[pve-devel] [PATCH qemu-server v10 2/4] config: add AMD SEV support

[Dominik Csapak]

comments inline:

On 5/10/24 13:47, Markus Frank wrote:
> This patch is for enabling AMD SEV (Secure Encrypted Virtualization)
> support in QEMU.
> 
> VM-Config-Examples:
> amd_sev: type=std,no-debug=1,no-key-sharing=1
> amd_sev: es,no-debug=1,kernel-hashes=1
> 
> kernel-hashes, reduced-phys-bios & cbitpos correspond to the variables
> 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
> the query-machine-capabilities.service on boot and saved to the
> /run/qemu-server/host-hw-capabilities.json 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 at proxmox.com>
> ---
> changes v10:
> * also die if the BIOS is not set, since the default is SeaBIOS
> 
>   PVE/API2/Qemu.pm   | 11 +++++++
>   PVE/QemuMigrate.pm |  4 +++
>   PVE/QemuServer.pm  | 79 ++++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 94 insertions(+)
> 
> diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
> index 2a349c8..c29809d 100644
> --- a/PVE/API2/Qemu.pm
> +++ b/PVE/API2/Qemu.pm
> @@ -4512,6 +4512,11 @@ __PACKAGE__->register_method({
>   	    push $local_resources->@*, "clipboard=vnc";
>   	}
>   
> +	# do not allow live migration with AMD SEV enabled
> +	if ($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 +5197,12 @@ __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"
> +	}
> +

you do it for snapshots, but it's missing for suspend to disk, where we
basically migrate into a file

>   	my $realcmd = sub {
>   	    PVE::Cluster::log_msg('info', $authuser, "snapshot VM $vmid: $snapname");
>   	    PVE::QemuConfig->snapshot_create($vmid, $snapname, $param->{vmstate},
> diff --git a/PVE/QemuMigrate.pm b/PVE/QemuMigrate.pm
> index 8d9b35a..340402a 100644
> --- a/PVE/QemuMigrate.pm
> +++ b/PVE/QemuMigrate.pm
> @@ -260,6 +260,10 @@ sub prepare {
>   	die "VMs with 'clipboard' set to 'vnc' are not live migratable!\n";
>       }
>   
> +    if ($running && $conf->{'amd_sev'}) {
> +	die "cannot live-migrate VM when AMD SEV is enabled.\n";
> +    }
> +
>       my $vollist = PVE::QemuServer::get_vm_volumes($conf);
>   
>       my $storages = {};
> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
> index 82e7d6a..92960c5 100644
> --- a/PVE/QemuServer.pm
> +++ b/PVE/QemuServer.pm
> @@ -177,6 +177,37 @@ 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 => "sev-type",
> +	enum => ['std', 'es'],
> +	maxLength => 3,
> +    },
> +    'no-debug' => {
> +	description => "Sets policy bit 0 to 1 to disallow debugging of guest",
> +	type => 'boolean',
> +	default => 0,
> +	optional => 1,
> +    },
> +    'no-key-sharing' => {
> +	description => "Sets policy bit 1 to 1 to disallow key sharing with other guests",
> +	type => 'boolean',
> +	default => 0,
> +	optional => 1,
> +    },
> +    "kernel-hashes" => {
> +	description => "Add kernel hashes to guest firmware for measured linux kernel launch",
> +	type => 'boolean',
> +	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 +389,12 @@ my $confdesc = {
>   	description => "Memory properties.",
>   	format => $PVE::QemuServer::Memory::memory_fmt
>       },
> +    amd_sev => {
> +	description => "Secure Encrypted Virtualization (SEV) features by AMD CPUs",
> +	optional => 1,
> +	format => 'pve-qemu-sev-fmt',
> +	type => 'string',
> +    },
>       balloon => {
>   	optional => 1,
>   	type => 'integer',
> @@ -4091,6 +4128,39 @@ sub config_to_command {
>   	}
>       }
>   
> +    if ($conf->{amd_sev}) {
> +	if (!$conf->{bios} || ($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 $sev_hw_caps = get_hw_capabilities()->{'amd-sev'};
> +
> +	if (!$sev_hw_caps->{'sev-support'}) {
> +	    die "Your CPU does not support AMD SEV!\n";
> +	}
> +	if ($amd_sev_conf->{type} eq 'es' && !$sev_hw_caps->{'sev-support-es'}) {
> +	    die "Your CPU does not support AMD SEV-ES!\n";
> +	}
> +
> +	my $sev_mem_object = 'sev-guest,id=sev0'
> +	    .',cbitpos='.$sev_hw_caps->{cbitpos}
> +	    .',reduced-phys-bits='.$sev_hw_caps->{'reduced-phys-bits'};
> +
> +	my $policy = 0b0;
> +	$policy += 0b1 if ($amd_sev_conf->{'no-debug'});
> +	$policy += 0b10 if ($amd_sev_conf->{'no-key-sharing'});
> +	$policy += 0b100 if ($amd_sev_conf->{type} eq 'es');
> +	# disable migration with bit 3 nosend to prevent amd-sev-migration-attack
> +	$policy += 0b1000;

isn't it possible to keep the bitlength identically? makes it easier to compare
e.g. like this:

my $policy = 0b0000;
$policy += 0b0001 if ...
$policy += 0b0010 if ...

etc..

> +
> +	$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';
> +    }
> +

also i'd prefer to put this whole block into e.g. PVE/QemuServer/CPUConfig

so 'config_to_command' does not get more bloated than it already is

>       push @$cmd, @$devices;
>       push @$cmd, '-rtc', join(',', @$rtcFlags) if scalar(@$rtcFlags);
>       push @$cmd, '-machine', join(',', @$machineFlags) if scalar(@$machineFlags);
> @@ -4134,6 +4204,15 @@ sub check_rng_source {
>       }
>   }
>   
> +sub get_hw_capabilities {
> +    # Get reduced-phys-bits & cbitpos from host-hw-capabilities.json
> +    my $filename = '/run/qemu-server/host-hw-capabilities.json';
> +    my $json_text = PVE::Tools::file_get_contents($filename);
> +    ($json_text) = $json_text =~ /(.*)/; # untaint json text
> +    my $hw_capabilities = decode_json($json_text);
> +    return $hw_capabilities;
> +}
> +

also this maybe? though it could also live in 'Helpers'

>   sub spice_port {
>       my ($vmid) = @_;
>