Re: [PATCH v2 11/21] KVM:VMX: Introduce CET VMCS fields and control bits

[Binbin Wu <binbin.wu@linux.intel.com>]

On 4/21/2023 9:46 PM, Yang Weijiang wrote:
> 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(SHSTK,IBT)
> 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
/s/instrution/instruction

>    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.
According to the name of the MSR, it is interrupt related, right?
It's better to describe the MSR more precisely.

>
> 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 active task/thread.
>    {HOST,GUEST}_INTR_SSP_TABLE: Stores base address of shadow stack pointer table.
ditto

>
> 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 498dc600bd5c..fe2aff27df8c 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -102,6 +102,7 @@
>   #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
>   
> @@ -115,6 +116,7 @@
>   #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
>   
> @@ -343,6 +345,9 @@ 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,
> @@ -355,6 +360,9 @@ 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
>   };
>   
>   /*