Re: [PATCH v6 17/25] KVM: VMX: Introduce CET VMCS fields and control bits

[Maxim Levitsky]

On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> Control-flow Enforcement Technology (CET) is a kind of CPU feature used
> to prevent Return/CALL/Jump-Oriented Programming (ROP/COP/JOP) attacks.
> It provides two sub-features(SHSTK,IBT) to defend against ROP/COP/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 stack
>   is 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
>   generates a #CP.
> 
> Indirect Branch Tracking (IBT):
>   IBT introduces instruction(ENDBRANCH)to mark valid target addresses of
>   indirect branches (CALL, JMP etc...). If an indirect branch is executed
>   and the next instruction is _not_ an ENDBRANCH, the processor generates
>   a #CP. These instruction behaves as a NOP on platforms that have no CET.
> 
> Several new CET MSRs are defined to support CET:
>   MSR_IA32_{U,S}_CET: CET settings for {user,supervisor} CET respectively.
> 
>   MSR_IA32_PL{0,1,2,3}_SSP: SHSTK pointer linear address for CPL{0,1,2,3}.
> 
>   MSR_IA32_INT_SSP_TAB: Linear address of SHSTK pointer table, whose entry
> 			is indexed by IST of interrupt gate desc.
> 
> 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 supervisor mode CET states.
> 
> Six VMCS fields are introduced for CET:
>   {HOST,GUEST}_S_CET: Stores CET settings for kernel mode.
>   {HOST,GUEST}_SSP: Stores current active SSP.
>   {HOST,GUEST}_INTR_SSP_TABLE: Stores current active MSR_IA32_INT_SSP_TAB.
> 
> On Intel platforms, two additional bits are defined in VM_EXIT and VM_ENTRY
> control fields:
> If VM_EXIT_LOAD_CET_STATE = 1, host CET states are loaded from following
> VMCS fields at VM-Exit:
>   HOST_S_CET
>   HOST_SSP
>   HOST_INTR_SSP_TABLE
> 
> If VM_ENTRY_LOAD_CET_STATE = 1, guest CET states are loaded from following
> VMCS fields at VM-Entry:
>   GUEST_S_CET
>   GUEST_SSP
>   GUEST_INTR_SSP_TABLE
> 
> Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
>  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 0e73616b82f3..451fd4f4fedc 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -104,6 +104,7 @@
>  #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
Bit 28, matches PRM.
>  
>  #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR	0x00036dff
>  
> @@ -117,6 +118,7 @@
>  #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
Bit 20, matches PRM.


I wish we redefine these masks with BIT_ULL(n) macros for the sake of
having less chance of a mistake. Patches to refactor this are welcome!

>  
>  #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR	0x000011ff
>  
> @@ -345,6 +347,9 @@ 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,
Matches the PRM.

>  	HOST_CR0                        = 0x00006c00,
>  	HOST_CR3                        = 0x00006c02,
>  	HOST_CR4                        = 0x00006c04,
> @@ -357,6 +362,9 @@ 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
Matches the PRM as well.


Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky



>  };
>  
>  /*