| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Mon, 25 Mar 2019 08:33:04 -0700
From: Sean Christopherson <sean.j.christopherson@...el.com>
To: Xiaoyao Li <xiaoyao.li@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
chao.gao@...el.com
Subject: Re: [PATCH v3 1/2] kvm/vmx: Switch MSR_MISC_FEATURES_ENABLES between
host and guest
On Mon, Mar 25, 2019 at 04:06:49PM +0800, Xiaoyao Li wrote:
> There are two defined bits in MSR_MISC_FEATURES_ENABLES, bit 0 for cpuid
> faulting and bit 1 for ring3mwait.
>
> == cpuid Faulting ==
> cpuid faulting is a feature about CPUID instruction. When cpuid faulting
> is enabled, all execution of the CPUID instruction outside system-management
> mode (SMM) cause a general-protection (#GP) if the CPL > 0.
>
> About this feature, detailed information can be found at
> https://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf
>
> Current KVM provides software emulation of this feature for guest.
> However, because cpuid faulting takes higher priority over CPUID vm exit (Intel
> SDM vol3.25.1.1), there is a risk of leaking cpuid faulting to guest when host
> enables it. If host enables cpuid faulting by setting the bit 0 of
> MSR_MISC_FEATURES_ENABLES, it will pass to guest since there is no switch of
> MSR_MISC_FEATURES_ENABLES yet. As a result, when guest calls CPUID instruction
> in CPL > 0, it will generate a #GP instead of CPUID vm eixt.
>
> This issue will cause guest boot failure when guest uses *modprobe*
> to load modules. *modprobe* calls CPUID instruction, thus causing #GP in
> guest. Since there is no handling of cpuid faulting in #GP handler, guest
> fails boot.
>
> == ring3mwait ==
> Ring3mwait is a Xeon-Phi Product Family x200 series specific feature,
> which allows the MONITOR and MWAIT instructions to be executed in rings
> other than ring 0. The feature can be enabled by setting bit 1 in
> MSR_MISC_FEATURES_ENABLES. The register can also be read to determine
> whether the instructions are enabled at other than ring 0.
>
> About this feature, description can be found at
> https://software.intel.com/en-us/blogs/2016/10/06/intel-xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait
>
> Current kvm doesn't expose feature ring3mwait to guest. However, there is also
> a risk of leaking ring3mwait to guest if host enables it since there is no
> switch of MSR_MISC_FEATURES_ENABLES.
>
> == solution ==
> From above analysis, both cpuid faulting and ring3mwait can be leaked to guest.
> To fix this issue, MSR_MISC_FEATURES_ENABLES should be switched between host
> and guest. Since MSR_MISC_FEATURES_ENABLES is intel-specific, this patch
> implement the switching only in vmx.
>
> For the reason that kvm provides the software emulation of cpuid faulting and
> kvm doesn't expose ring3mwait to guest. MSR_MISC_FEATURES_ENABLES can be just
> cleared to zero for guest when any of the features is enabled in host.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...ux.intel.com>
> ---
> arch/x86/kernel/process.c | 1 +
> arch/x86/kvm/vmx/vmx.c | 24 ++++++++++++++++++++++++
> 2 files changed, 25 insertions(+)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 1bba1a3c0b01..94a566e79b6c 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -191,6 +191,7 @@ int set_tsc_mode(unsigned int val)
> }
>
> DEFINE_PER_CPU(u64, msr_misc_features_shadow);
> +EXPORT_PER_CPU_SYMBOL_GPL(msr_misc_features_shadow);
>
> static void set_cpuid_faulting(bool on)
> {
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 270c6566fd5a..65aa947947ba 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1031,6 +1031,16 @@ static void pt_guest_exit(struct vcpu_vmx *vmx)
> wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
> }
>
> +static void vmx_prepare_guest_misc_features_enables(struct vcpu_vmx *vmx)
No need for @vmx. My preference would be to drop the helpers entirely,
e.g. it's two lines of code, three if you count the declaration of msrval.
> +{
> + u64 msrval = this_cpu_read(msr_misc_features_shadow);
> +
> + if (!msrval)
> + return;
> +
> + wrmsrl(MSR_MISC_FEATURES_ENABLES, 0ULL);
> +}
> +
> void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -1064,6 +1074,8 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
> vmx->loaded_cpu_state = vmx->loaded_vmcs;
> host_state = &vmx->loaded_cpu_state->host_state;
>
> + vmx_prepare_guest_misc_features_enables(vmx);
> +
> /*
> * Set host fs and gs selectors. Unfortunately, 22.2.3 does not
> * allow segment selectors with cpl > 0 or ti == 1.
> @@ -1120,6 +1132,16 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
> }
> }
>
> +static void vmx_load_host_misc_features_enables(struct vcpu_vmx *vmx)
Likewise, no need for @vmx.
> +{
> + u64 msrval = this_cpu_read(msr_misc_features_shadow);
> +
> + if (!msrval)
> + return;
> +
> + wrmsrl(MSR_MISC_FEATURES_ENABLES, msrval);
> +}
> +
> static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
> {
> struct vmcs_host_state *host_state;
> @@ -1133,6 +1155,8 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
> ++vmx->vcpu.stat.host_state_reload;
> vmx->loaded_cpu_state = NULL;
>
> + vmx_load_host_misc_features_enables(vmx);
> +
> #ifdef CONFIG_X86_64
> rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
> #endif
> --
> 2.19.1
>
Powered by blists - more mailing lists