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Subject[RFC PATCH 00/62] Linux as SEV-ES Guest Support
Date
Hi,

here is the first public post of the patch-set to enable Linux to run
under SEV-ES enabled hypervisors. The code is mostly feature-complete,
but there are still a couple of bugs to fix. Nevertheless, given the
size of the patch-set, I think it is about time to ask for initial
feedback of the changes that come with it. To better understand the code
here is a quick explanation of SEV-ES first.

This patch-set does not contain the hypervisor changes necessary to run
SEV-ES enabled KVM guests. These patches will be sent separatly when
they are ready to be sent out.

What is SEV-ES
==============

SEV-ES is an acronym for 'Secure Encrypted Virtualization - Encrypted
State' and means a hardware feature of AMD processors which hides the
register state of VCPUs to the hypervisor by encrypting it. The
hypervisor can't read or make changes to the guests register state.

Most intercepts set by the hypervisor do not cause a #VMEXIT of the
guest anymore, but turn into a VMM Communication Exception (#VC
exception, vector 29) inside the guest. The error-code of this exception
is the intercept exit-code that caused the exception. The guest handles
the #VC exception by communicating with the hypervisor through a shared
data structure, the 'Guest-Hypervisor-Communication-Block' (GHCB). The
layout of that data-structure and the protocol is specified in [1].

A description of the SEV-ES hardware interface can be found in the AMD64
Architecture Programmer's Manual Volume 2, Section 15.35 [2].

Implementation Details
======================

SEV-ES guests will always boot via UEFI firmware and use the 64-bit EFI
entry point into the kernel. This implies that only 64-bit Linux x86
guests are supported.

Pre-Decompression Boot Code and Early Exception Support
-------------------------------------------------------

Intercepts that cause exceptions in the guest include instructions like
CPUID, RDMSR/WRMSR, IOIO instructions and a couple more. Some of them
are executed very early during boot, which means that exceptions need to
work that early. That is the reason big parts of this patch-set enable
support for early exceptions, first in the pre-decompression boot-code
and later also in the early boot-code of the kernel image.

As these patches add exception support to the pre-decompression boot
code, it also implements a page-fault handler to create the
identity-mapped page-table on-demand. One reason for this change is to
make use of the exception handling code in non SEV-ES guests too, so
that it is less likely to break in the future. The other reason is that
for SEV-ES guests the code needs to setup its own page-table to map the
GHCB unencrypted. Without these patches the pre-decompression code only
uses its own page-table when KASLR is enabled and used.

SIPI and INIT Handling
----------------------

The hypervisor also can't make changes to the guest register state,
which implies that it can't emulate SIPI and INIT messages. This means
that any CPU register state reset needs to be done inside the guest.
Most of this is handled in the firmware, but the Linux kernel has to
setup an AP Jump Table to boot secondary processors. CPU online/offline
handling also needs special handling, where this patch-set implements a
shortcut. An offlined CPU will not go back to real-mode when it is woken
up again, but stays in long-mode an just jumps back to the trampoline
code.

NMI Special Handling
--------------------

The last thing that needs special handling with SEV-ES are NMIs.
Hypervisors usually start to intercept IRET instructions when an NMI got
injected to find out when the NMI window is re-opened. But handling IRET
intercepts requires the hypervisor to access guest register state and is
not possible with SEV-ES. The specification under [1] solves this
problem with an NMI_COMPLETE message sent my the guest to the
hypervisor, upon which the hypervisor re-opens the NMI window for the
guest.

This patch-set sends the NMI_COMPLETE message before the actual IRET,
while the kernel is still on a valid stack and kernel cr3. This opens
the NMI-window a few instructions early, but this is fine as under
x86-64 Linux NMI-nesting is safe. The alternative would be to
single-step over the IRET, but that requires more intrusive changes to
the entry code because it does not handle entries from kernel-mode while
on the entry stack.

Besides the special handling above the patch-set contains the handlers
for the #VC exception and all the exit-codes specified in [1].

