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, 159 insertions, 0 deletions

diff --git a/lib/crypto/blake2s.c b/lib/crypto/blake2s.c
new file mode 100644
index 000000000..71578a084
--- /dev/null
+++ b/lib/crypto/blake2s.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This is an implementation of the BLAKE2s hash and PRF functions.
+ *
+ * Information: https://blake2.net/
+ *
+ */
+
+#include <crypto/blake2s.h>
+#include <linux/bug.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/unroll.h>
+#include <linux/types.h>
+
+static const u8 blake2s_sigma[10][16] = {
+	{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
+	{ 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 },
+	{ 11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4 },
+	{ 7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8 },
+	{ 9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13 },
+	{ 2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9 },
+	{ 12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11 },
+	{ 13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10 },
+	{ 6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5 },
+	{ 10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0 },
+};
+
+static inline void blake2s_increment_counter(struct blake2s_ctx *ctx, u32 inc)
+{
+	ctx->t[0] += inc;
+	ctx->t[1] += (ctx->t[0] < inc);
+}
+
+static void __maybe_unused
+blake2s_compress_generic(struct blake2s_ctx *ctx,
+			 const u8 *data, size_t nblocks, u32 inc)
+{
+	u32 m[16];
+	u32 v[16];
+	int i;
+
+	WARN_ON(IS_ENABLED(DEBUG) &&
+		(nblocks > 1 && inc != BLAKE2S_BLOCK_SIZE));
+
+	while (nblocks > 0) {
+		blake2s_increment_counter(ctx, inc);
+		memcpy(m, data, BLAKE2S_BLOCK_SIZE);
+		le32_to_cpu_array(m, ARRAY_SIZE(m));
+		memcpy(v, ctx->h, 32);
+		v[ 8] = BLAKE2S_IV0;
+		v[ 9] = BLAKE2S_IV1;
+		v[10] = BLAKE2S_IV2;
+		v[11] = BLAKE2S_IV3;
+		v[12] = BLAKE2S_IV4 ^ ctx->t[0];
+		v[13] = BLAKE2S_IV5 ^ ctx->t[1];
+		v[14] = BLAKE2S_IV6 ^ ctx->f[0];
+		v[15] = BLAKE2S_IV7 ^ ctx->f[1];
+
+#define G(r, i, a, b, c, d) do { \
+	a += b + m[blake2s_sigma[r][2 * i + 0]]; \
+	d = ror32(d ^ a, 16); \
+	c += d; \
+	b = ror32(b ^ c, 12); \
+	a += b + m[blake2s_sigma[r][2 * i + 1]]; \
+	d = ror32(d ^ a, 8); \
+	c += d; \
+	b = ror32(b ^ c, 7); \
+} while (0)
+
+		/*
+		 * Unroll the rounds loop to enable constant-folding of the
+		 * blake2s_sigma values.
+		 */
+		unrolled_full
+		for (int r = 0; r < 10; r++) {
+			G(r, 0, v[0], v[4], v[8], v[12]);
+			G(r, 1, v[1], v[5], v[9], v[13]);
+			G(r, 2, v[2], v[6], v[10], v[14]);
+			G(r, 3, v[3], v[7], v[11], v[15]);
+			G(r, 4, v[0], v[5], v[10], v[15]);
+			G(r, 5, v[1], v[6], v[11], v[12]);
+			G(r, 6, v[2], v[7], v[8], v[13]);
+			G(r, 7, v[3], v[4], v[9], v[14]);
+		}
+#undef G
+
+		for (i = 0; i < 8; ++i)
+			ctx->h[i] ^= v[i] ^ v[i + 8];
+
+		data += BLAKE2S_BLOCK_SIZE;
+		--nblocks;
+	}
+}
+
+#ifdef CONFIG_CRYPTO_LIB_BLAKE2S_ARCH
+#include "blake2s.h" /* $(SRCARCH)/blake2s.h */
+#else
+#define blake2s_compress blake2s_compress_generic
+#endif
+
+static inline void blake2s_set_lastblock(struct blake2s_ctx *ctx)
+{
+	ctx->f[0] = -1;
+}
+
+void blake2s_update(struct blake2s_ctx *ctx, const u8 *in, size_t inlen)
+{
+	const size_t fill = BLAKE2S_BLOCK_SIZE - ctx->buflen;
+
+	if (unlikely(!inlen))
+		return;
+	if (inlen > fill) {
+		memcpy(ctx->buf + ctx->buflen, in, fill);
+		blake2s_compress(ctx, ctx->buf, 1, BLAKE2S_BLOCK_SIZE);
+		ctx->buflen = 0;
+		in += fill;
+		inlen -= fill;
+	}
+	if (inlen > BLAKE2S_BLOCK_SIZE) {
+		const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_SIZE);
+
+		blake2s_compress(ctx, in, nblocks - 1, BLAKE2S_BLOCK_SIZE);
+		in += BLAKE2S_BLOCK_SIZE * (nblocks - 1);
+		inlen -= BLAKE2S_BLOCK_SIZE * (nblocks - 1);
+	}
+	memcpy(ctx->buf + ctx->buflen, in, inlen);
+	ctx->buflen += inlen;
+}
+EXPORT_SYMBOL(blake2s_update);
+
+void blake2s_final(struct blake2s_ctx *ctx, u8 *out)
+{
+	WARN_ON(IS_ENABLED(DEBUG) && !out);
+	blake2s_set_lastblock(ctx);
+	memset(ctx->buf + ctx->buflen, 0,
+	       BLAKE2S_BLOCK_SIZE - ctx->buflen); /* Padding */
+	blake2s_compress(ctx, ctx->buf, 1, ctx->buflen);
+	cpu_to_le32_array(ctx->h, ARRAY_SIZE(ctx->h));
+	memcpy(out, ctx->h, ctx->outlen);
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL(blake2s_final);
+
+#ifdef blake2s_mod_init_arch
+static int __init blake2s_mod_init(void)
+{
+	blake2s_mod_init_arch();
+	return 0;
+}
+subsys_initcall(blake2s_mod_init);
+#endif
+
+MODULE_DESCRIPTION("BLAKE2s hash function");
+MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");