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, 247 insertions, 0 deletions

diff --git a/crypto/ecdh.c b/crypto/ecdh.c
new file mode 100644
index 000000000..9f0b93b31
--- /dev/null
+++ b/crypto/ecdh.c
@@ -0,0 +1,247 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* ECDH key-agreement protocol
+ *
+ * Copyright (c) 2016, Intel Corporation
+ * Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
+ */
+
+#include <linux/module.h>
+#include <crypto/internal/ecc.h>
+#include <crypto/internal/kpp.h>
+#include <crypto/kpp.h>
+#include <crypto/ecdh.h>
+#include <linux/scatterlist.h>
+
+struct ecdh_ctx {
+	unsigned int curve_id;
+	unsigned int ndigits;
+	u64 private_key[ECC_MAX_DIGITS];
+};
+
+static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
+{
+	return kpp_tfm_ctx(tfm);
+}
+
+static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
+			   unsigned int len)
+{
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+	struct ecdh params;
+	int ret = 0;
+
+	if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
+	    params.key_size > sizeof(u64) * ctx->ndigits)
+		return -EINVAL;
+
+	memset(ctx->private_key, 0, sizeof(ctx->private_key));
+
+	if (!params.key || !params.key_size)
+		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
+				       ctx->private_key);
+
+	ecc_digits_from_bytes(params.key, params.key_size,
+			      ctx->private_key, ctx->ndigits);
+
+	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
+			     ctx->private_key, params.key_size) < 0) {
+		memzero_explicit(ctx->private_key, params.key_size);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static int ecdh_compute_value(struct kpp_request *req)
+{
+	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+	u64 *public_key;
+	u64 *shared_secret = NULL;
+	void *buf;
+	size_t copied, nbytes, public_key_sz;
+	int ret = -ENOMEM;
+
+	nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+	/* Public part is a point thus it has both coordinates */
+	public_key_sz = 2 * nbytes;
+
+	public_key = kmalloc(public_key_sz, GFP_KERNEL);
+	if (!public_key)
+		return -ENOMEM;
+
+	if (req->src) {
+		shared_secret = kmalloc(nbytes, GFP_KERNEL);
+		if (!shared_secret)
+			goto free_pubkey;
+
+		/* from here on it's invalid parameters */
+		ret = -EINVAL;
+
+		/* must have exactly two points to be on the curve */
+		if (public_key_sz != req->src_len)
+			goto free_all;
+
+		copied = sg_copy_to_buffer(req->src,
+					   sg_nents_for_len(req->src,
+							    public_key_sz),
+					   public_key, public_key_sz);
+		if (copied != public_key_sz)
+			goto free_all;
+
+		ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
+						ctx->private_key, public_key,
+						shared_secret);
+
+		buf = shared_secret;
+	} else {
+		ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
+				       ctx->private_key, public_key);
+		buf = public_key;
+		nbytes = public_key_sz;
+	}
+
+	if (ret < 0)
+		goto free_all;
+
+	/* might want less than we've got */
+	nbytes = min_t(size_t, nbytes, req->dst_len);
+	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
+								nbytes),
+				     buf, nbytes);
+	if (copied != nbytes)
+		ret = -EINVAL;
+
+	/* fall through */
+free_all:
+	kfree_sensitive(shared_secret);
+free_pubkey:
+	kfree(public_key);
+	return ret;
+}
+
+static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
+{
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+
+	/* Public key is made of two coordinates, add one to the left shift */
+	return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
+}
+
+static int ecdh_nist_p192_init_tfm(struct crypto_kpp *tfm)
+{
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+
+	ctx->curve_id = ECC_CURVE_NIST_P192;
+	ctx->ndigits = ECC_CURVE_NIST_P192_DIGITS;
+
+	return 0;
+}
+
+static struct kpp_alg ecdh_nist_p192 = {
+	.set_secret = ecdh_set_secret,
+	.generate_public_key = ecdh_compute_value,
+	.compute_shared_secret = ecdh_compute_value,
+	.max_size = ecdh_max_size,
+	.init = ecdh_nist_p192_init_tfm,
+	.base = {
+		.cra_name = "ecdh-nist-p192",
+		.cra_driver_name = "ecdh-nist-p192-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecdh_ctx),
+	},
+};
+
+static int ecdh_nist_p256_init_tfm(struct crypto_kpp *tfm)
+{
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+
+	ctx->curve_id = ECC_CURVE_NIST_P256;
+	ctx->ndigits = ECC_CURVE_NIST_P256_DIGITS;
+
+	return 0;
+}
+
+static struct kpp_alg ecdh_nist_p256 = {
+	.set_secret = ecdh_set_secret,
+	.generate_public_key = ecdh_compute_value,
+	.compute_shared_secret = ecdh_compute_value,
+	.max_size = ecdh_max_size,
+	.init = ecdh_nist_p256_init_tfm,
+	.base = {
+		.cra_name = "ecdh-nist-p256",
+		.cra_driver_name = "ecdh-nist-p256-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecdh_ctx),
+	},
+};
+
+static int ecdh_nist_p384_init_tfm(struct crypto_kpp *tfm)
+{
+	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+
+	ctx->curve_id = ECC_CURVE_NIST_P384;
+	ctx->ndigits = ECC_CURVE_NIST_P384_DIGITS;
+
+	return 0;
+}
+
+static struct kpp_alg ecdh_nist_p384 = {
+	.set_secret = ecdh_set_secret,
+	.generate_public_key = ecdh_compute_value,
+	.compute_shared_secret = ecdh_compute_value,
+	.max_size = ecdh_max_size,
+	.init = ecdh_nist_p384_init_tfm,
+	.base = {
+		.cra_name = "ecdh-nist-p384",
+		.cra_driver_name = "ecdh-nist-p384-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecdh_ctx),
+	},
+};
+
+static bool ecdh_nist_p192_registered;
+
+static int __init ecdh_init(void)
+{
+	int ret;
+
+	/* NIST p192 will fail to register in FIPS mode */
+	ret = crypto_register_kpp(&ecdh_nist_p192);
+	ecdh_nist_p192_registered = ret == 0;
+
+	ret = crypto_register_kpp(&ecdh_nist_p256);
+	if (ret)
+		goto nist_p256_error;
+
+	ret = crypto_register_kpp(&ecdh_nist_p384);
+	if (ret)
+		goto nist_p384_error;
+
+	return 0;
+
+nist_p384_error:
+	crypto_unregister_kpp(&ecdh_nist_p256);
+
+nist_p256_error:
+	if (ecdh_nist_p192_registered)
+		crypto_unregister_kpp(&ecdh_nist_p192);
+	return ret;
+}
+
+static void __exit ecdh_exit(void)
+{
+	if (ecdh_nist_p192_registered)
+		crypto_unregister_kpp(&ecdh_nist_p192);
+	crypto_unregister_kpp(&ecdh_nist_p256);
+	crypto_unregister_kpp(&ecdh_nist_p384);
+}
+
+module_init(ecdh_init);
+module_exit(ecdh_exit);
+MODULE_ALIAS_CRYPTO("ecdh");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ECDH generic algorithm");