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, 480 insertions, 0 deletions

diff --git a/crypto/hctr2.c b/crypto/hctr2.c
new file mode 100644
index 000000000..cfc2343bc
--- /dev/null
+++ b/crypto/hctr2.c
@@ -0,0 +1,480 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * HCTR2 length-preserving encryption mode
+ *
+ * Copyright 2021 Google LLC
+ */
+
+
+/*
+ * HCTR2 is a length-preserving encryption mode that is efficient on
+ * processors with instructions to accelerate AES and carryless
+ * multiplication, e.g. x86 processors with AES-NI and CLMUL, and ARM
+ * processors with the ARMv8 crypto extensions.
+ *
+ * For more details, see the paper: "Length-preserving encryption with HCTR2"
+ * (https://eprint.iacr.org/2021/1441.pdf)
+ */
+
+#include <crypto/gf128hash.h>
+#include <crypto/internal/cipher.h>
+#include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
+#include <linux/module.h>
+
+#define BLOCKCIPHER_BLOCK_SIZE		16
+
+/*
+ * The specification allows variable-length tweaks, but Linux's crypto API
+ * currently only allows algorithms to support a single length.  The "natural"
+ * tweak length for HCTR2 is 16, since that fits into one POLYVAL block for
+ * the best performance.  But longer tweaks are useful for fscrypt, to avoid
+ * needing to derive per-file keys.  So instead we use two blocks, or 32 bytes.
+ */
+#define TWEAK_SIZE		32
+
+struct hctr2_instance_ctx {
+	struct crypto_cipher_spawn blockcipher_spawn;
+	struct crypto_skcipher_spawn xctr_spawn;
+};
+
+struct hctr2_tfm_ctx {
+	struct crypto_cipher *blockcipher;
+	struct crypto_skcipher *xctr;
+	struct polyval_key poly_key;
+	struct polyval_elem hashed_tweaklens[2];
+	u8 L[BLOCKCIPHER_BLOCK_SIZE];
+};
+
+struct hctr2_request_ctx {
+	u8 first_block[BLOCKCIPHER_BLOCK_SIZE];
+	u8 xctr_iv[BLOCKCIPHER_BLOCK_SIZE];
+	struct scatterlist *bulk_part_dst;
+	struct scatterlist *bulk_part_src;
+	struct scatterlist sg_src[2];
+	struct scatterlist sg_dst[2];
+	struct polyval_elem hashed_tweak;
+	/*
+	 * skcipher sub-request size is unknown at compile-time, so it needs to
+	 * go after the members with known sizes.
+	 */
+	union {
+		struct polyval_ctx poly_ctx;
+		struct skcipher_request xctr_req;
+	} u;
+};
+
+/*
+ * The input data for each HCTR2 hash step begins with a 16-byte block that
+ * contains the tweak length and a flag that indicates whether the input is evenly
+ * divisible into blocks.  Since this implementation only supports one tweak
+ * length, we precompute the two hash states resulting from hashing the two
+ * possible values of this initial block.  This reduces by one block the amount of
+ * data that needs to be hashed for each encryption/decryption
+ *
+ * These precomputed hashes are stored in hctr2_tfm_ctx.
