Re: [RESEND v13 02/11] KVM: VMX: Introduce CET VMCS fields and flags

[Sean Christopherson]

On Thu, Jul 16, 2020 at 11:16:18AM +0800, Yang Weijiang wrote:
> CET(Control-flow Enforcement Technology) is a CPU feature used to prevent
> Return/Jump-Oriented Programming(ROP/JOP) attacks. It provides the following
> sub-features to defend against ROP/JOP style control-flow subversion attacks:
> 
> Shadow Stack (SHSTK):
>   A second stack for program which is used exclusively for control transfer
>   operations.
> 
> Indirect Branch Tracking (IBT):
>   Code branching protection to defend against jump/call oriented programming.
> 
> Several new CET MSRs are defined in kernel 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 below
> 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 below
> VMCS fields at VM-Entry:
>   GUEST_S_CET
>   GUEST_SSP
>   GUEST_INTR_SSP_TABLE

No changes to the patch itself, but I tweaked the formatting of the changelog
a bit and expanded the introduction for SHSTK and IBT to provide a bit more
background.