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.