+ */
+static void hctr2_hash_tweaklens(struct hctr2_tfm_ctx *tctx)
+{
+	struct polyval_ctx ctx;
+
+	for (int has_remainder = 0; has_remainder < 2; has_remainder++) {
+		const __le64 tweak_length_block[2] = {
+			cpu_to_le64(TWEAK_SIZE * 8 * 2 + 2 + has_remainder),
+		};
+
+		polyval_init(&ctx, &tctx->poly_key);
+		polyval_update(&ctx, (const u8 *)&tweak_length_block,
+			       sizeof(tweak_length_block));
+		static_assert(sizeof(tweak_length_block) == POLYVAL_BLOCK_SIZE);
+		polyval_export_blkaligned(
+			&ctx, &tctx->hashed_tweaklens[has_remainder]);
+	}
+	memzero_explicit(&ctx, sizeof(ctx));
+}
+
+static int hctr2_setkey(struct crypto_skcipher *tfm, const u8 *key,
+			unsigned int keylen)
+{
+	struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+	u8 hbar[BLOCKCIPHER_BLOCK_SIZE];
+	int err;
+
+	crypto_cipher_clear_flags(tctx->blockcipher, CRYPTO_TFM_REQ_MASK);
+	crypto_cipher_set_flags(tctx->blockcipher,
+				crypto_skcipher_get_flags(tfm) &
+				CRYPTO_TFM_REQ_MASK);
+	err = crypto_cipher_setkey(tctx->blockcipher, key, keylen);
+	if (err)
+		return err;
+
+	crypto_skcipher_clear_flags(tctx->xctr, CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_set_flags(tctx->xctr,
+				  crypto_skcipher_get_flags(tfm) &
+				  CRYPTO_TFM_REQ_MASK);
+	err = crypto_skcipher_setkey(tctx->xctr, key, keylen);
+	if (err)
+		return err;
+
+	memset(hbar, 0, sizeof(hbar));
+	crypto_cipher_encrypt_one(tctx->blockcipher, hbar, hbar);
+
+	memset(tctx->L, 0, sizeof(tctx->L));
+	tctx->L[0] = 0x01;
+	crypto_cipher_encrypt_one(tctx->blockcipher, tctx->L, tctx->L);
+
+	static_assert(sizeof(hbar) == POLYVAL_BLOCK_SIZE);
+	polyval_preparekey(&tctx->poly_key, hbar);
+	memzero_explicit(hbar, sizeof(hbar));
+
+	hctr2_hash_tweaklens(tctx);
+	return 0;
+}
+
+static void hctr2_hash_tweak(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+	struct hctr2_request_ctx *rctx = skcipher_request_ctx(req);
+	struct polyval_ctx *poly_ctx = &rctx->u.poly_ctx;
+	bool has_remainder = req->cryptlen % POLYVAL_BLOCK_SIZE;
+
+	polyval_import_blkaligned(poly_ctx, &tctx->poly_key,
+				  &tctx->hashed_tweaklens[has_remainder]);
+	polyval_update(poly_ctx, req->iv, TWEAK_SIZE);
+
+	// Store the hashed tweak, since we need it when computing both
+	// H(T || N) and H(T || V).
+	static_assert(TWEAK_SIZE % POLYVAL_BLOCK_SIZE == 0);
+	polyval_export_blkaligned(poly_ctx, &rctx->hashed_tweak);
+}
+
+static void hctr2_hash_message(struct skcipher_request *req,
+			       struct scatterlist *sgl,
+			       u8 digest[POLYVAL_DIGEST_SIZE])
+{
+	static const u8 padding = 0x1;
+	struct hctr2_request_ctx *rctx = skcipher_request_ctx(req);
+	struct polyval_ctx *poly_ctx = &rctx->u.poly_ctx;
+	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
+	struct sg_mapping_iter miter;
+	int i;
+	int n = 0;
+
+	sg_miter_start(&miter, sgl, sg_nents(sgl),
+		       SG_MITER_FROM_SG | SG_MITER_ATOMIC);
+	for (i = 0; i < bulk_len; i += n) {
+		sg_miter_next(&miter);
