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, 185 insertions, 0 deletions

diff --git a/lib/base64.c b/lib/base64.c
new file mode 100644
index 000000000..325c7332b
--- /dev/null
+++ b/lib/base64.c
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * base64.c - Base64 with support for multiple variants
+ *
+ * Copyright (c) 2020 Hannes Reinecke, SUSE
+ *
+ * Based on the base64url routines from fs/crypto/fname.c
+ * (which are using the URL-safe Base64 encoding),
+ * modified to support multiple Base64 variants.
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/export.h>
+#include <linux/string.h>
+#include <linux/base64.h>
+
+static const char base64_tables[][65] = {
+	[BASE64_STD] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+	[BASE64_URLSAFE] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
+	[BASE64_IMAP] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,",
+};
+
+/*
+ * Initialize the base64 reverse mapping for a single character
+ * This macro maps a character to its corresponding base64 value,
+ * returning -1 if the character is invalid.
+ * char 'A'-'Z' maps to 0-25, 'a'-'z' maps to 26-51, '0'-'9' maps to 52-61,
+ * ch_62 maps to 62, ch_63 maps to 63, and other characters return -1
+ */
+#define INIT_1(v, ch_62, ch_63) \
+	[v] = (v) >= 'A' && (v) <= 'Z' ? (v) - 'A' \
+		: (v) >= 'a' && (v) <= 'z' ? (v) - 'a' + 26 \
+		: (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \
+		: (v) == (ch_62) ? 62 : (v) == (ch_63) ? 63 : -1
+
+/*
+ * Recursive macros to generate multiple Base64 reverse mapping table entries.
+ * Each macro generates a sequence of entries in the lookup table:
+ * INIT_2 generates 2 entries, INIT_4 generates 4, INIT_8 generates 8, and so on up to INIT_32.
+ */
+#define INIT_2(v, ...) INIT_1(v, __VA_ARGS__), INIT_1((v) + 1, __VA_ARGS__)
+#define INIT_4(v, ...) INIT_2(v, __VA_ARGS__), INIT_2((v) + 2, __VA_ARGS__)
+#define INIT_8(v, ...) INIT_4(v, __VA_ARGS__), INIT_4((v) + 4, __VA_ARGS__)
+#define INIT_16(v, ...) INIT_8(v, __VA_ARGS__), INIT_8((v) + 8, __VA_ARGS__)
+#define INIT_32(v, ...) INIT_16(v, __VA_ARGS__), INIT_16((v) + 16, __VA_ARGS__)
+
+#define BASE64_REV_INIT(ch_62, ch_63) { \
+	[0 ... 0x1f] = -1, \
+	INIT_32(0x20, ch_62, ch_63), \
+	INIT_32(0x40, ch_62, ch_63), \
+	INIT_32(0x60, ch_62, ch_63), \
+	[0x80 ... 0xff] = -1 }
+
+static const s8 base64_rev_maps[][256] = {
+	[BASE64_STD] = BASE64_REV_INIT('+', '/'),
+	[BASE64_URLSAFE] = BASE64_REV_INIT('-', '_'),
+	[BASE64_IMAP] = BASE64_REV_INIT('+', ',')
+};
+
+#undef BASE64_REV_INIT
+#undef INIT_32
+#undef INIT_16
+#undef INIT_8
+#undef INIT_4
+#undef INIT_2
+#undef INIT_1
+/**
+ * base64_encode() - Base64-encode some binary data
+ * @src: the binary data to encode
+ * @srclen: the length of @src in bytes
+ * @dst: (output) the Base64-encoded string.  Not NUL-terminated.
+ * @padding: whether to append '=' padding characters
+ * @variant: which base64 variant to use
+ *
+ * Encodes data using the selected Base64 variant.
+ *
+ * Return: the length of the resulting Base64-encoded string in bytes.
+ */
+int base64_encode(const u8 *src, int srclen, char *dst, bool padding, enum base64_variant variant)
+{
+	u32 ac = 0;
+	char *cp = dst;
+	const char *base64_table = base64_tables[variant];
+
+	while (srclen >= 3) {
+		ac = src[0] << 16 | src[1] << 8 | src[2];
+		*cp++ = base64_table[ac >> 18];
+		*cp++ = base64_table[(ac >> 12) & 0x3f];
+		*cp++ = base64_table[(ac >> 6) & 0x3f];
+		*cp++ = base64_table[ac & 0x3f];
+
+		src += 3;
+		srclen -= 3;
+	}
+
+	switch (srclen) {
+	case 2:
+		ac = src[0] << 16 | src[1] << 8;
+		*cp++ = base64_table[ac >> 18];
+		*cp++ = base64_table[(ac >> 12) & 0x3f];
+		*cp++ = base64_table[(ac >> 6) & 0x3f];
+		if (padding)
+			*cp++ = '=';
+		break;
+	case 1:
+		ac = src[0] << 16;
+		*cp++ = base64_table[ac >> 18];
+		*cp++ = base64_table[(ac >> 12) & 0x3f];
+		if (padding) {
+			*cp++ = '=';
+			*cp++ = '=';
+		}
+		break;
+	}
+	return cp - dst;
+}
+EXPORT_SYMBOL_GPL(base64_encode);
+
+/**
+ * base64_decode() - Base64-decode a string
+ * @src: the string to decode.  Doesn't need to be NUL-terminated.
+ * @srclen: the length of @src in bytes
+ * @dst: (output) the decoded binary data
+ * @padding: whether the input is expected to include '=' padding characters
+ * @variant: which base64 variant to use
+ *
+ * Decodes a string using the selected Base64 variant.
+ *
+ * Return: the length of the resulting decoded binary data in bytes,
+ *	   or -1 if the string isn't a valid Base64 string.
+ */
+int base64_decode(const char *src, int srclen, u8 *dst, bool padding, enum base64_variant variant)
+{
+	u8 *bp = dst;
+	s8 input[4];
+	s32 val;
+	const u8 *s = (const u8 *)src;
+	const s8 *base64_rev_tables = base64_rev_maps[variant];
+
+	while (srclen >= 4) {
+		input[0] = base64_rev_tables[s[0]];
+		input[1] = base64_rev_tables[s[1]];
+		input[2] = base64_rev_tables[s[2]];
+		input[3] = base64_rev_tables[s[3]];
+
+		val = input[0] << 18 | input[1] << 12 | input[2] << 6 | input[3];
+
+		if (unlikely(val < 0)) {
+			if (!padding || srclen != 4 || s[3] != '=')
+				return -1;
+			padding = 0;
+			srclen = s[2] == '=' ? 2 : 3;
+			break;
+		}
+
+		*bp++ = val >> 16;
+		*bp++ = val >> 8;
+		*bp++ = val;
+
+		s += 4;
+		srclen -= 4;
+	}
+
+	if (likely(!srclen))
+		return bp - dst;
+	if (padding || srclen == 1)
+		return -1;
+
+	val = (base64_rev_tables[s[0]] << 12) | (base64_rev_tables[s[1]] << 6);
+
+	if (srclen == 2) {
+		if (val & 0x800003ff)
+			return -1;
+		*bp++ = val >> 10;
+	} else {
+		val |= base64_rev_tables[s[2]];
+		if (val & 0x80000003)
+			return -1;
+		*bp++ = val >> 10;
+		*bp++ = val >> 2;
+	}
+	return bp - dst;
+}
+EXPORT_SYMBOL_GPL(base64_decode);