[pve-devel] [PATCH qemu-server] QEMU AMD SEV enable

Markus Frank m.frank at proxmox.com
Thu Jun 9 13:14:07 CEST 2022


This Patch is for enabling AMD SEV (Secure Encrypted Virtualization) support in
QEMU and for supporting other memory encryption technologies like INTEL MKTME
(Multi-key Total Memory Encryption) and AMD-SNP in the future.

Config-Example:
memory_encryption: type=sev,cbitpos=47,policy=0x0005,reduced-phys-bits=1

"reduced-phys-bios" and "cbitpos" are system specific and can be read out with
QMP. If not set by the user, a dummy-vm gets started to read QMP for these
variables out and save them to config. Afterwards, the dummy-vm gets stopped.

For a more detailed Explanation plus Requirements & Limitations
see my coherent pve-docs patch and the qemu documentation.

Signed-off-by: Markus Frank <m.frank at proxmox.com>
---
I could not test SEV-ES because I get a similar error to
https://www.mail-archive.com/devel@edk2.groups.io/msg38521.html
But I still get the same error on master and mentioned patched versions.
On some older versions I just get "kvm: SEV-ES reset address is zero
kvm: failed to locate and/or save reset vector"

Maybe I will report my error to the edk2 project or find a way to fix
it, when I know more about it.

I also could not test SEV-SNP, because I do not have a EPYC 7003 to test
on and there is also no support in the Linux Kernel yet. SEV-SNP support
should be in Linux 5.19:
https://www.phoronix.com/scan.php?page=news_item&px=AMD-SEV-SNP-Arrives-Linux-5.19
patched kernel-fork: https://github.com/AMDESE/linux/tree/sev-snp-5.18-rc3

 PVE/QemuServer.pm | 133 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 133 insertions(+)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index e9aa248..abc21d4 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -174,6 +174,55 @@ my $agent_fmt = {
     },
 };
 
+my $memory_encryption_fmt = {
+    type => {
+	type => 'string',
+	default_key => 1,
+	description => "Memory Encryption Type:"
+	    ."for AMD SEV -> 'memory_encryption: type=sev'"
+	    ."for AMD SEV-SNP -> 'memory_encryption: type=sev-snp'"
+	    ."for AMD SEV-ES -> use 'sev' and change policy to between 0x4 and 0x7"
+	    ."(Bit-2 has to be set 1 (LSB 0 bit numbering))"
+	    ."(sev requires edk2-ovmf & on guest: up-to-date kernel + sev support &"
+	    ."on host: add kernel-parameters 'mem_encrypt=on kvm_amd.sev=1')"
+	    ."see https://github.com/AMDESE/AMDSEV",
+	format_description => "qemu-memory-encryption-type",
+	#pattern => '(sev|sev-snp|mktme)',
+	pattern => '(sev|sev-snp)',
+	default => "",
+	maxLength => 10,
+    },
+    'reduced-phys-bits' => {
+	description => "Number of bits the physical address space is reduced by. System dependent",
+	type => 'integer',
+	default => 1,
+	optional => 1,
+	minium => 0,
+	maximum => 100,
+    },
+    cbitpos => {
+	description => "C-bit: marks if a memory page is protected. System dependent",
+	type => 'integer',
+	default => 47,
+	optional => 1,
+	minium => 0,
+	maximum => 100,
+    },
+    policy => {
+	description => "SEV Guest Policy"
+	    ."see Capter 3:"
+	    ."https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf"
+	    ."& https://www.qemu.org/docs/master/system/i386/amd-memory-encryption.html",
+	format_description => "qemu-memory-encryption-policy",
+	type => 'string',
+	default => '0x0000',
+	pattern => '0[xX][0-9a-fA-F]{1,4}',
+	optional => 1,
+	maxLength => 6,
+    },
+};
+PVE::JSONSchema::register_format('pve-qemu-memory-encryption-fmt', $memory_encryption_fmt);
+
 my $vga_fmt = {
     type => {
 	description => "Select the VGA type.",
@@ -348,6 +397,12 @@ my $confdesc = {
 	minimum => 16,
 	default => 512,
     },
+    memory_encryption => {
+	description => "Memory Encryption",
+	optional => 1,
+	format => 'pve-qemu-memory-encryption-fmt',
+	type => 'string',
+    },
     balloon => {
 	optional => 1,
 	type => 'integer',
@@ -2107,6 +2162,16 @@ sub parse_guest_agent {
     return $res;
 }
 
