[pve-devel] [PATCH qemu-server v6 2/3] config: QEMU AMD SEV enable

[Markus Frank <m.frank@proxmox.com>]

This patch is for enabling AMD SEV (Secure Encrypted
Virtualization) support in QEMU

VM-Config-Examples:
amd_sev: type=std,nodbg=1,noks=1
amd_sev: es,nodbg=1,kernel-hashes=1

Node-Config-Example (gets generated automatically):
amd_sev: cbitpos=47,reduced-phys-bios=1

kernel-hashes, reduced-phys-bios & cbitpos correspond to the varibles
with the same name in qemu.

kernel-hashes=1 adds kernel-hashes to enable measured linux kernel
launch since it is per default off for backward compatibility.

reduced-phys-bios and cbitpos are system specific and are read out by
a C program started by the amd-sev-support.service on boot and saved
to the /run/amd-sev-params file. This file is parsed and than used by
qemu-server to correctly start a AMD SEV VM.

type=std stands for standard sev to differentiate it from sev-es (es)
or sev-snp (snp) when support is upstream.

QEMU's sev-guest policy gets calculated with the parameters nodbg & noks
These parameters correspond to policy-bits 0 & 1.
If type is 'es' than policy-bit 2 gets set to 1 to activate SEV-ES.
Policy bit 3 (nosend) is always set to 1, because migration
features for sev are not upstream yet and are attackable.

SEV-ES is highly experimental since it could not be tested.

see coherent doc patch

Signed-off-by: Markus Frank <m.frank@proxmox.com>
---
v6:
* rebase on master
* removed unused $sev_node_fmt object

v5:
* parse /run/amd-sev-params for hardware parameters
* removed NodeConfig dependency
* only disallow live-migration and snapshots with vmstate
  -> allow offline migration and snapshots without vmstate

v4:
* reduced lines of code
* added text that SEV-ES is experimental

 PVE/API2/Qemu.pm   | 10 ++++++
 PVE/QemuMigrate.pm |  4 +++
 PVE/QemuServer.pm  | 83 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+)

diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
index 2a349c8..2e8d654 100644
--- a/PVE/API2/Qemu.pm
+++ b/PVE/API2/Qemu.pm
@@ -4512,6 +4512,10 @@ __PACKAGE__->register_method({
 	    push $local_resources->@*, "clipboard=vnc";
 	}
 
+	if ($res->{running} && $vmconf->{amd_sev}) {
+	    push $local_resources->@*, "amd_sev";
+	}
+
 	# if vm is not running, return target nodes where local storage/mapped devices are available
 	# for offline migration
 	if (!$res->{running}) {
@@ -5192,6 +5196,12 @@ __PACKAGE__->register_method({
 	die "unable to use snapshot name 'pending' (reserved name)\n"
 	    if lc($snapname) eq 'pending';
 
+	my $conf = PVE::QemuConfig->load_config($vmid);
+	if ($param->{vmstate} && $conf->{amd_sev}) {
+	    die "Snapshots that include memory are not supported while memory"
+		." is encrypted by AMD SEV.\n"
+	}
+
 	my $realcmd = sub {
 	    PVE::Cluster::log_msg('info', $authuser, "snapshot VM $vmid: $snapname");
 	    PVE::QemuConfig->snapshot_create($vmid, $snapname, $param->{vmstate},
diff --git a/PVE/QemuMigrate.pm b/PVE/QemuMigrate.pm
index 8d9b35a..7db18b2 100644
--- a/PVE/QemuMigrate.pm
+++ b/PVE/QemuMigrate.pm
@@ -260,6 +260,10 @@ sub prepare {
 	die "VMs with 'clipboard' set to 'vnc' are not live migratable!\n";
     }
 
+    if ($running && $conf->{'amd_sev'}) {
+	die "VMs with AMD SEV are not live migratable!\n";
+    }
+
     my $vollist = PVE::QemuServer::get_vm_volumes($conf);
 
     my $storages = {};
diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 28e630d..b6e2713 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -177,6 +177,40 @@ my $agent_fmt = {
     },
 };
 
