[edk2-devel] [PATCH v3 1/3] OvmfPkg/MemEncryptHypercallLib: add library to support SEV hypercalls.
Dov Murik
dovmurik at linux.vnet.ibm.com
Sun Dec 6 12:43:45 UTC 2020
On 04/12/2020 2:03, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra at amd.com>
>
> Add SEV and SEV-ES hypercall abstraction library to support SEV Page
> encryption/deceryption status hypercalls for SEV and SEV-ES guests.
>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
>
> Signed-off-by: Ashish Kalra <ashish.kalra at amd.com>
> ---
> OvmfPkg/Include/Library/MemEncryptHypercallLib.h | 37 +++++++
> OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.c | 105 ++++++++++++++++++++
> OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf | 39 ++++++++
> OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm | 39 ++++++++
> OvmfPkg/OvmfPkgX64.dsc | 1 +
> 5 files changed, 221 insertions(+)
>
> diff --git a/OvmfPkg/Include/Library/MemEncryptHypercallLib.h b/OvmfPkg/Include/Library/MemEncryptHypercallLib.h
> new file mode 100644
> index 0000000000..cd46a7f2b3
> --- /dev/null
> +++ b/OvmfPkg/Include/Library/MemEncryptHypercallLib.h
> @@ -0,0 +1,37 @@
> +/** @file
> +
> + Define Secure Encrypted Virtualization (SEV) hypercall library.
> +
> + Copyright (c) 2020, AMD Incorporated. All rights reserved.<BR>
> +
> + SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#ifndef _MEM_ENCRYPT_HYPERCALL_LIB_H_
> +#define _MEM_ENCRYPT_HYPERCALL_LIB_H_
> +
> +#include <Base.h>
> +
> +#define SEV_PAGE_ENC_HYPERCALL 12
> +
> +/**
> + This hyercall is used to notify hypervisor when a page is marked as
> + 'decrypted' (i.e C-bit removed).
> +
> + @param[in] PhysicalAddress The physical address that is the start address
> + of a memory region.
> + @param[in] Length The length of memory region
> + @param[in] Mode SetCBit or ClearCBit
> +
> +**/
> +
> +VOID
> +EFIAPI
> +SetMemoryEncDecHypercall3 (
> + IN UINTN PhysicalAddress,
> + IN UINTN Length,
> + IN UINTN Mode
> + );
(1) I'm not sure why the "3" is needed at the end of the function name.
(2) The second argument is called 'Length' here and 'Pages' in the .c
file. Which name is correct? If the semantics of the hypercall deals
only with whole pages, maybe it'll be better to modify the address to
GFN and length to NumberOfPages. This way you don't have to do deal
with non-page-aligned addresses or lengths. Of course this may reflect
on changes needed in the hypercall implementation itself in KVM.
(3) Mode: is this actually a boolean, or the enum which can be
SetCBit(=0) or ClearCBit(=1)? Maybe a clearer argument would be "BOOL
Encrypted" or "BOOL NewCBitValue"? Of course this has to match
semantics of this argument in KVM.
> +
> +#endif
> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.c b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.c
> new file mode 100644
> index 0000000000..f1136b7d36
> --- /dev/null
> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.c
> @@ -0,0 +1,105 @@
> +/** @file
> +
> + Secure Encrypted Virtualization (SEV) hypercall helper library
> +
> + Copyright (c) 2020, AMD Incorporated. All rights reserved.<BR>
> +
> + SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#include <Uefi.h>
> +#include <Uefi/UefiBaseType.h>
> +#include <Library/BaseLib.h>
> +#include <Library/DebugLib.h>
> +#include <Library/VmgExitLib.h>
> +#include <Register/Amd/Ghcb.h>
> +#include <Register/Amd/Msr.h>
> +#include <Library/MemEncryptSevLib.h>
> +#include <Library/MemEncryptHypercallLib.h>
> +
> +//
> +// Interface exposed by the ASM implementation of the core hypercall
> +//
> +//
> +
> +VOID
> +EFIAPI
> +SetMemoryEncDecHypercall3AsmStub (
> + IN UINTN HypercallNum,
> + IN UINTN PhysicalAddress,
> + IN UINTN Length,
> + IN UINTN Mode
> + );
> +
> +/**
> + This function returns the current CPU privilege level, implemented
> + in ASM helper stub.
