From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753552AbcCLRdK (ORCPT ); Sat, 12 Mar 2016 12:33:10 -0500 Received: from mail-ob0-f170.google.com ([209.85.214.170]:35441 "EHLO mail-ob0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751883AbcCLRdD (ORCPT ); Sat, 12 Mar 2016 12:33:03 -0500 MIME-Version: 1.0 In-Reply-To: <20160312153615.GB17873@gmail.com> References: <35f2f107e0d85473a0e66c08f93d571a9c72b7fc.1457723023.git.luto@kernel.org> <20160312153615.GB17873@gmail.com> From: Andy Lutomirski Date: Sat, 12 Mar 2016 09:32:42 -0800 Message-ID: Subject: Re: [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops To: Ingo Molnar Cc: Andy Lutomirski , X86 ML , Paolo Bonzini , Peter Zijlstra , KVM list , Arjan van de Ven , xen-devel , "linux-kernel@vger.kernel.org" , Linus Torvalds , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 12, 2016 at 7:36 AM, Ingo Molnar wrote: > > * Andy Lutomirski wrote: > >> This demotes an OOPS and likely panic due to a failed non-"safe" MSR >> access to a WARN and, for RDMSR, a return value of zero. If >> panic_on_oops is set, then failed unsafe MSR accesses will still >> oops and panic. >> >> To be clear, this type of failure should *not* happen. This patch >> exists to minimize the chance of nasty undebuggable failures due on >> systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug. >> >> Signed-off-by: Andy Lutomirski >> --- >> arch/x86/include/asm/msr.h | 10 ++++++++-- >> arch/x86/mm/extable.c | 33 +++++++++++++++++++++++++++++++++ >> 2 files changed, 41 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 9dd7e4b7fcde..f310714e6e6d 100644 >> --- a/arch/x86/mm/extable.c >> +++ b/arch/x86/mm/extable.c >> @@ -49,6 +49,39 @@ 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(1, "unsafe MSR access error: RDMSR from 0x%x", >> + (unsigned int)regs->cx); > > Btw., instead of the safe/unsafe naming (which has an emotional and security > secondary attribute), shouldn't we move this over to a _check() (or _checking()) > naming instead that we do in other places in the kernel? > > I.e.: > > rdmsr(msr, l, h); > > and: > > if (rdmsr_check(msr, l, h)) { > ... > } > > and then we could name the helpers as _check() and _nocheck() - which is neutral > naming. Will do as a separate followup series. At least with this series applied, the functions named _safe all point to each other correctly. --Andy