+my $sev_fmt = {
+    type => {
+	description => "Enable standard SEV with type='std' or enable experimental SEV-ES"
+	." with the 'es' option.",
+	type => 'string',
+	default_key => 1,
+	format_description => "qemu-sev-type",
+	enum => ['std', 'es'],
+	maxLength => 3,
+    },
+    nodbg => {
+	description => "Sets policy bit 0 to 1 to disallow debugging of guest",
+	type => 'boolean',
+	format_description => "qemu-sev-nodbg",
+	default => 0,
+	optional => 1,
+    },
+    noks => {
+	description => "Sets policy bit 1 to 1 to disallow key sharing with other guests",
+	type => 'boolean',
+	format_description => "qemu-sev-noks",
+	default => 0,
+	optional => 1,
+    },
+    "kernel-hashes" => {
+	description => "Add kernel hashes to guest firmware for measured linux kernel launch",
+	type => 'boolean',
+	format_description => "qemu-sev-kernel-hashes",
+	default => 0,
+	optional => 1,
+    },
+};
+PVE::JSONSchema::register_format('pve-qemu-sev-fmt', $sev_fmt);
+
 my $vga_fmt = {
     type => {
 	description => "Select the VGA type.",
@@ -358,6 +392,12 @@ my $confdesc = {
 	description => "Memory properties.",
 	format => $PVE::QemuServer::Memory::memory_fmt
     },
+    amd_sev => {
+	description => "Secure Encrypted Virtualization (SEV) features by AMD CPUs",
+	optional => 1,
+	format => 'pve-qemu-sev-fmt',
+	type => 'string',
+    },
     balloon => {
 	optional => 1,
 	type => 'integer',
@@ -4091,6 +4131,39 @@ sub config_to_command {
 	}
     }
 
+    if ($conf->{amd_sev}) {
+	if ($conf->{bios} && $conf->{bios} ne 'ovmf') {
+	    die "For using SEV you need to change your guest bios to ovmf.\n";
+	}
+
+	my $amd_sev_conf = parse_property_string($sev_fmt, $conf->{amd_sev});
+	my $sev_hw_params = get_sev_hw_parameters();
+
+	if (!$sev_hw_params->{sev}) {
+	    die "Your CPU does not support AMD SEV!\n";
+	}
+	if ($amd_sev_conf->{type} eq 'es' && !$sev_hw_params->{'sev-es'}) {
+	    die "Your CPU does not support AMD SEV-ES!\n";
+	}
+
+	my $sev_mem_object = 'sev-guest,id=sev0'
+	    .',cbitpos='.$sev_hw_params->{cbitpos}
+	    .',reduced-phys-bits='.$sev_hw_params->{'reduced-phys-bits'};
+
+	my $policy = 0b0;
+	$policy += 0b1 if ($amd_sev_conf->{nodbg});
+	$policy += 0b10 if ($amd_sev_conf->{noks});
+	$policy += 0b100 if ($amd_sev_conf->{type} eq 'es');
+	# disable migration with bit 3 nosend to prevent amd-sev-migration-attack
+	$policy += 0b1000;
+
+	$sev_mem_object .= ',policy='.sprintf("%#x", $policy);
+	$sev_mem_object .= ',kernel-hashes=on' if ($amd_sev_conf->{'kernel-hashes'});
+
+	push @$devices, '-object' , $sev_mem_object;
+	push @$machineFlags, 'confidential-guest-support=sev0';
+    }
+
     push @$cmd, @$devices;
     push @$cmd, '-rtc', join(',', @$rtcFlags) if scalar(@$rtcFlags);
     push @$cmd, '-machine', join(',', @$machineFlags) if scalar(@$machineFlags);
@@ -4134,6 +4207,16 @@ sub check_rng_source {
     }
 }
 
+sub get_sev_hw_parameters {
+    # Get reduced-phys-bits & cbitpos from /run/amd-sev-params
+    my $filename = '/run/amd-sev-params';
+    open my $fh, '<', $filename or die "Could not open '$filename' for reading: $!";
+    my $json_text = do { local $/; <$fh> };
+    close $fh;
+    my $sev_params = JSON->new->decode($json_text);
+    return $sev_params;
+}
+
 sub spice_port {
     my ($vmid) = @_;
 
-- 
2.39.2



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