initial commit, 4.5 stable

thirdparty/mbedtls/library/constant_time.c

@@ -0,0 +1,248 @@
+/**
+ *  Constant-time functions
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+/*
+ * The following functions are implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+
+#include <stdint.h>
+#include <limits.h>
+
+#include "common.h"
+#include "constant_time_internal.h"
+#include "mbedtls/constant_time.h"
+#include "mbedtls/error.h"
+#include "mbedtls/platform_util.h"
+
+#include <string.h>
+
+#if !defined(MBEDTLS_CT_ASM)
+/*
+ * Define an object with the value zero, such that the compiler cannot prove that it
+ * has the value zero (because it is volatile, it "may be modified in ways unknown to
+ * the implementation").
+ */
+volatile mbedtls_ct_uint_t mbedtls_ct_zero = 0;
+#endif
+
+/*
+ * Define MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS where assembly is present to
+ * perform fast unaligned access to volatile data.
+ *
+ * This is needed because mbedtls_get_unaligned_uintXX etc don't support volatile
+ * memory accesses.
+ *
+ * Some of these definitions could be moved into alignment.h but for now they are
+ * only used here.
+ */
+#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) && \
+    ((defined(MBEDTLS_CT_ARM_ASM) && (UINTPTR_MAX == 0xfffffffful)) || \
+    defined(MBEDTLS_CT_AARCH64_ASM))
+/* We check pointer sizes to avoid issues with them not matching register size requirements */
+#define MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS
+
+static inline uint32_t mbedtls_get_unaligned_volatile_uint32(volatile const unsigned char *p)
+{
+    /* This is UB, even where it's safe:
+     *    return *((volatile uint32_t*)p);
+     * so instead the same thing is expressed in assembly below.
+     */
+    uint32_t r;
+#if defined(MBEDTLS_CT_ARM_ASM)
+    asm volatile ("ldr %0, [%1]" : "=r" (r) : "r" (p) :);
+#elif defined(MBEDTLS_CT_AARCH64_ASM)
+    asm volatile ("ldr %w0, [%1]" : "=r" (r) : MBEDTLS_ASM_AARCH64_PTR_CONSTRAINT(p) :);
+#else
+#error "No assembly defined for mbedtls_get_unaligned_volatile_uint32"
+#endif
+    return r;
+}
+#endif /* defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) &&
+          (defined(MBEDTLS_CT_ARM_ASM) || defined(MBEDTLS_CT_AARCH64_ASM)) */
+
+int mbedtls_ct_memcmp(const void *a,
+                      const void *b,
+                      size_t n)
+{
+    size_t i = 0;
+    /*
+     * `A` and `B` are cast to volatile to ensure that the compiler
+     * generates code that always fully reads both buffers.
+     * Otherwise it could generate a test to exit early if `diff` has all
+     * bits set early in the loop.
+     */
+    volatile const unsigned char *A = (volatile const unsigned char *) a;
+    volatile const unsigned char *B = (volatile const unsigned char *) b;
+    uint32_t diff = 0;
+
+#if defined(MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS)
+    for (; (i + 4) <= n; i += 4) {
+        uint32_t x = mbedtls_get_unaligned_volatile_uint32(A + i);
+        uint32_t y = mbedtls_get_unaligned_volatile_uint32(B + i);
+        diff |= x ^ y;
+    }
+#endif
+
+    for (; i < n; i++) {
+        /* Read volatile data in order before computing diff.
+         * This avoids IAR compiler warning:
+         * 'the order of volatile accesses is undefined ..' */
+        unsigned char x = A[i], y = B[i];
+        diff |= x ^ y;
+    }
+
+
+#if (INT_MAX < INT32_MAX)
+    /* We don't support int smaller than 32-bits, but if someone tried to build
+     * with this configuration, there is a risk that, for differing data, the
+     * only bits set in diff are in the top 16-bits, and would be lost by a
+     * simple cast from uint32 to int.
+     * This would have significant security implications, so protect against it. */
+#error "mbedtls_ct_memcmp() requires minimum 32-bit ints"
+#else
+    /* The bit-twiddling ensures that when we cast uint32_t to int, we are casting
+     * a value that is in the range 0..INT_MAX - a value larger than this would
+     * result in implementation defined behaviour.
+     *
+     * This ensures that the value returned by the function is non-zero iff
+     * diff is non-zero.
