linux-kernel - Re: [RFC 02/10] x86/kvm: Add IBPB support

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Date:   Sat, 20 Jan 2018 12:28:37 -0800 (PST)
From:   Liran Alon <liran.alon@...cle.com>
To:     <karahmed@...zon.de>
Cc:     <labbott@...hat.com>, <luto@...nel.org>,
        <Janakarajan.Natarajan@....com>, <bp@...e.de>,
        <torvalds@...ux-foundation.org>, <asit.k.mallick@...el.com>,
        <rkrcmar@...hat.com>, <dave.hansen@...el.com>, <hpa@...or.com>,
        <mingo@...hat.com>, <jun.nakajima@...el.com>, <x86@...nel.org>,
        <dwmw@...zon.co.uk>, <ashok.raj@...el.com>,
        <arjan.van.de.ven@...el.com>, <tim.c.chen@...ux.intel.com>,
        <pbonzini@...hat.com>, <linux-kernel@...r.kernel.org>,
        <ak@...ux.intel.com>, <peterz@...radead.org>, <tglx@...utronix.de>,
        <gregkh@...uxfoundation.org>, <mhiramat@...nel.org>,
        <arjan@...ux.intel.com>, <thomas.lendacky@....com>,
        <dan.j.williams@...el.com>, <joro@...tes.org>,
        <kvm@...r.kernel.org>, <aarcange@...hat.com>
Subject: Re: [RFC 02/10] x86/kvm: Add IBPB support


----- karahmed@...zon.de wrote:

> From: Ashok Raj <ashok.raj@...el.com>
> 
> Add MSR passthrough for MSR_IA32_PRED_CMD and place branch predictor
> barriers on switching between VMs to avoid inter VM specte-v2
> attacks.
> 
> [peterz: rebase and changelog rewrite]
> [dwmw2: fixes]
> [karahmed: - vmx: expose PRED_CMD whenever it is available
> 	   - svm: only pass through IBPB if it is available]
> 
> Cc: Asit Mallick <asit.k.mallick@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Arjan Van De Ven <arjan.van.de.ven@...el.com>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Jun Nakajima <jun.nakajima@...el.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link:
> https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_1515720739-2D43819-2D6-2Dgit-2Dsend-2Demail-2Dashok.raj-40intel.com&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=0Y6G18aD_Uxu0jx8J4AbITM-rlF_AyH591Zg5HwA5L8&s=uf8SxTOp8zu-Q5H9l-Ko-UoLUgvfuN5bvLdJwe6kUXc&e=
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  arch/x86/kvm/svm.c | 14 ++++++++++++++
>  arch/x86/kvm/vmx.c |  4 ++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2744b973..cfdb9ab 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -529,6 +529,7 @@ struct svm_cpu_data {
>  	struct kvm_ldttss_desc *tss_desc;
>  
>  	struct page *save_area;
> +	struct vmcb *current_vmcb;
>  };
>  
>  static DEFINE_PER_CPU(struct svm_cpu_data *, svm_data);
> @@ -918,6 +919,9 @@ static void svm_vcpu_init_msrpm(u32 *msrpm)
>  
>  		set_msr_interception(msrpm, direct_access_msrs[i].index, 1, 1);
>  	}
> +
> +	if (boot_cpu_has(X86_FEATURE_AMD_PRED_CMD))
> +		set_msr_interception(msrpm, MSR_IA32_PRED_CMD, 1, 1);
>  }
>  
>  static void add_msr_offset(u32 offset)
> @@ -1706,11 +1710,17 @@ static void svm_free_vcpu(struct kvm_vcpu
> *vcpu)
>  	__free_pages(virt_to_page(svm->nested.msrpm), MSRPM_ALLOC_ORDER);
>  	kvm_vcpu_uninit(vcpu);
>  	kmem_cache_free(kvm_vcpu_cache, svm);
> +	/*
> +	 * The vmcb page can be recycled, causing a false negative in
> +	 * svm_vcpu_load(). So do a full IBPB now.
> +	 */
> +	indirect_branch_prediction_barrier();
>  }
>  
>  static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
> +	struct svm_cpu_data *sd = per_cpu(svm_data, cpu);
>  	int i;
>  
>  	if (unlikely(cpu != vcpu->cpu)) {
> @@ -1739,6 +1749,10 @@ static void svm_vcpu_load(struct kvm_vcpu
> *vcpu, int cpu)
>  	if (static_cpu_has(X86_FEATURE_RDTSCP))
>  		wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
>  
> +	if (sd->current_vmcb != svm->vmcb) {
> +		sd->current_vmcb = svm->vmcb;
> +		indirect_branch_prediction_barrier();
> +	}
>  	avic_vcpu_load(vcpu, cpu);
>  }
>  
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d1e25db..3b64de2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2279,6 +2279,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu,
> int cpu)
>  	if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
>  		per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
>  		vmcs_load(vmx->loaded_vmcs->vmcs);
> +		indirect_branch_prediction_barrier();
>  	}
>  
>  	if (!already_loaded) {
> @@ -6791,6 +6792,9 @@ static __init int hardware_setup(void)
>  		kvm_tsc_scaling_ratio_frac_bits = 48;
>  	}
>  
> +	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
> +		vmx_disable_intercept_for_msr(MSR_IA32_PRED_CMD, false);
> +
>  	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
>  	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
>  	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
> -- 
> 2.7.4

Isn't it cleaner to check for "boot_cpu_has(X86_FEATURE_IBPB)" both in svm_vcpu_init_msrpm() and hardware_setup()?

-Liran