Ensure we test all parameters for BN_FLG_CONSTTIME

[openssl.git] / crypto / bn / bn_exp.c

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 25c05fadbadbcb2607c5f77e547e459e0c1f8cd4..f9353aaae0dc4eeb01947072210b438437b94706 100644 (file)
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2017 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -43,17 +43,15 @@ int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
     int i, bits, ret = 0;
     BIGNUM *v, *rr;
 
-    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
+    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(a, BN_FLG_CONSTTIME) != 0) {
         /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
         BNerr(BN_F_BN_EXP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
-        return -1;
+        return 0;
     }
 
     BN_CTX_start(ctx);
-    if ((r == a) || (r == p))
-        rr = BN_CTX_get(ctx);
-    else
-        rr = r;
+    rr = ((r == a) || (r == p)) ? BN_CTX_get(ctx) : r;
     v = BN_CTX_get(ctx);
     if (rr == NULL || v == NULL)
         goto err;
@@ -78,13 +76,14 @@ int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                 goto err;
         }
     }
-    if (r != rr)
-        BN_copy(r, rr);
+    if (r != rr && BN_copy(r, rr) == NULL)
+        goto err;
+
     ret = 1;
  err:
     BN_CTX_end(ctx);
     bn_check_top(r);
-    return (ret);
+    return ret;
 }
 
 int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
@@ -97,7 +96,7 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
     bn_check_top(m);
 
     /*-
-     * For even modulus  m = 2^k*m_odd,  it might make sense to compute
+     * For even modulus  m = 2^k*m_odd, it might make sense to compute
      * a^p mod m_odd  and  a^p mod 2^k  separately (with Montgomery
      * exponentiation for the odd part), using appropriate exponent
      * reductions, and combine the results using the CRT.
@@ -132,17 +131,12 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
 #define RECP_MUL_MOD
 
 #ifdef MONT_MUL_MOD
-    /*
-     * I have finally been able to take out this pre-condition of the top bit
-     * being set.  It was caused by an error in BN_div with negatives.  There
-     * was also another problem when for a^b%m a >= m.  eay 07-May-97
-     */
-    /* if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */
-
     if (BN_is_odd(m)) {
 # ifdef MONT_EXP_WORD
         if (a->top == 1 && !a->neg
-            && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)) {
+            && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)
+            && (BN_get_flags(a, BN_FLG_CONSTTIME) == 0)
+            && (BN_get_flags(m, BN_FLG_CONSTTIME) == 0)) {
             BN_ULONG A = a->d[0];
             ret = BN_mod_exp_mont_word(r, A, p, m, ctx, NULL);
         } else
@@ -174,10 +168,12 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     BIGNUM *val[TABLE_SIZE];
     BN_RECP_CTX recp;
 
-    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
+    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
         /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
         BNerr(BN_F_BN_MOD_EXP_RECP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
-        return -1;
+        return 0;
     }
 
     bits = BN_num_bits(p);
@@ -195,7 +191,7 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     BN_CTX_start(ctx);
     aa = BN_CTX_get(ctx);
     val[0] = BN_CTX_get(ctx);
-    if (!aa || !val[0])
+    if (val[0] == NULL)
         goto err;
 
     BN_RECP_CTX_init(&recp);
@@ -308,7 +304,9 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
     BIGNUM *val[TABLE_SIZE];
     BN_MONT_CTX *mont = NULL;
 
-    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
+    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
         return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
     }
 
@@ -336,7 +334,7 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
     d = BN_CTX_get(ctx);
     r = BN_CTX_get(ctx);
     val[0] = BN_CTX_get(ctx);
-    if (!d || !r || !val[0])
+    if (val[0] == NULL)
         goto err;
 
     /*
@@ -527,6 +525,14 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
 {
     int i, j;
     int width = 1 << window;
+    /*
+     * We declare table 'volatile' in order to discourage compiler
+     * from reordering loads from the table. Concern is that if
+     * reordered in specific manner loads might give away the
+     * information we are trying to conceal. Some would argue that
+     * compiler can reorder them anyway, but it can as well be
+     * argued that doing so would be violation of standard...
+     */
     volatile BN_ULONG *table = (volatile BN_ULONG *)buf;
 
     if (bn_wexpand(b, top) == NULL)
@@ -1093,7 +1099,7 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
     int b, bits, ret = 0;
     int r_is_one;
     BN_ULONG w, next_w;
-    BIGNUM *d, *r, *t;
+    BIGNUM *r, *t;
     BIGNUM *swap_tmp;
 #define BN_MOD_MUL_WORD(r, w, m) \
                 (BN_mul_word(r, (w)) && \
@@ -1112,10 +1118,11 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
                 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
 
-    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
+    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
         /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
         BNerr(BN_F_BN_MOD_EXP_MONT_WORD, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
-        return -1;
+        return 0;
     }
 
     bn_check_top(p);
@@ -1146,10 +1153,9 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
     }
 
     BN_CTX_start(ctx);
-    d = BN_CTX_get(ctx);
     r = BN_CTX_get(ctx);
     t = BN_CTX_get(ctx);
-    if (d == NULL || r == NULL || t == NULL)
+    if (t == NULL)
         goto err;
 
     if (in_mont != NULL)
@@ -1243,10 +1249,12 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     /* Table of variables obtained from 'ctx' */
     BIGNUM *val[TABLE_SIZE];
 
-    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
+    if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
+            || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
         /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
         BNerr(BN_F_BN_MOD_EXP_SIMPLE, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
-        return -1;
+        return 0;
     }
 
     bits = BN_num_bits(p);
@@ -1264,7 +1272,7 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
     BN_CTX_start(ctx);
     d = BN_CTX_get(ctx);
     val[0] = BN_CTX_get(ctx);
-    if (!d || !val[0])
+    if (val[0] == NULL)
         goto err;
 
     if (!BN_nnmod(val[0], a, m, ctx))