[PATCH v14 04/13] KVM: VMX: Introduce CET VMCS fields and flags

Yang Weijiang
2020-11-06T01:07:20Z

CET (Control-flow Enforcement Technology) is a CPU feature used to prevent
Return/Jump-Oriented Programming (ROP/JOP) attacks. CET introduces a new
exception type, Control Protection (#CP), and two sub-features to defend
against ROP/JOP style control-flow subversion attacks:

Shadow Stack (SHSTK):
A shadow stack is a second stack used exclusively for control transfer
operations. The shadow stack is separate from the data/normal stack and
can be enabled individually in user and kernel mode. When shadow stacks
are enabled, CALL pushes the return address on both the data and shadow
stack. RET pops the return address from both stacks and compares them.
If the return addresses from the two stacks do not match, the processor
signals a #CP.

Indirect Branch Tracking (IBT):
IBT adds a new instrution, ENDBRANCH, that is used to mark valid target
addresses of indirect branches (CALL, JMP, ENCLU[EEXIT], etc...). If an
indirect branch is executed and the next instruction is _not_ an
ENDBRANCH, the processor signals a #CP.

Several new CET MSRs are defined to support CET:
MSR_IA32_{U,S}_CET: Controls the CET settings for user mode and kernel
mode respectively.

MSR_IA32_PL{0,1,2,3}_SSP: Stores shadow stack pointers for CPL-0,1,2,3
protection respectively.

MSR_IA32_INT_SSP_TAB: Stores base address of shadow stack pointer table.

Two XSAVES state bits are introduced for CET:
IA32_XSS:[bit 11]: Control saving/restoring user mode CET states
IA32_XSS:[bit 12]: Control saving/restoring kernel mode CET states.

Six VMCS fields are introduced for CET:
{HOST,GUEST}_S_CET: Stores CET settings for kernel mode.
{HOST,GUEST}_SSP: Stores shadow stack pointer of current task/thread.
{HOST,GUEST}_INTR_SSP_TABLE: Stores base address of shadow stack pointer
table.

If VM_EXIT_LOAD_HOST_CET_STATE = 1, the host CET states are restored from
the following VMCS fields at VM-Exit:
HOST_S_CET
HOST_SSP
HOST_INTR_SSP_TABLE

If VM_ENTRY_LOAD_GUEST_CET_STATE = 1, the guest CET states are loaded from
the following VMCS fields at VM-Entry:
GUEST_S_CET
GUEST_SSP
GUEST_INTR_SSP_TABLE

Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.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 f8ba5289ecb0..2b1c55f32d5b 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -94,6 +94,7 @@
#define VM_EXIT_CLEAR_BNDCFGS 0x00800000
#define VM_EXIT_PT_CONCEAL_PIP 0x01000000
#define VM_EXIT_CLEAR_IA32_RTIT_CTL 0x02000000
+#define VM_EXIT_LOAD_CET_STATE 0x10000000

#define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR 0x00036dff

@@ -107,6 +108,7 @@
#define VM_ENTRY_LOAD_BNDCFGS 0x00010000
#define VM_ENTRY_PT_CONCEAL_PIP 0x00020000
#define VM_ENTRY_LOAD_IA32_RTIT_CTL 0x00040000
+#define VM_ENTRY_LOAD_CET_STATE 0x00100000

#define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR 0x000011ff

@@ -328,6 +330,9 @@ 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,
@@ -340,6 +345,9 @@ 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
};

/*
--
2.17.2