+		n = min_t(unsigned int, miter.length, bulk_len - i);
+		polyval_update(poly_ctx, miter.addr, n);
+	}
+	sg_miter_stop(&miter);
+
+	if (req->cryptlen % BLOCKCIPHER_BLOCK_SIZE)
+		polyval_update(poly_ctx, &padding, 1);
+	polyval_final(poly_ctx, digest);
+}
+
+static int hctr2_finish(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+	struct hctr2_request_ctx *rctx = skcipher_request_ctx(req);
+	struct polyval_ctx *poly_ctx = &rctx->u.poly_ctx;
+	u8 digest[POLYVAL_DIGEST_SIZE];
+
+	// U = UU ^ H(T || V)
+	// or M = MM ^ H(T || N)
+	polyval_import_blkaligned(poly_ctx, &tctx->poly_key,
+				  &rctx->hashed_tweak);
+	hctr2_hash_message(req, rctx->bulk_part_dst, digest);
+	crypto_xor(rctx->first_block, digest, BLOCKCIPHER_BLOCK_SIZE);
+
+	// Copy U (or M) into dst scatterlist
+	scatterwalk_map_and_copy(rctx->first_block, req->dst,
+				 0, BLOCKCIPHER_BLOCK_SIZE, 1);
+	return 0;
+}
+
+static void hctr2_xctr_done(void *data, int err)
+{
+	struct skcipher_request *req = data;
+
+	if (!err)
+		err = hctr2_finish(req);
+
+	skcipher_request_complete(req, err);
+}
+
+static int hctr2_crypt(struct skcipher_request *req, bool enc)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+	struct hctr2_request_ctx *rctx = skcipher_request_ctx(req);
+	u8 digest[POLYVAL_DIGEST_SIZE];
+	int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
+
+	// Requests must be at least one block
+	if (req->cryptlen < BLOCKCIPHER_BLOCK_SIZE)
+		return -EINVAL;
+
+	// Copy M (or U) into a temporary buffer
+	scatterwalk_map_and_copy(rctx->first_block, req->src,
+				 0, BLOCKCIPHER_BLOCK_SIZE, 0);
+
+	// Create scatterlists for N and V
+	rctx->bulk_part_src = scatterwalk_ffwd(rctx->sg_src, req->src,
+					       BLOCKCIPHER_BLOCK_SIZE);
+	rctx->bulk_part_dst = scatterwalk_ffwd(rctx->sg_dst, req->dst,
+					       BLOCKCIPHER_BLOCK_SIZE);
+
+	// MM = M ^ H(T || N)
+	// or UU = U ^ H(T || V)
+	hctr2_hash_tweak(req);
+	hctr2_hash_message(req, rctx->bulk_part_src, digest);
+	crypto_xor(digest, rctx->first_block, BLOCKCIPHER_BLOCK_SIZE);
+
+	// UU = E(MM)
+	// or MM = D(UU)
+	if (enc)
+		crypto_cipher_encrypt_one(tctx->blockcipher, rctx->first_block,
+					  digest);
+	else
+		crypto_cipher_decrypt_one(tctx->blockcipher, rctx->first_block,
+					  digest);
+
+	// S = MM ^ UU ^ L
+	crypto_xor(digest, rctx->first_block, BLOCKCIPHER_BLOCK_SIZE);
+	crypto_xor_cpy(rctx->xctr_iv, digest, tctx->L, BLOCKCIPHER_BLOCK_SIZE);
+
+	// V = XCTR(S, N)
+	// or N = XCTR(S, V)
+	skcipher_request_set_tfm(&rctx->u.xctr_req, tctx->xctr);
+	skcipher_request_set_crypt(&rctx->u.xctr_req, rctx->bulk_part_src,
+				   rctx->bulk_part_dst, bulk_len,
+				   rctx->xctr_iv);
+	skcipher_request_set_callback(&rctx->u.xctr_req,
+				      req->base.flags,
+				      hctr2_xctr_done, req);
+	return crypto_skcipher_encrypt(&rctx->u.xctr_req) ?:
+		hctr2_finish(req);
+}
+
+static int hctr2_encrypt(struct skcipher_request *req)
+{
+	return hctr2_crypt(req, true);
+}
+
+static int hctr2_decrypt(struct skcipher_request *req)
