KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 138 insertions, 0 deletions

diff --git a/scripts/extract-module-sig.pl b/scripts/extract-module-sig.pl
new file mode 100755
index 000000000..36a2f59c4
--- /dev/null
+++ b/scripts/extract-module-sig.pl
@@ -0,0 +1,138 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# extract-mod-sig <part> <module-file>
+#
+# Reads the module file and writes out some or all of the signature
+# section to stdout.  Part is the bit to be written and is one of:
+#
+#  -0: The unsigned module, no signature data at all
+#  -a: All of the signature data, including magic number
+#  -d: Just the descriptor values as a sequence of numbers
+#  -n: Just the signer's name
+#  -k: Just the key ID
+#  -s: Just the crypto signature or PKCS#7 message
+#
+use warnings;
+use strict;
+
+die "Format: $0 -[0adnks] module-file >out\n"
+    if ($#ARGV != 1);
+
+my $part = $ARGV[0];
+my $modfile = $ARGV[1];
+
+my $magic_number = "~Module signature appended~\n";
+
+#
+# Read the module contents
+#
+open FD, "<$modfile" || die $modfile;
+binmode(FD);
+my @st = stat(FD);
+die "$modfile" unless (@st);
+my $buf = "";
+my $len = sysread(FD, $buf, $st[7]);
+die "$modfile" unless (defined($len));
+die "Short read on $modfile\n" unless ($len == $st[7]);
+close(FD) || die $modfile;
+
+print STDERR "Read ", $len, " bytes from module file\n";
+
+die "The file is too short to have a sig magic number and descriptor\n"
+    if ($len < 12 + length($magic_number));
+
+#
+# Check for the magic number and extract the information block
+#
+my $p = $len - length($magic_number);
+my $raw_magic = substr($buf, $p);
+
+die "Magic number not found at $len\n"
+    if ($raw_magic ne $magic_number);
+print STDERR "Found magic number at $len\n";
+
+$p -= 12;
+my $raw_info = substr($buf, $p, 12);
+
+my @info = unpack("CCCCCxxxN", $raw_info);
+my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
+
+if ($id_type == 0) {
+    print STDERR "Found PGP key identifier\n";
+} elsif ($id_type == 1) {
+    print STDERR "Found X.509 cert identifier\n";
+} elsif ($id_type == 2) {
+    print STDERR "Found PKCS#7/CMS encapsulation\n";
+} else {
+    print STDERR "Found unsupported identifier type $id_type\n";
+}
+
+#
+# Extract the three pieces of info data
+#
+die "Insufficient name+kid+sig data in file\n"
+    unless ($p >= $name_len + $kid_len + $sig_len);
+
+$p -= $sig_len;
+my $raw_sig = substr($buf, $p, $sig_len);
+$p -= $kid_len;
+my $raw_kid = substr($buf, $p, $kid_len);
+$p -= $name_len;
+my $raw_name = substr($buf, $p, $name_len);
+
+my $module_len = $p;
+
+if ($sig_len > 0) {
+    print STDERR "Found $sig_len bytes of signature [";
+    my $n = $sig_len > 16 ? 16 : $sig_len;
+    foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($kid_len > 0) {
+    print STDERR "Found $kid_len bytes of key identifier [";
+    my $n = $kid_len > 16 ? 16 : $kid_len;
+    foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($name_len > 0) {
+    print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
+}
+
+#
+# Produce the requested output
+#
+if ($part eq "-0") {
+    # The unsigned module, no signature data at all
+    binmode(STDOUT);
+    print substr($buf, 0, $module_len);
+} elsif ($part eq "-a") {
+    # All of the signature data, including magic number
+    binmode(STDOUT);
+    print substr($buf, $module_len);
+} elsif ($part eq "-d") {
+    # Just the descriptor values as a sequence of numbers
+    print join(" ", @info), "\n";
+} elsif ($part eq "-n") {
+    # Just the signer's name
+    print STDERR "No signer's name for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_name;
+} elsif ($part eq "-k") {
+    # Just the key identifier
+    print STDERR "No key ID for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_kid;
+} elsif ($part eq "-s") {
+    # Just the crypto signature or PKCS#7 message
+    binmode(STDOUT);
+    print $raw_sig;
+}