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, 91 insertions, 0 deletions

diff --git a/crypto/cipher.c b/crypto/cipher.c
new file mode 100644
index 000000000..c9dab656a
--- /dev/null
+++ b/crypto/cipher.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Cryptographic API.
+ *
+ * Single-block cipher operations.
+ *
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ * Copyright (c) 2005 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/internal/cipher.h>
+#include <linux/kernel.h>
+#include <linux/crypto.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include "internal.h"
+
+static int setkey_unaligned(struct crypto_cipher *tfm, const u8 *key,
+			    unsigned int keylen)
+{
+	struct cipher_alg *cia = crypto_cipher_alg(tfm);
+	unsigned long alignmask = crypto_cipher_alignmask(tfm);
+	int ret;
+	u8 *buffer, *alignbuffer;
+	unsigned long absize;
+
+	absize = keylen + alignmask;
+	buffer = kmalloc(absize, GFP_ATOMIC);
+	if (!buffer)
+		return -ENOMEM;
+
+	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
+	memcpy(alignbuffer, key, keylen);
+	ret = cia->cia_setkey(crypto_cipher_tfm(tfm), alignbuffer, keylen);
+	kfree_sensitive(buffer);
+	return ret;
+
+}
+
+int crypto_cipher_setkey(struct crypto_cipher *tfm,
+			 const u8 *key, unsigned int keylen)
+{
+	struct cipher_alg *cia = crypto_cipher_alg(tfm);
+	unsigned long alignmask = crypto_cipher_alignmask(tfm);
+
+	if (keylen < cia->cia_min_keysize || keylen > cia->cia_max_keysize)
+		return -EINVAL;
+
+	if ((unsigned long)key & alignmask)
+		return setkey_unaligned(tfm, key, keylen);
+
+	return cia->cia_setkey(crypto_cipher_tfm(tfm), key, keylen);
+}
+EXPORT_SYMBOL_NS_GPL(crypto_cipher_setkey, "CRYPTO_INTERNAL");
+
+static inline void cipher_crypt_one(struct crypto_cipher *tfm,
+				    u8 *dst, const u8 *src, bool enc)
+{
+	unsigned long alignmask = crypto_cipher_alignmask(tfm);
+	struct cipher_alg *cia = crypto_cipher_alg(tfm);
+	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
+		enc ? cia->cia_encrypt : cia->cia_decrypt;
+
+	if (unlikely(((unsigned long)dst | (unsigned long)src) & alignmask)) {
+		unsigned int bs = crypto_cipher_blocksize(tfm);
+		u8 buffer[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
+		u8 *tmp = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
+
+		memcpy(tmp, src, bs);
+		fn(crypto_cipher_tfm(tfm), tmp, tmp);
+		memcpy(dst, tmp, bs);
+	} else {
+		fn(crypto_cipher_tfm(tfm), dst, src);
+	}
+}
+
+void crypto_cipher_encrypt_one(struct crypto_cipher *tfm,
+			       u8 *dst, const u8 *src)
+{
+	cipher_crypt_one(tfm, dst, src, true);
+}
+EXPORT_SYMBOL_NS_GPL(crypto_cipher_encrypt_one, "CRYPTO_INTERNAL");
+
+void crypto_cipher_decrypt_one(struct crypto_cipher *tfm,
+			       u8 *dst, const u8 *src)
+{
+	cipher_crypt_one(tfm, dst, src, false);
+}
+EXPORT_SYMBOL_NS_GPL(crypto_cipher_decrypt_one, "CRYPTO_INTERNAL");