+{
+	return hctr2_crypt(req, false);
+}
+
+static int hctr2_init_tfm(struct crypto_skcipher *tfm)
+{
+	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
+	struct hctr2_instance_ctx *ictx = skcipher_instance_ctx(inst);
+	struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+	struct crypto_skcipher *xctr;
+	struct crypto_cipher *blockcipher;
+	int err;
+
+	xctr = crypto_spawn_skcipher(&ictx->xctr_spawn);
+	if (IS_ERR(xctr))
+		return PTR_ERR(xctr);
+
+	blockcipher = crypto_spawn_cipher(&ictx->blockcipher_spawn);
+	if (IS_ERR(blockcipher)) {
+		err = PTR_ERR(blockcipher);
+		goto err_free_xctr;
+	}
+
+	tctx->xctr = xctr;
+	tctx->blockcipher = blockcipher;
+
+	BUILD_BUG_ON(offsetofend(struct hctr2_request_ctx, u) !=
+				 sizeof(struct hctr2_request_ctx));
+	crypto_skcipher_set_reqsize(
+		tfm, max(sizeof(struct hctr2_request_ctx),
+			 offsetofend(struct hctr2_request_ctx, u.xctr_req) +
+				 crypto_skcipher_reqsize(xctr)));
+	return 0;
+
+err_free_xctr:
+	crypto_free_skcipher(xctr);
+	return err;
+}
+
+static void hctr2_exit_tfm(struct crypto_skcipher *tfm)
+{
+	struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
+
+	crypto_free_cipher(tctx->blockcipher);
+	crypto_free_skcipher(tctx->xctr);
+}
+
+static void hctr2_free_instance(struct skcipher_instance *inst)
+{
+	struct hctr2_instance_ctx *ictx = skcipher_instance_ctx(inst);
+
+	crypto_drop_cipher(&ictx->blockcipher_spawn);
+	crypto_drop_skcipher(&ictx->xctr_spawn);
+	kfree(inst);
+}
+
+static int hctr2_create_common(struct crypto_template *tmpl, struct rtattr **tb,
+			       const char *xctr_name)
+{
+	struct skcipher_alg_common *xctr_alg;
+	u32 mask;
+	struct skcipher_instance *inst;
+	struct hctr2_instance_ctx *ictx;
+	struct crypto_alg *blockcipher_alg;
+	char blockcipher_name[CRYPTO_MAX_ALG_NAME];
+	int len;
+	int err;
+
+	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
+	if (err)
+		return err;
+
+	inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+	ictx = skcipher_instance_ctx(inst);
+
+	/* Stream cipher, xctr(block_cipher) */
+	err = crypto_grab_skcipher(&ictx->xctr_spawn,
+				   skcipher_crypto_instance(inst),
+				   xctr_name, 0, mask);
+	if (err)
+		goto err_free_inst;
+	xctr_alg = crypto_spawn_skcipher_alg_common(&ictx->xctr_spawn);
+
+	err = -EINVAL;
+	if (strncmp(xctr_alg->base.cra_name, "xctr(", 5))
+		goto err_free_inst;
+	len = strscpy(blockcipher_name, xctr_alg->base.cra_name + 5);
+	if (len < 1)
+		goto err_free_inst;
+	if (blockcipher_name[len - 1] != ')')
+		goto err_free_inst;
+	blockcipher_name[len - 1] = 0;
+
+	/* Block cipher, e.g. "aes" */
+	err = crypto_grab_cipher(&ictx->blockcipher_spawn,
+				 skcipher_crypto_instance(inst),
+				 blockcipher_name, 0, mask);
+	if (err)
+		goto err_free_inst;
+	blockcipher_alg = crypto_spawn_cipher_alg(&ictx->blockcipher_spawn);
+
+	/* Require blocksize of 16 bytes */
+	err = -EINVAL;
+	if (blockcipher_alg->cra_blocksize != BLOCKCIPHER_BLOCK_SIZE)
+		goto err_free_inst;
