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, 161 insertions, 0 deletions

diff --git a/crypto/ecdsa-p1363.c b/crypto/ecdsa-p1363.c
new file mode 100644
index 000000000..e0c55c647
--- /dev/null
+++ b/crypto/ecdsa-p1363.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ECDSA P1363 signature encoding
+ *
+ * Copyright (c) 2024 Intel Corporation
+ */
+
+#include <linux/err.h>
+#include <linux/module.h>
+#include <crypto/algapi.h>
+#include <crypto/sig.h>
+#include <crypto/internal/ecc.h>
+#include <crypto/internal/sig.h>
+
+struct ecdsa_p1363_ctx {
+	struct crypto_sig *child;
+};
+
+static int ecdsa_p1363_verify(struct crypto_sig *tfm,
+			      const void *src, unsigned int slen,
+			      const void *digest, unsigned int dlen)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+	unsigned int keylen = DIV_ROUND_UP_POW2(crypto_sig_keysize(ctx->child),
+						BITS_PER_BYTE);
+	unsigned int ndigits = DIV_ROUND_UP_POW2(keylen, sizeof(u64));
+	struct ecdsa_raw_sig sig;
+
+	if (slen != 2 * keylen)
+		return -EINVAL;
+
+	ecc_digits_from_bytes(src, keylen, sig.r, ndigits);
+	ecc_digits_from_bytes(src + keylen, keylen, sig.s, ndigits);
+
+	return crypto_sig_verify(ctx->child, &sig, sizeof(sig), digest, dlen);
+}
+
+static unsigned int ecdsa_p1363_key_size(struct crypto_sig *tfm)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+
+	return crypto_sig_keysize(ctx->child);
+}
+
+static unsigned int ecdsa_p1363_max_size(struct crypto_sig *tfm)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+
+	return 2 * DIV_ROUND_UP_POW2(crypto_sig_keysize(ctx->child),
+				     BITS_PER_BYTE);
+}
+
+static unsigned int ecdsa_p1363_digest_size(struct crypto_sig *tfm)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+
+	return crypto_sig_digestsize(ctx->child);
+}
+
+static int ecdsa_p1363_set_pub_key(struct crypto_sig *tfm,
+				   const void *key, unsigned int keylen)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+
+	return crypto_sig_set_pubkey(ctx->child, key, keylen);
+}
+
+static int ecdsa_p1363_init_tfm(struct crypto_sig *tfm)
+{
+	struct sig_instance *inst = sig_alg_instance(tfm);
+	struct crypto_sig_spawn *spawn = sig_instance_ctx(inst);
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+	struct crypto_sig *child_tfm;
+
+	child_tfm = crypto_spawn_sig(spawn);
+	if (IS_ERR(child_tfm))
+		return PTR_ERR(child_tfm);
+
+	ctx->child = child_tfm;
+
+	return 0;
+}
+
+static void ecdsa_p1363_exit_tfm(struct crypto_sig *tfm)
+{
+	struct ecdsa_p1363_ctx *ctx = crypto_sig_ctx(tfm);
+
+	crypto_free_sig(ctx->child);
+}
+
+static void ecdsa_p1363_free(struct sig_instance *inst)
+{
+	struct crypto_sig_spawn *spawn = sig_instance_ctx(inst);
+
+	crypto_drop_sig(spawn);
+	kfree(inst);
+}
+
+static int ecdsa_p1363_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct crypto_sig_spawn *spawn;
+	struct sig_instance *inst;
+	struct sig_alg *ecdsa_alg;
+	u32 mask;
+	int err;
+
+	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SIG, &mask);
+	if (err)
+		return err;
+
+	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+
+	spawn = sig_instance_ctx(inst);
+
+	err = crypto_grab_sig(spawn, sig_crypto_instance(inst),
+			      crypto_attr_alg_name(tb[1]), 0, mask);
+	if (err)
+		goto err_free_inst;
+
+	ecdsa_alg = crypto_spawn_sig_alg(spawn);
+
+	err = -EINVAL;
+	if (strncmp(ecdsa_alg->base.cra_name, "ecdsa", 5) != 0)
+		goto err_free_inst;
+
+	err = crypto_inst_setname(sig_crypto_instance(inst), tmpl->name,
+				  &ecdsa_alg->base);
+	if (err)
+		goto err_free_inst;
+
+	inst->alg.base.cra_priority = ecdsa_alg->base.cra_priority;
+	inst->alg.base.cra_ctxsize = sizeof(struct ecdsa_p1363_ctx);
+
+	inst->alg.init = ecdsa_p1363_init_tfm;
+	inst->alg.exit = ecdsa_p1363_exit_tfm;
+
+	inst->alg.verify = ecdsa_p1363_verify;
+	inst->alg.key_size = ecdsa_p1363_key_size;
+	inst->alg.max_size = ecdsa_p1363_max_size;
+	inst->alg.digest_size = ecdsa_p1363_digest_size;
+	inst->alg.set_pub_key = ecdsa_p1363_set_pub_key;
+
+	inst->free = ecdsa_p1363_free;
+
+	err = sig_register_instance(tmpl, inst);
+	if (err) {
+err_free_inst:
+		ecdsa_p1363_free(inst);
+	}
+	return err;
+}
+
+struct crypto_template ecdsa_p1363_tmpl = {
+	.name = "p1363",
+	.create = ecdsa_p1363_create,
+	.module = THIS_MODULE,
+};
+
+MODULE_ALIAS_CRYPTO("p1363");