDX_VAL(val, low, high); @@ -119,7 +122,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr, static inline void native_write_msr(unsigned int msr, unsigned low, unsigned high) { - asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory"); + asm volatile("1: wrmsr\n" + "2:\n" + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe) + : : "c" (msr), "a"(low), "d" (high) : "memory"); if (msr_tracepoint_active(__tracepoint_read_msr)) do_trace_write_msr(msr, ((u64)high << 32 | low), 0); } diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 50dfe438bd91..98b5f45d9d79 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -50,6 +50,33 @@ bool ex_handler_ext(const struct exception_table_entry *fixup, } EXPORT_SYMBOL(ex_handler_ext); +bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, + struct pt_regs *regs, int trapnr) +{ + WARN_ONCE(1, "unchecked MSR access error: RDMSR from 0x%x\n", + (unsigned int)regs->cx); + + /* Pretend that the read succeeded and returned 0. */ + regs->ip = ex_fixup_addr(fixup); + regs->ax = 0; + regs->dx = 0; + return true; +} +EXPORT_SYMBOL(ex_handler_rdmsr_unsafe); + +bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup, + struct pt_regs *regs, int trapnr) +{ + WARN_ONCE(1, "unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x)\n", + (unsigned int)regs->cx, + (unsigned int)regs->dx, (unsigned int)regs->ax); + + /* Pretend that the write succeeded. */ + regs->ip = ex_fixup_addr(fixup); + return true; +} +EXPORT_SYMBOL(ex_handler_wrmsr_unsafe); + bool ex_has_fault_handler(unsigned long ip) { const struct exception_table_entry *e;