+
+	/* Instance fields */
+
+	err = -ENAMETOOLONG;
+	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME, "hctr2(%s)",
+		     blockcipher_alg->cra_name) >= CRYPTO_MAX_ALG_NAME)
+		goto err_free_inst;
+	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
+		     "hctr2_base(%s,polyval-lib)",
+		     xctr_alg->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
+		goto err_free_inst;
+
+	inst->alg.base.cra_blocksize = BLOCKCIPHER_BLOCK_SIZE;
+	inst->alg.base.cra_ctxsize = sizeof(struct hctr2_tfm_ctx);
+	inst->alg.base.cra_alignmask = xctr_alg->base.cra_alignmask;
+	inst->alg.base.cra_priority = (2 * xctr_alg->base.cra_priority +
+				       blockcipher_alg->cra_priority) /
+				      3;
+
+	inst->alg.setkey = hctr2_setkey;
+	inst->alg.encrypt = hctr2_encrypt;
+	inst->alg.decrypt = hctr2_decrypt;
+	inst->alg.init = hctr2_init_tfm;
+	inst->alg.exit = hctr2_exit_tfm;
+	inst->alg.min_keysize = xctr_alg->min_keysize;
+	inst->alg.max_keysize = xctr_alg->max_keysize;
+	inst->alg.ivsize = TWEAK_SIZE;
+
+	inst->free = hctr2_free_instance;
+
+	err = skcipher_register_instance(tmpl, inst);
+	if (err) {
+err_free_inst:
+		hctr2_free_instance(inst);
+	}
+	return err;
+}
+
+static int hctr2_create_base(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	const char *xctr_name;
+	const char *polyval_name;
+
+	xctr_name = crypto_attr_alg_name(tb[1]);
+	if (IS_ERR(xctr_name))
+		return PTR_ERR(xctr_name);
+
+	polyval_name = crypto_attr_alg_name(tb[2]);
+	if (IS_ERR(polyval_name))
+		return PTR_ERR(polyval_name);
+	if (strcmp(polyval_name, "polyval") != 0 &&
+	    strcmp(polyval_name, "polyval-lib") != 0)
+		return -ENOENT;
+
+	return hctr2_create_common(tmpl, tb, xctr_name);
+}
+
+static int hctr2_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	const char *blockcipher_name;
+	char xctr_name[CRYPTO_MAX_ALG_NAME];
+
+	blockcipher_name = crypto_attr_alg_name(tb[1]);
+	if (IS_ERR(blockcipher_name))
+		return PTR_ERR(blockcipher_name);
+
+	if (snprintf(xctr_name, CRYPTO_MAX_ALG_NAME, "xctr(%s)",
+		    blockcipher_name) >= CRYPTO_MAX_ALG_NAME)
+		return -ENAMETOOLONG;
+
+	return hctr2_create_common(tmpl, tb, xctr_name);
+}
+
+static struct crypto_template hctr2_tmpls[] = {
+	{
+		/* hctr2_base(xctr_name, polyval_name) */
+		.name = "hctr2_base",
+		.create = hctr2_create_base,
+		.module = THIS_MODULE,
+	}, {
+		/* hctr2(blockcipher_name) */
+		.name = "hctr2",
+		.create = hctr2_create,
+		.module = THIS_MODULE,
+	}
+};
+
+static int __init hctr2_module_init(void)
+{
+	return crypto_register_templates(hctr2_tmpls, ARRAY_SIZE(hctr2_tmpls));
+}
+
+static void __exit hctr2_module_exit(void)
+{
+	return crypto_unregister_templates(hctr2_tmpls,
+					   ARRAY_SIZE(hctr2_tmpls));
+}
+
+module_init(hctr2_module_init);
+module_exit(hctr2_module_exit);
+
+MODULE_DESCRIPTION("HCTR2 length-preserving encryption mode");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS_CRYPTO("hctr2");
+MODULE_IMPORT_NS("CRYPTO_INTERNAL");