Current State of the Patches
============================

The patch-set posted here can boot an SMP Linux guest under
SEV-ES-enabled KVM and the guest survives some load-testing
(kernel-compiles). The guest boots to the graphical desktop and is
usable. But there are still know bugs and issues:

* Putting some NMI-load on the guest will make it crash usually
within a minute
* The handler for MMIO events needs more security checks when
walking the page-table
* The MMIO handler also lacks emulation for MOVS and REP MOVS
instructions like used by memcpy_toio() and memcpy_fromio().

More testing will likely uncover more bugs, but I think the patch-set is
ready for initial feedback. It grew pretty big already and handling it
becomes more and more painful.

So please review the parts of the patch-set that you find interesting
and let me know your feedback.

Thanks a lot,

Joerg

[1] https://developer.amd.com/wp-content/resources/56421.pdf
[2] https://www.amd.com/system/files/TechDocs/24593.pdf

Doug Covelli (1):
x86/vmware: Add VMware specific handling for VMMCALL under SEV-ES

Joerg Roedel (43):
KVM: SVM: Add GHCB Accessor functions
x86/traps: Move some definitions to <asm/trap_defs.h>
x86/insn-decoder: Make inat-tables.c suitable for pre-decompression
code
x86/boot/compressed: Fix debug_puthex() parameter type
x86/boot/compressed/64: Disable red-zone usage
x86/boot/compressed/64: Add IDT Infrastructure
x86/boot/compressed/64: Rename kaslr_64.c to ident_map_64.c
x86/boot/compressed/64: Add page-fault handler
x86/boot/compressed/64: Always switch to own page-table
x86/boot/compressed/64: Don't pre-map memory in KASLR code
x86/boot/compressed/64: Change add_identity_map() to take start and
end
x86/boot/compressed/64: Add stage1 #VC handler
x86/boot/compressed/64: Call set_sev_encryption_mask earlier
x86/boot/compressed/64: Check return value of
kernel_ident_mapping_init()
x86/boot/compressed/64: Add function to map a page unencrypted
x86/boot/compressed/64: Setup GHCB Based VC Exception handler
x86/fpu: Move xgetbv()/xsetbv() into separate header
x86/idt: Move IDT to data segment
x86/idt: Split idt_data setup out of set_intr_gate()
x86/head/64: Install boot GDT
x86/head/64: Reload GDT after switch to virtual addresses
x86/head/64: Load segment registers earlier
x86/head/64: Switch to initial stack earlier
x86/head/64: Load IDT earlier
x86/head/64: Move early exception dispatch to C code
x86/sev-es: Add SEV-ES Feature Detection
x86/sev-es: Compile early handler code into kernel image
x86/sev-es: Setup early #VC handler
x86/sev-es: Setup GHCB based boot #VC handler
x86/sev-es: Wire up existing #VC exit-code handlers
x86/sev-es: Handle instruction fetches from user-space
x86/sev-es: Harden runtime #VC handler for exceptions from user-space
x86/sev-es: Filter exceptions not supported from user-space
x86/sev-es: Handle RDTSCP Events
x86/sev-es: Handle #AC Events
x86/sev-es: Handle #DB Events
x86/paravirt: Allow hypervisor specific VMMCALL handling under SEV-ES
x86/realmode: Add SEV-ES specific trampoline entry point
x86/head/64: Don't call verify_cpu() on starting APs
x86/head/64: Rename start_cpu0
x86/sev-es: Support CPU offline/online
x86/cpufeature: Add SEV_ES_GUEST CPU Feature
x86/sev-es: Add NMI state tracking

Tom Lendacky (18):
KVM: SVM: Add GHCB definitions
x86/cpufeatures: Add SEV-ES CPU feature
x86/sev-es: Add support for handling IOIO exceptions
x86/sev-es: Add CPUID handling to #VC handler
x86/sev-es: Add handler for MMIO events
x86/sev-es: Setup per-cpu GHCBs for the runtime handler
x86/sev-es: Add Runtime #VC Exception Handler
x86/sev-es: Handle MSR events
x86/sev-es: Handle DR7 read/write events
x86/sev-es: Handle WBINVD Events
x86/sev-es: Handle RDTSC Events
x86/sev-es: Handle RDPMC Events
x86/sev-es: Handle INVD Events
x86/sev-es: Handle MONITOR/MONITORX Events
x86/sev-es: Handle MWAIT/MWAITX Events
x86/sev-es: Handle VMMCALL Events
x86/kvm: Add KVM specific VMMCALL handling under SEV-ES
x86/realmode: Setup AP jump table

