linux-kernel - [RFC PATCH v4 1/8] KVM:VMX: Define CET VMCS fields and bits

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Date:   Mon, 18 Mar 2019 23:03:44 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, kvm@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, yu-cheng.yu@...el.com
Cc:     Yang Weijiang <weijiang.yang@...el.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: [RFC PATCH v4 1/8] KVM:VMX: Define CET VMCS fields and bits

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_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_TABLE : 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_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_TABLE : 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..fd70c4577c5a 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_S_CET                     = 0x00006828,
+	GUEST_SSP                       = 0x0000682a,
+	GUEST_INTR_SSP_TABLE            = 0x0000682c,
 	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_S_CET                      = 0x00006c18,
+	HOST_SSP                        = 0x00006c1a,
+	HOST_INTR_SSP_TABLE             = 0x00006c1c
 };
 
 /*
-- 
2.17.1