> +
> +**/
> +
> +UINT8
> +EFIAPI
> +GetCurrentCpuPrivilegeLevel (
> + VOID
> + );
> +
> +STATIC
> +VOID
> +GhcbSetRegValid (
> + IN OUT GHCB *Ghcb,
> + IN GHCB_REGISTER Reg
> + )
> +{
> + UINT32 RegIndex;
> + UINT32 RegBit;
> +
> + RegIndex = Reg / 8;
> + RegBit = Reg & 0x07;
> +
> + Ghcb->SaveArea.ValidBitmap[RegIndex] |= (1 << RegBit);
> +}
> +
> +VOID
> +EFIAPI
> +SetMemoryEncDecHypercall3 (
> + IN PHYSICAL_ADDRESS PhysicalAddress,
> + IN UINTN Pages,
> + IN UINTN Mode
> + )
> +{
> + if (MemEncryptSevEsIsEnabled ()) {
> + MSR_SEV_ES_GHCB_REGISTER Msr;
> + GHCB *Ghcb;
> + BOOLEAN InterruptState;
> + UINT64 Status;
> +
> + Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
> + Ghcb = Msr.Ghcb;
> +
> + VmgInit (Ghcb, &InterruptState);
> +
> + Ghcb->SaveArea.Rax = SEV_PAGE_ENC_HYPERCALL;
> + GhcbSetRegValid (Ghcb, GhcbRax);
> + Ghcb->SaveArea.Rbx = PhysicalAddress;
> + GhcbSetRegValid (Ghcb, GhcbRbx);
> + Ghcb->SaveArea.Rcx = Pages;
> + GhcbSetRegValid (Ghcb, GhcbRcx);
> + Ghcb->SaveArea.Rdx = Mode;
> + GhcbSetRegValid (Ghcb, GhcbRdx);
> + Ghcb->SaveArea.Cpl = GetCurrentCpuPrivilegeLevel();
> + GhcbSetRegValid (Ghcb, GhcbCpl);
> +
> + Status = VmgExit (Ghcb, SVM_EXIT_VMMCALL, 0, 0);
> + if (Status) {
> + DEBUG ((DEBUG_ERROR, "SVM_EXIT_VMMCALL failed %lx\n", Status));
> + }
> + VmgDone (Ghcb, InterruptState);
> + } else {
> + SetMemoryEncDecHypercall3AsmStub (
> + SEV_PAGE_ENC_HYPERCALL,
> + PhysicalAddress,
> + Pages,
> + Mode);
> + }
> +}
> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
> new file mode 100644
> index 0000000000..1936fe5b37
> --- /dev/null
> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
> @@ -0,0 +1,39 @@
> +## @file
> +# Library provides the hypervisor helper functions for SEV guest
> +#
> +# Copyright (c) 2020 Advanced Micro Devices. All rights reserved.<BR>
> +#
> +# SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#
> +##
> +
> +[Defines]
> + INF_VERSION = 1.25
> + BASE_NAME = MemEncryptHypercallLib
> + FILE_GUID = 86f2501e-f128-45f3-91c4-3cff31656ca8
> + MODULE_TYPE = BASE
> + VERSION_STRING = 1.0
> + LIBRARY_CLASS = MemEncryptHypercallLib|SEC PEI_CORE PEIM DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_DRIVER
> +
> +#
> +# The following information is for reference only and not required by the build
> +# tools.
> +#
> +# VALID_ARCHITECTURES = IA32 X64
> +#
> +
> +[Packages]
> + MdeModulePkg/MdeModulePkg.dec
> + MdePkg/MdePkg.dec
> + UefiCpuPkg/UefiCpuPkg.dec
> + OvmfPkg/OvmfPkg.dec
> +
> +[Sources.X64]
> + MemEncryptHypercallLib.c
> + X64/AsmHelperStub.nasm
> +
> +[LibraryClasses]
> + BaseLib
> + DebugLib
> + VmgExitLib
> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm b/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm
> new file mode 100644
> index 0000000000..5d8a7aa85a
> --- /dev/null
> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm
> @@ -0,0 +1,39 @@
> +DEFAULT REL
> +SECTION .text
> +
> +; VOID
> +; EFIAPI
> +; SetMemoryEncDecHypercall3AsmStub (
> +; IN UINT HypercallNum,
> +; IN INTN Arg1,
> +; IN INTN Arg2,
> +; IN INTN Arg3
> +; );
The name of the function hints that this has something to do with memory
enc/dec, but actually this is a generic vmmcall-based hypercall. In
your corresponding linux patch
<https://lore.kernel.org/kvm/b6bc54ed6c8ae4444f3acf1ed4386010783ad386.1606782580.git.ashish.kalra@amd.com/>
you called it kvm_sev_hypercall3, so I assume something like that would
be good here too. Also, to support future hypercalls, allow it to
return an INTN (value of rax), even though that is not used for the
current hypercall in question.
> +global ASM_PFX(SetMemoryEncDecHypercall3AsmStub)
> +ASM_PFX(SetMemoryEncDecHypercall3AsmStub):
> + ; UEFI calling conventions require RBX to
> + ; be nonvolatile/callee-saved.
> + push rbx
> + ; Copy HypercallNumber to rax
> + mov rax, rcx
> + ; Copy Arg1 to the register expected by KVM
> + mov rbx, rdx
> + ; Copy Arg2 to register expected by KVM
> + mov rcx, r8
> + ; Copy Arg2 to register expected by KVM
> + mov rdx, r9
> + ; Call VMMCALL
> + vmmcall
> + pop rbx
> + ret
> +
> +; UINT8
> +; EFIAPI
> +; GetCurrentCpuPrivilegeLevel (
> +; VOID
> +; );
> +global ASM_PFX(GetCurrentCpuPrivilegeLevel)
> +ASM_PFX(GetCurrentCpuPrivilegeLevel):
> + mov ax, cs
> + and al, 0x3
> + ret
I think GetCurrentCpuPrivilegeLevel can be implemented in C as:
return AsmReadCS() & 0x3;
> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
> index e59ae05b73..97c31c7586 100644
> --- a/OvmfPkg/OvmfPkgX64.dsc
> +++ b/OvmfPkg/OvmfPkgX64.dsc
> @@ -174,6 +174,7 @@
> VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
> LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
> MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
> + MemEncryptHypercallLib|OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
> !if $(SMM_REQUIRE) == FALSE
> LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
> !endif
>
-Dov
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