From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH v2 5/6] x86/hvm: Forced Emulation Prefix for debug builds of Xen Date: Wed, 24 Sep 2014 13:56:33 +0100 Message-ID: <5422BF81.3040402@citrix.com> References: <5421AD660200007800037D4D@mail.emea.novell.com> <1411488577-11705-1-git-send-email-andrew.cooper3@citrix.com> <5421B9DC.20805@oracle.com> <5421BAA0.4050209@citrix.com> <5421D543.8020600@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5421D543.8020600@oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Boris Ostrovsky , Xen-devel Cc: Kevin Tian , Keir Fraser , Suravee Suthikulpanit , Eddie Dong , Jan Beulich , Aravind Gopalakrishnan , Jun Nakajima List-Id: xen-devel@lists.xenproject.org On 23/09/14 21:17, Boris Ostrovsky wrote: > On 09/23/2014 02:23 PM, Andrew Cooper wrote: >> On 23/09/14 19:20, Boris Ostrovsky wrote: >>> On 09/23/2014 12:09 PM, Andrew Cooper wrote: >>>> Analysis of XSAs 105 and 106 show that is possible to force a race >>>> condition >>>> which causes any arbitrary instruction to be emulated. >>>> >>>> To aid testing, explicitly introduce the Forced Emulation Prefix for >>>> debug >>>> builds alone. >>>> >>>> Signed-off-by: Andrew Cooper >>>> CC: Keir Fraser >>>> CC: Jan Beulich >>>> CC: Boris Ostrovsky >>>> CC: Suravee Suthikulpanit >>>> CC: Aravind Gopalakrishnan >>>> CC: Jun Nakajima >>>> CC: Eddie Dong >>>> CC: Kevin Tian >>>> >>>> --- >>>> v2: (all suggested by Jan) >>>> * Use hvm_fetch_from_guest_virt_nofault() in preference to >>>> copy_from_guest() >>>> * Vastly reduce use of #ifndef NDEBUG >>>> --- >>>> docs/misc/xen-command-line.markdown | 11 +++++++++++ >>>> xen/arch/x86/hvm/hvm.c | 5 +++++ >>>> xen/arch/x86/hvm/svm/svm.c | 13 +++++++++++++ >>>> xen/arch/x86/hvm/vmx/vmx.c | 13 +++++++++++++ >>>> xen/include/asm-x86/hvm/hvm.h | 7 +++++++ >>>> 5 files changed, 49 insertions(+) >>>> >>>> diff --git a/docs/misc/xen-command-line.markdown >>>> b/docs/misc/xen-command-line.markdown >>>> index af93e17..389701a 100644 >>>> --- a/docs/misc/xen-command-line.markdown >>>> +++ b/docs/misc/xen-command-line.markdown >>>> @@ -682,6 +682,17 @@ Bit 11 - MSR operation logging >>>> Recognized in debug builds of the hypervisor only. >>>> +### hvm\_fep >>>> +> `= ` >>>> + >>>> +> Default: `false` >>>> + >>>> +Allow use of the Forced Emulation Prefix in HVM guests, to allow >>>> emulation of >>>> +arbitrary instructions. >>>> + >>>> +This option is intended for development purposes, and is only >>>> available in >>>> +debug builds of the hypervisor. >>>> + >>>> ### hvm\_port80 >>>> > `= ` >>>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c >>>> index 5c7e0a4..34f28d0 100644 >>>> --- a/xen/arch/x86/hvm/hvm.c >>>> +++ b/xen/arch/x86/hvm/hvm.c >>>> @@ -86,6 +86,11 @@ unsigned long __attribute__ ((__section__ >>>> (".bss.page_aligned"))) >>>> static bool_t __initdata opt_hap_enabled = 1; >>>> boolean_param("hap", opt_hap_enabled); >>>> +#ifndef opt_hvm_fep >>>> +bool_t opt_hvm_fep; >>>> +boolean_param("hvm_fep", opt_hvm_fep); >>>> +#endif >>>> + >>>> static int cpu_callback( >>>> struct notifier_block *nfb, unsigned long action, void *hcpu) >>>> { >>>> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c >>>> index b6beefc..cda968b 100644 >>>> --- a/xen/arch/x86/hvm/svm/svm.c >>>> +++ b/xen/arch/x86/hvm/svm/svm.c >>>> @@ -2118,6 +2118,19 @@ static void svm_vmexit_ud_intercept(struct >>>> cpu_user_regs *regs) >>>> struct hvm_emulate_ctxt ctxt; >>>> int rc; >>>> + if ( opt_hvm_fep ) >>>> + { >>>> + char sig[5]; /* ud2; .ascii "xen" */ >>>> + >>>> + if ( (hvm_fetch_from_guest_virt_nofault( >>>> + sig, regs->eip, sizeof(sig), 0) == HVMCOPY_okay) && >>>> + (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) ) >>>> + { >>>> + regs->eip += sizeof(sig); >>>> + regs->eflags &= ~X86_EFLAGS_RF; >>>> + } >>>> + } >>> This code is exactly the same for SVM and VMX. Can it be factored out? >>> >>> -boris >> It can, and I considered that, but it would prevent optimising to >> nothing for non-debug builds. Given that it was a single simple if() >> statement, I chose not to. > > What about an inline (or a macro)? It won't help with code size but is > a good thing from code maintainability point of vew. > > -boris > I have vehement dislike of macros for things like this, where a static inline should be used. When attempting to make a static inline, the use of in include/asm-x86/hvm.h (which is the only logical place for it IMO) causes a failure to compile due to include dependency issues, and an incomplete type definitions of struct domain and vcpu. I currently lack enough TUITs to investigate. ~Andrew