linux-kernel - Re: [PATCH v3 1/8] KVM:VMX: Define CET VMCS fields and bits

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Date:   Tue, 26 Feb 2019 11:31:11 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, yu-cheng.yu@...el.com,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v3 1/8] KVM:VMX: Define CET VMCS fields and bits

On Mon, Feb 25, 2019 at 10:32 PM Yang Weijiang <weijiang.yang@...el.com> wrote:
>
> CET - Control-flow Enforcement Technology, it's used to
> protect against return/jump oriented programming (ROP)
> attacks. It provides the following capabilities to defend
> against ROP/JOP style control-flow subversion attacks:
> - Shadow Stack (SHSTK):
>                  A second stack for the program that is
>                  used exclusively for control transfer
>                  operations.
> - Indirect Branch Tracking (IBT):
>                  Free branch protection to defend against
>                  Jump/Call Oriented Programming.
>
> On processors that support CET, VMX saves/restores
> the states of IA32_S_CET, SSP and IA32_INTR_SSP_TABL_ADDR MSR
> to the VMCS area for Guest/Host unconditionally.
>
> If VM_EXIT_LOAD_HOST_CET_STATE = 1, the host CET MSRs are
> restored from VMCS host-state area at VM exit as follows:
>
> - HOST_IA32_S_CET: Host supervisor mode IA32_S_CET MSR is loaded
>                    from this field.
>
> - HOST_SSP :       Host SSP is loaded from this field.
>
> - HOST_INTR_SSP_TABL_ADDR : Host IA32_INTR_SSP_TABL_ADDR
>                              MSR is loaded from this field.
>
> If VM_ENTRY_LOAD_GUEST_CET_STATE = 1, the guest CET MSRs are loaded
> from VMCS guest-state area at VM entry as follows:
>
> - GUEST_IA32_S_CET : Guest supervisor mode IA32_S_CET MSR is loaded
>                      from this field.
>
> - GUEST_SSP :        Guest SSP is loaded from this field.
>
> - GUEST_INTR_SSP_TABL_ADDR : Guest IA32_INTR_SSP_TABL_ADDR
>                              MSR is loaded from this field.
>
> Additionally, to context switch guest and host CET states, the VMM
> uses xsaves/xrstors instructions to save/restore the guest CET states
> at VM exit/entry. The CET xsave area is within thread_struct.fpu area.
> If OS execution flow changes during task switch/interrupt/exception etc.,
> the OS also relies on xsaves/xrstors to switch CET states accordingly.
>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/include/asm/vmx.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index ade0f153947d..395c1f7e5938 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -98,6 +98,7 @@
>  #define VM_EXIT_LOAD_IA32_EFER                  0x00200000
>  #define VM_EXIT_SAVE_VMX_PREEMPTION_TIMER       0x00400000
>  #define VM_EXIT_CLEAR_BNDCFGS                   0x00800000
> +#define VM_EXIT_LOAD_HOST_CET_STATE             0x10000000
>
>  #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR      0x00036dff
>
> @@ -109,6 +110,7 @@
>  #define VM_ENTRY_LOAD_IA32_PAT                 0x00004000
>  #define VM_ENTRY_LOAD_IA32_EFER                 0x00008000
>  #define VM_ENTRY_LOAD_BNDCFGS                   0x00010000
> +#define VM_ENTRY_LOAD_GUEST_CET_STATE           0x00100000
>
>  #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR     0x000011ff
>
> @@ -325,6 +327,9 @@ enum vmcs_field {
>         GUEST_PENDING_DBG_EXCEPTIONS    = 0x00006822,
>         GUEST_SYSENTER_ESP              = 0x00006824,
>         GUEST_SYSENTER_EIP              = 0x00006826,
> +       GUEST_IA32_S_CET                = 0x00006828,
> +       GUEST_SSP                       = 0x0000682a,
> +       GUEST_INTR_SSP_TABL_ADDR        = 0x0000682c,

Nit: TABL is an unusual abbreviation. Perhaps TBL here and below? And
why did you drop the 'IA32' here, but not in GUEST_IA32_S_CET above?
(It is true that there seems to be no rhyme or reason to the mnemonics
chosen here. For example, EFER keeps its IA32, but SYSENTER_EIP
doesn't. Sigh.)

>         HOST_CR0                        = 0x00006c00,
>         HOST_CR3                        = 0x00006c02,
>         HOST_CR4                        = 0x00006c04,
> @@ -337,6 +342,9 @@ enum vmcs_field {
>         HOST_IA32_SYSENTER_EIP          = 0x00006c12,
>         HOST_RSP                        = 0x00006c14,
>         HOST_RIP                        = 0x00006c16,
> +       HOST_IA32_S_CET                 = 0x00006c18,
> +       HOST_SSP                        = 0x00006c1a,
> +       HOST_INTR_SSP_TABL_ADDR         = 0x00006c1c
>  };
>
>  /*
> --
> 2.17.1

Reviewed-by: Jim Mattson <jmattson@...gle.com>