update for constant time calculates

Patch largely from Dan Harkins

src/modules/rlm_eap/types/rlm_eap_pwd/const_time.h

@@ -0,0 +1,190 @@
+/*
+ * Helper functions for constant time operations
+ * Copyright (c) 2019, The Linux Foundation
+ *
+ * This software may be distributed under the terms of the BSD license.
+ * See README for more details.
+ *
+ * These helper functions can be used to implement logic that needs to minimize
+ * externally visible differences in execution path by avoiding use of branches,
+ * avoiding early termination or other time differences, and forcing same memory
+ * access pattern regardless of values.
+ */
+
+#ifndef CONST_TIME_H
+#define CONST_TIME_H
+
+
+#if defined(__clang__)
+#define NO_UBSAN_UINT_OVERFLOW                                        \
+	__attribute__((no_sanitize("unsigned-integer-overflow")))
+#else
+#define NO_UBSAN_UINT_OVERFLOW
+#endif
+
+/**
+ * const_time_fill_msb - Fill all bits with MSB value
+ * @val: Input value
+ * Returns: Value with all the bits set to the MSB of the input val
+ */
+static inline unsigned int const_time_fill_msb(unsigned int val)
+{
+	/* Move the MSB to LSB and multiple by -1 to fill in all bits. */
+	return (val >> (sizeof(val) * 8 - 1)) * ~0U;
+}
+
+
+/* Returns: -1 if val is zero; 0 if val is not zero */
+static inline unsigned int const_time_is_zero(unsigned int val)
+	NO_UBSAN_UINT_OVERFLOW
+{
+	/* Set MSB to 1 for 0 and fill rest of bits with the MSB value */
+	return const_time_fill_msb(~val & (val - 1));
+}
+
+
+/* Returns: -1 if a == b; 0 if a != b */
+static inline unsigned int const_time_eq(unsigned int a, unsigned int b)
+{
+	return const_time_is_zero(a ^ b);
+}
+
+
+/* Returns: -1 if a == b; 0 if a != b */
+static inline unsigned char const_time_eq_u8(unsigned int a, unsigned int b)
+{
+	return (unsigned char) const_time_eq(a, b);
+}
+
+
+/**
+ * const_time_eq_bin - Constant time memory comparison
+ * @a: First buffer to compare
+ * @b: Second buffer to compare
+ * @len: Number of octets to compare
+ * Returns: -1 if buffers are equal, 0 if not
+ *
+ * This function is meant for comparing passwords or hash values where
+ * difference in execution time or memory access pattern could provide external
+ * observer information about the location of the difference in the memory
+ * buffers. The return value does not behave like memcmp(), i.e.,
+ * const_time_eq_bin() cannot be used to sort items into a defined order. Unlike
+ * memcmp(), the execution time of const_time_eq_bin() does not depend on the
+ * contents of the compared memory buffers, but only on the total compared
+ * length.
+ */
+static inline unsigned int const_time_eq_bin(const void *a, const void *b,
+					     size_t len)
+{
+	const unsigned char *aa = a;
+	const unsigned char *bb = b;
+	size_t i;
+	unsigned char res = 0;
+
+	for (i = 0; i < len; i++)
+		res |= aa[i] ^ bb[i];
+
+	return const_time_is_zero(res);
+}
+
+
+/**
+ * const_time_select - Constant time unsigned int selection
+ * @mask: 0 (false) or -1 (true) to identify which value to select
+ * @true_val: Value to select for the true case
+ * @false_val: Value to select for the false case
+ * Returns: true_val if mask == -1, false_val if mask == 0
+ */
+static inline unsigned int const_time_select(unsigned int mask,
+					     unsigned int true_val,
+					     unsigned int false_val)
+{
+	return (mask & true_val) | (~mask & false_val);
+}
+
+
+/**
+ * const_time_select_int - Constant time int selection
+ * @mask: 0 (false) or -1 (true) to identify which value to select
+ * @true_val: Value to select for the true case
+ * @false_val: Value to select for the false case
+ * Returns: true_val if mask == -1, false_val if mask == 0
+ */
+static inline int const_time_select_int(unsigned int mask, int true_val,
+					int false_val)
+{
+	return (int) const_time_select(mask, (unsigned int) true_val,
+				       (unsigned int) false_val);
+}
+
+
+/**
+ * const_time_select_u8 - Constant time u8 selection
+ * @mask: 0 (false) or -1 (true) to identify which value to select
+ * @true_val: Value to select for the true case
+ * @false_val: Value to select for the false case
+ * Returns: true_val if mask == -1, false_val if mask == 0
+ */
+static inline unsigned char const_time_select_u8(unsigned char mask, unsigned char true_val, unsigned char false_val)
+{
+	return (unsigned char) const_time_select(mask, true_val, false_val);
+}
+
+
+/**
+ * const_time_select_s8 - Constant time s8 selection
+ * @mask: 0 (false) or -1 (true) to identify which value to select
+ * @true_val: Value to select for the true case
+ * @false_val: Value to select for the false case
+ * Returns: true_val if mask == -1, false_val if mask == 0
+ */
+static inline char const_time_select_s8(char mask, char true_val, char false_val)
+{
+	return (char) const_time_select(mask, (unsigned int) true_val,
+				      (unsigned int) false_val);
+}
+
+
+/**
+ * const_time_select_bin - Constant time binary buffer selection copy
+ * @mask: 0 (false) or -1 (true) to identify which value to copy
+ * @true_val: Buffer to copy for the true case
+ * @false_val: Buffer to copy for the false case
+ * @len: Number of octets to copy
+ * @dst: Destination buffer for the copy
+ *
+ * This function copies the specified buffer into the destination buffer using
+ * operations with identical memory access pattern regardless of which buffer
+ * is being copied.
+ */
+static inline void const_time_select_bin(unsigned char mask, const unsigned char *true_val,
+					 const unsigned char *false_val, size_t len,
+					 unsigned char *dst)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		dst[i] = const_time_select_u8(mask, true_val[i], false_val[i]);
+}
+
+
+static inline int const_time_memcmp(const void *a, const void *b, size_t len)
+{
+	const unsigned char *aa = a;
+	const unsigned char *bb = b;
+	int diff, res = 0;
+	unsigned int mask;
+
+	if (len == 0)
+		return 0;
+	do {
+		len--;
+		diff = (int) aa[len] - (int) bb[len];
+		mask = const_time_is_zero((unsigned int) diff);
+		res = const_time_select_int(mask, res, diff);
+	} while (len);
+
+	return res;
+}
+
+#endif /* CONST_TIME_H */