linux-kernel - Re: [PATCH v15 21/41] KVM: nVMX: Prepare for enabling CET support for nested guest

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <26947f1a-2162-4083-b39f-c360d6046877@zytor.com>
Date: Wed, 17 Sep 2025 21:48:10 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Mathias Krause <minipli@...ecurity.net>,
        John Allen <john.allen@....com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Chao Gao <chao.gao@...el.com>, Maxim Levitsky <mlevitsk@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v15 21/41] KVM: nVMX: Prepare for enabling CET support for
 nested guest

On 9/12/2025 4:22 PM, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
> index 56fd150a6f24..4ad6b16525b9 100644
> --- a/arch/x86/kvm/vmx/vmcs12.h
> +++ b/arch/x86/kvm/vmx/vmcs12.h
> @@ -117,7 +117,13 @@ struct __packed vmcs12 {
>   	natural_width host_ia32_sysenter_eip;
>   	natural_width host_rsp;
>   	natural_width host_rip;
> -	natural_width paddingl[8]; /* room for future expansion */
> +	natural_width host_s_cet;
> +	natural_width host_ssp;
> +	natural_width host_ssp_tbl;
> +	natural_width guest_s_cet;
> +	natural_width guest_ssp;
> +	natural_width guest_ssp_tbl;
> +	natural_width paddingl[2]; /* room for future expansion */
>   	u32 pin_based_vm_exec_control;
>   	u32 cpu_based_vm_exec_control;
>   	u32 exception_bitmap;
> @@ -294,6 +300,12 @@ static inline void vmx_check_vmcs12_offsets(void)
>   	CHECK_OFFSET(host_ia32_sysenter_eip, 656);
>   	CHECK_OFFSET(host_rsp, 664);
>   	CHECK_OFFSET(host_rip, 672);
> +	CHECK_OFFSET(host_s_cet, 680);
> +	CHECK_OFFSET(host_ssp, 688);
> +	CHECK_OFFSET(host_ssp_tbl, 696);
> +	CHECK_OFFSET(guest_s_cet, 704);
> +	CHECK_OFFSET(guest_ssp, 712);
> +	CHECK_OFFSET(guest_ssp_tbl, 720);
>   	CHECK_OFFSET(pin_based_vm_exec_control, 744);
>   	CHECK_OFFSET(cpu_based_vm_exec_control, 748);
>   	CHECK_OFFSET(exception_bitmap, 752);


This patch modifies struct vms12 without updating the corresponding vmcs12
definition in Documentation/virt/kvm/x86/nested-vmx.rst.  However,
duplicating the definition within the same source tree seems unnecessary
and prone to inconsistencies.  E.g., the following fields are missing in
Documentation/virt/kvm/x86/nested-vmx.rst:

	...
	u64 posted_intr_desc_addr;
	...
	u64 eoi_exit_bitmap0;
	u64 eoi_exit_bitmap1;
	u64 eoi_exit_bitmap2;
	u64 eoi_exit_bitmap3;
	u64 xss_exit_bitmap;
	...

What's more, the 64-bit padding fields are completely messed up; we have
used 9 u64 after host_ia32_efer:

         u64 host_ia32_perf_global_ctrl;
         u64 vmread_bitmap;
         u64 vmwrite_bitmap;
         u64 vm_function_control;
         u64 eptp_list_address;
         u64 pml_address;
         u64 encls_exiting_bitmap;
         u64 tsc_multiplier;
         u64 padding64[1]; /* room for future expansion */


But it's 8 u64 after host_ia32_efer in the documentation:

	u64 padding64[8]; /* room for future expansion */


We probably should remove it from Documentation/virt/kvm/x86/nested-vmx.rst
and instead add a reference to arch/x86/kvm/vmx/vmcs12.h.