+     */
+    return (int) ((diff & 0xffff) | (diff >> 16));
+#endif
+}
+
+#if defined(MBEDTLS_NIST_KW_C)
+
+int mbedtls_ct_memcmp_partial(const void *a,
+                              const void *b,
+                              size_t n,
+                              size_t skip_head,
+                              size_t skip_tail)
+{
+    unsigned int diff = 0;
+
+    volatile const unsigned char *A = (volatile const unsigned char *) a;
+    volatile const unsigned char *B = (volatile const unsigned char *) b;
+
+    size_t valid_end = n - skip_tail;
+
+    for (size_t i = 0; i < n; i++) {
+        unsigned char x = A[i], y = B[i];
+        unsigned int d = x ^ y;
+        mbedtls_ct_condition_t valid = mbedtls_ct_bool_and(mbedtls_ct_uint_ge(i, skip_head),
+                                                           mbedtls_ct_uint_lt(i, valid_end));
+        diff |= mbedtls_ct_uint_if_else_0(valid, d);
+    }
+
+    /* Since we go byte-by-byte, the only bits set will be in the bottom 8 bits, so the
+     * cast from uint to int is safe. */
+    return (int) diff;
+}
+
+#endif
+
+#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
+
+void mbedtls_ct_memmove_left(void *start, size_t total, size_t offset)
+{
+    volatile unsigned char *buf = start;
+    for (size_t i = 0; i < total; i++) {
+        mbedtls_ct_condition_t no_op = mbedtls_ct_uint_gt(total - offset, i);
+        /* The first `total - offset` passes are a no-op. The last
+         * `offset` passes shift the data one byte to the left and
+         * zero out the last byte. */
+        for (size_t n = 0; n < total - 1; n++) {
+            unsigned char current = buf[n];
+            unsigned char next    = buf[n+1];
+            buf[n] = mbedtls_ct_uint_if(no_op, current, next);
+        }
+        buf[total-1] = mbedtls_ct_uint_if_else_0(no_op, buf[total-1]);
+    }
+}
+
+#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */
+
+void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition,
+                          unsigned char *dest,
+                          const unsigned char *src1,
+                          const unsigned char *src2,
+                          size_t len)
+{
+#if defined(MBEDTLS_CT_SIZE_64)
+    const uint64_t mask     = (uint64_t) condition;
+    const uint64_t not_mask = (uint64_t) ~mbedtls_ct_compiler_opaque(condition);
+#else
+    const uint32_t mask     = (uint32_t) condition;
+    const uint32_t not_mask = (uint32_t) ~mbedtls_ct_compiler_opaque(condition);
+#endif
+
+    /* If src2 is NULL, setup src2 so that we read from the destination address.
+     *
+     * This means that if src2 == NULL && condition is false, the result will be a
+     * no-op because we read from dest and write the same data back into dest.
+     */
+    if (src2 == NULL) {
+        src2 = dest;
+    }
+
+    /* dest[i] = c1 == c2 ? src[i] : dest[i] */
+    size_t i = 0;
+#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS)
+#if defined(MBEDTLS_CT_SIZE_64)
+    for (; (i + 8) <= len; i += 8) {
+        uint64_t a = mbedtls_get_unaligned_uint64(src1 + i) & mask;
+        uint64_t b = mbedtls_get_unaligned_uint64(src2 + i) & not_mask;
+        mbedtls_put_unaligned_uint64(dest + i, a | b);
+    }
+#else
+    for (; (i + 4) <= len; i += 4) {
+        uint32_t a = mbedtls_get_unaligned_uint32(src1 + i) & mask;
+        uint32_t b = mbedtls_get_unaligned_uint32(src2 + i) & not_mask;
+        mbedtls_put_unaligned_uint32(dest + i, a | b);
+    }
+#endif /* defined(MBEDTLS_CT_SIZE_64) */
+#endif /* MBEDTLS_EFFICIENT_UNALIGNED_ACCESS */
+    for (; i < len; i++) {
+        dest[i] = (src1[i] & mask) | (src2[i] & not_mask);
+    }
+}
+
+void mbedtls_ct_memcpy_offset(unsigned char *dest,
+                              const unsigned char *src,
+                              size_t offset,
+                              size_t offset_min,
+                              size_t offset_max,
+                              size_t len)
+{
+    size_t offsetval;
+
+    for (offsetval = offset_min; offsetval <= offset_max; offsetval++) {
+        mbedtls_ct_memcpy_if(mbedtls_ct_uint_eq(offsetval, offset), dest, src + offsetval, NULL,
+                             len);
+    }
+}
+
+#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
+
+void mbedtls_ct_zeroize_if(mbedtls_ct_condition_t condition, void *buf, size_t len)
+{
+    uint32_t mask = (uint32_t) ~condition;
+    uint8_t *p = (uint8_t *) buf;
+    size_t i = 0;
+#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS)
+    for (; (i + 4) <= len; i += 4) {
+        mbedtls_put_unaligned_uint32((void *) (p + i),
+                                     mbedtls_get_unaligned_uint32((void *) (p + i)) & mask);
+    }
+#endif
+    for (; i < len; i++) {
+        p[i] = p[i] & mask;
+    }
+}
+
+#endif /* defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) */