On Mon, Mar 18, 2019 at 11:03:44PM +0800, Yang Weijiang wrote:
> CET - Control-flow Enforcement Technology, it's used to
> protect against return/jump oriented programming (ROP)
> attacks. It provides the following capabilities to defend
> against ROP/JOP style control-flow subversion attacks:
> - Shadow Stack (SHSTK):
> A second stack for the program that is
> used exclusively for control transfer
> operations.
> - Indirect Branch Tracking (IBT):
> Free branch protection to defend against
> Jump/Call Oriented Programming.
>
> On processors that support CET, VMX saves/restores
> the states of IA32_S_CET, SSP and IA32_INTR_SSP_TABL_ADDR MSR
^^^^
Please spell out "table" in full, here and below.
> to the VMCS area for Guest/Host unconditionally.
>
> If VM_EXIT_LOAD_HOST_CET_STATE = 1, the host CET MSRs are
> restored from VMCS host-state area at VM exit as follows:
This contradicts the above statement that "VMX saves/restores ...
IA32_S_CET, SSP and IA32_INTR_SSP_TABL_ADDR MSR" unconditionally.
>
> - HOST_S_CET: Host supervisor mode IA32_S_CET MSR is loaded
> from this field.
Maybe provide a brief introduction on the MSRs instead of mixing that
in with the VMCS field definition? "Host supervisor mode IA32_S_CET"
makes it sound as if the MSR only exists at cpl=0 or something.
>
> - HOST_SSP : Host SSP is loaded from this field.
>
> - HOST_INTR_SSP_TABLE : Host IA32_INTR_SSP_TABL_ADDR
^^^^
> MSR is loaded from this field.
>
> If VM_ENTRY_LOAD_GUEST_CET_STATE = 1, the guest CET MSRs are loaded
> from VMCS guest-state area at VM entry as follows:
>
> - GUEST_S_CET : Guest supervisor mode IA32_S_CET MSR is loaded
> from this field.
>
> - GUEST_SSP : Guest SSP is loaded from this field.
>
> - GUEST_INTR_SSP_TABLE : Guest IA32_INTR_SSP_TABL_ADDR
^^^^
> MSR is loaded from this field.
You can probably drop the per-field descriptions, the intro regarding
VM_EXIT_LOAD_{HOST,GUEST}_CET_STATE should make it obvious to readers
that these fields contain host/guest values, and the names line up with
the MSRs (assuming you add a brief intro on the MSRs). E.g.:
If VM_EXIT_LOAD_HOST_CET_STATE = 1, the host's CET MSRs are restored
from the following VMCS fields at VM-Exit:
- HOST_S_CET
- HOST_SSP
- HOST_INTR_SSP_TABLE
>
> Additionally, to context switch guest and host CET states, the VMM
> uses xsaves/xrstors instructions to save/restore the guest CET states
> at VM exit/entry. The CET xsave area is within thread_struct.fpu area.
> If OS execution flow changes during task switch/interrupt/exception etc.,
> the OS also relies on xsaves/xrstors to switch CET states accordingly.
>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Assuming you both worked on these patches, a Co-developed-by: tag is
needed for Zhang Yi. The current docs on Co-developed-by: are a bit
sparse, linux-next has a patch with more information on its usage[1].
https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/+/24a2bb90741bf86ddcf6558be419e182ff44fc95
> 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 ade0f153947d..fd70c4577c5a 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -98,6 +98,7 @@
> #define VM_EXIT_LOAD_IA32_EFER 0x00200000
> #define VM_EXIT_SAVE_VMX_PREEMPTION_TIMER 0x00400000
> #define VM_EXIT_CLEAR_BNDCFGS 0x00800000
> +#define VM_EXIT_LOAD_HOST_CET_STATE 0x10000000
>
> #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR 0x00036dff
>
> @@ -109,6 +110,7 @@
> #define VM_ENTRY_LOAD_IA32_PAT 0x00004000
> #define VM_ENTRY_LOAD_IA32_EFER 0x00008000
> #define VM_ENTRY_LOAD_BNDCFGS 0x00010000
> +#define VM_ENTRY_LOAD_GUEST_CET_STATE 0x00100000
>
> #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR 0x000011ff
>
> @@ -325,6 +327,9 @@ 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,
> @@ -337,6 +342,9 @@ 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
> };
>
> /*
> --
> 2.17.1
>