arch/x86/Kconfig | 1 +
arch/x86/boot/Makefile | 2 +-
arch/x86/boot/compressed/Makefile | 8 +-
arch/x86/boot/compressed/head_64.S | 41 ++
arch/x86/boot/compressed/ident_map_64.c | 320 +++++++++
arch/x86/boot/compressed/idt_64.c | 53 ++
arch/x86/boot/compressed/idt_handlers_64.S | 78 +++
arch/x86/boot/compressed/kaslr.c | 36 +-
arch/x86/boot/compressed/kaslr_64.c | 156 -----
arch/x86/boot/compressed/misc.h | 34 +-
arch/x86/boot/compressed/sev-es.c | 148 ++++
arch/x86/entry/entry_64.S | 52 ++
arch/x86/include/asm/cpu.h | 2 +-
arch/x86/include/asm/cpufeatures.h | 2 +
arch/x86/include/asm/desc.h | 2 +
arch/x86/include/asm/desc_defs.h | 3 +
arch/x86/include/asm/fpu/internal.h | 29 +-
arch/x86/include/asm/fpu/xcr.h | 32 +
arch/x86/include/asm/mem_encrypt.h | 5 +
arch/x86/include/asm/msr-index.h | 3 +
arch/x86/include/asm/processor.h | 1 +
arch/x86/include/asm/realmode.h | 4 +
arch/x86/include/asm/segment.h | 2 +-
arch/x86/include/asm/sev-es.h | 119 ++++
arch/x86/include/asm/svm.h | 103 +++
arch/x86/include/asm/trap_defs.h | 50 ++
arch/x86/include/asm/traps.h | 51 +-
arch/x86/include/asm/x86_init.h | 16 +-
arch/x86/include/uapi/asm/svm.h | 11 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/cpu/amd.c | 10 +-
arch/x86/kernel/cpu/scattered.c | 1 +
arch/x86/kernel/cpu/vmware.c | 48 +-
arch/x86/kernel/head64.c | 49 ++
arch/x86/kernel/head_32.S | 4 +-
arch/x86/kernel/head_64.S | 162 +++--
arch/x86/kernel/idt.c | 60 +-
arch/x86/kernel/kvm.c | 35 +-
arch/x86/kernel/nmi.c | 8 +
arch/x86/kernel/sev-es-shared.c | 721 ++++++++++++++++++++
arch/x86/kernel/sev-es.c | 748 +++++++++++++++++++++
arch/x86/kernel/smpboot.c | 4 +-
arch/x86/kernel/traps.c | 3 +
arch/x86/mm/extable.c | 1 +
arch/x86/mm/mem_encrypt.c | 11 +-
arch/x86/mm/mem_encrypt_identity.c | 3 +
arch/x86/realmode/init.c | 12 +
arch/x86/realmode/rm/header.S | 3 +
arch/x86/realmode/rm/trampoline_64.S | 20 +
arch/x86/tools/gen-insn-attr-x86.awk | 50 +-
tools/arch/x86/tools/gen-insn-attr-x86.awk | 50 +-
51 files changed, 3016 insertions(+), 352 deletions(-)
create mode 100644 arch/x86/boot/compressed/ident_map_64.c
create mode 100644 arch/x86/boot/compressed/idt_64.c
create mode 100644 arch/x86/boot/compressed/idt_handlers_64.S
delete mode 100644 arch/x86/boot/compressed/kaslr_64.c
create mode 100644 arch/x86/boot/compressed/sev-es.c
create mode 100644 arch/x86/include/asm/fpu/xcr.h
create mode 100644 arch/x86/include/asm/sev-es.h
create mode 100644 arch/x86/include/asm/trap_defs.h
create mode 100644 arch/x86/kernel/sev-es-shared.c
create mode 100644 arch/x86/kernel/sev-es.c

--
2.17.1

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