+sub parse_memory_encryption {
+    my ($value) = @_;
+
+    return if !$value;
+
+    my $res = eval { parse_property_string($memory_encryption_fmt, $value) };
+    warn $@ if $@;
+    return $res;
+}
+
 sub get_qga_key {
     my ($conf, $key) = @_;
     return undef if !defined($conf->{agent});
@@ -4079,6 +4144,74 @@ sub config_to_command {
     }
     push @$machineFlags, "type=${machine_type_min}";
 
+    # Memory Encryption configuration
+    my $memory_encryption = parse_memory_encryption($conf->{'memory_encryption'});
+
+    # Die if bios is not ovmf
+    if (
+	$conf->{'memory_encryption'}
+	&& $memory_encryption->{type} eq 'sev'
+	&& !$conf->{bios} eq 'ovmf'
+    ) {
+	die "SEV needs ovmf";
+    }
+
+    # AMD SEV
+    if ($conf->{'memory_encryption'} && $memory_encryption->{type} =~ /(sev|sev-snp)/) {
+	# Get reduced-phys-bits & cbitpos from QMP, if not set
+	if (
+	    !$memory_encryption->{'reduced-phys-bits'}
+	    || !$memory_encryption->{cbitpos}
+	) {
+	    my $fakevmid = -1;
+	    my $qemu_cmd = get_command_for_arch($arch);
+	    my $pidfile = PVE::QemuServer::Helpers::pidfile_name($fakevmid);
+	    my $default_machine = $default_machines->{$arch};
+	    my $cmd = [
+		$qemu_cmd,
+		'-machine', $default_machine,
+		'-display', 'none',
+		'-chardev', "socket,id=qmp,path=/var/run/qemu-server/$fakevmid.qmp,server=on,wait=off",
+		'-mon', 'chardev=qmp,mode=control',
+		'-pidfile', $pidfile,
+		'-S', '-daemonize'
+	    ];
+	    if (!$kvm) {
+		push @$cmd, '-accel', 'tcg';
+	    }
+	    my $rc = run_command($cmd, noerr => 1, quiet => 0);
+	    die "QEMU flag querying VM exited with code " . $rc if $rc;
+	    my $res = mon_cmd($fakevmid, 'query-sev-capabilities');
+	    $memory_encryption->{'reduced-phys-bits'} = $res->{'reduced-phys-bits'};
+	    $memory_encryption->{cbitpos} = $res->{cbitpos};
+	    $conf->{'memory_encryption'} = PVE::JSONSchema::print_property_string(
+		$memory_encryption,
+		$memory_encryption_fmt
+	    );
+	    PVE::QemuConfig->write_config($vmid, $conf);
+	    vm_stop(undef, $fakevmid, 1, 1, 10, 0, 1);
+	}
+
+	# qemu-Example: -object 'sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1';
+	# see https://www.qemu.org/docs/master/system/i386/amd-memory-encryption.html
+	my $memobjcmd = "";
+	if ($memory_encryption->{type} eq 'sev-snp') {
+	    # https://github.com/AMDESE/AMDSEV/tree/sev-snp-devel
+	    $memobjcmd = $memobjcmd.'sev-snp-guest,';
+	} else {
+	    $memobjcmd = $memobjcmd.'sev-guest,';
+	}
+	$memobjcmd = $memobjcmd . 'id=sev0,cbitpos='.$memory_encryption->{cbitpos}
+	    .',reduced-phys-bits='.$memory_encryption->{'reduced-phys-bits'};
+	if ($memory_encryption->{type} eq 'sev' && $memory_encryption->{policy}) {
+	    $memobjcmd = $memobjcmd.',policy='.$memory_encryption->{policy}
+	}
+	push @$devices, '-object' , $memobjcmd;
+	# old qemu-Example: -machine 'type=q35+pve0,memory-encryption=sev0'
+	# https://fossies.org/linux/qemu/docs/system/confidential-guest-support.rst
+	push @$machineFlags, 'confidential-guest-support=sev0';
+    }
+
     push @$cmd, @$devices;
     push @$cmd, '-rtc', join(',', @$rtcFlags) if scalar(@$rtcFlags);
     push @$cmd, '-machine', join(',', @$machineFlags) if scalar(@$machineFlags);
-- 
2.30.2





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