linux-kernel - Re: [PATCH v9 23/27] KVM: VMX: Set host constant supervisor states to VMCS fields

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Date: Fri, 26 Jan 2024 17:37:19 +0800
From: "Yang, Weijiang" <weijiang.yang@...el.com>
To: Chao Gao <chao.gao@...el.com>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>, <dave.hansen@...el.com>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<yuan.yao@...ux.intel.com>, <peterz@...radead.org>,
	<rick.p.edgecombe@...el.com>, <mlevitsk@...hat.com>, <john.allen@....com>
Subject: Re: [PATCH v9 23/27] KVM: VMX: Set host constant supervisor states to
 VMCS fields

On 1/26/2024 2:31 PM, Chao Gao wrote:
> On Tue, Jan 23, 2024 at 06:41:56PM -0800, Yang Weijiang wrote:
>> Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly.
>> Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after
>> post-boot(The exception is BIOS call case but vCPU thread never across it)
>> and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/
>> VM-Exit sequence.
>>
>> Host supervisor shadow stack is not enabled now and SSP is not accessible
>> to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field
>> to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP
>> before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/
>> SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc.
>>
>> Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set
>> in MSR_IA32_S_CET as KVM cannot co-exit with it correctly.
>>
>> Suggested-by: Sean Christopherson <seanjc@...gle.com>
>> Suggested-by: Chao Gao <chao.gao@...el.com>
>> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
>> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Reviewed-by: Chao Gao <chao.gao@...el.com>
>
> two nits below.
>
>> ---
>> arch/x86/kvm/vmx/capabilities.h |  4 ++++
>> arch/x86/kvm/vmx/vmx.c          | 15 +++++++++++++++
>> arch/x86/kvm/x86.c              | 14 ++++++++++++++
>> arch/x86/kvm/x86.h              |  1 +
>> 4 files changed, 34 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
>> index 41a4533f9989..ee8938818c8a 100644
>> --- a/arch/x86/kvm/vmx/capabilities.h
>> +++ b/arch/x86/kvm/vmx/capabilities.h
>> @@ -106,6 +106,10 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
>> 	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
>> }
>>
>> +static inline bool cpu_has_load_cet_ctrl(void)
> s/cet_ctrl/cet_state
>
>> +{
>> +	return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_CET_STATE);
> nit: unnecessary brackets.

OK, will fix these nits.