File 0001-crypto-bn-add-more-fixed-top-routines.patch of Package openssl

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File 0001-crypto-bn-add-more-fixed-top-routines.patch of Package openssl (Revision 5a88342563ffcbe6a98674a639f0e8fc)

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From 387d170b32ceeac450bfa50b81db9db9179dc880 Mon Sep 17 00:00:00 2001
From: Andy Polyakov <appro@openssl.org>
Date: Fri, 10 Aug 2018 19:31:22 +0200
Subject: [PATCH 1/4] crypto/bn: add more fixed-top routines.

Add bn_mul_fixed_top, bn_from_mont_fixed_top, bn_mod_sub_fixed_top.
Switch to bn_{mul|sqr}_fixed_top in bn_mul_mont_fixed_top and remove
memset in bn_from_montgomery_word.

(cherry picked from commit fcc4ee09473cac511eca90faa003661c7786e4f9)

Resolved conflicts:
	crypto/bn/bn_mod.c
	crypto/bn_int.h

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/6942)
---
 crypto/bn/bn_mod.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
 crypto/bn/bn_mont.c | 29 +++++++++++++-------
 crypto/bn/bn_mul.c  | 12 +++++++-
 crypto/bn/bn_sqr.c  | 12 +++++++-
 crypto/bn_int.h     |  6 ++++
 5 files changed, 113 insertions(+), 13 deletions(-)

Index: openssl-1.0.2j/crypto/bn/bn_mod.c
===================================================================
--- openssl-1.0.2j.orig/crypto/bn/bn_mod.c
+++ openssl-1.0.2j/crypto/bn/bn_mod.c
@@ -170,6 +170,70 @@ int BN_mod_sub(BIGNUM *r, const BIGNUM *
 }
 
 /*
+ * BN_mod_sub variant that may be used if both a and b are non-negative,
+ * a is less than m, while b is of same bit width as m. It's implemented
+ * as subtraction followed by two conditional additions.
+ *
+ * 0 <= a < m
+ * 0 <= b < 2^w < 2*m
+ *
+ * after subtraction
+ *
+ * -2*m < r = a - b < m
+ *
+ * Thus it takes up to two conditional additions to make |r| positive.
+ */
+int bn_mod_sub_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
+                         const BIGNUM *m)
+{
+    size_t i, ai, bi, mtop = m->top;
+    BN_ULONG borrow, carry, ta, tb, mask, *rp;
+    const BN_ULONG *ap, *bp;
+
+    if (bn_wexpand(r, m->top) == NULL)
+        return 0;
+
+    rp = r->d;
+    ap = a->d != NULL ? a->d : rp;
+    bp = b->d != NULL ? b->d : rp;
+
+    for (i = 0, ai = 0, bi = 0, borrow = 0; i < mtop;) {
+        mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
+        ta = ap[ai] & mask;
+
+        mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
+        tb = bp[bi] & mask;
+        rp[i] = ta - tb - borrow;
+        if (ta != tb)
+            borrow = (ta < tb);
+
+        i++;
+        ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
+        bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
+    }
+    ap = m->d;
+    for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
+        ta = ((ap[i] & mask) + carry) & BN_MASK2;
+        carry = (ta < carry);
+        rp[i] = (rp[i] + ta) & BN_MASK2;
+        carry += (rp[i] < ta);
+    }
+    borrow -= carry;
+    for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
+        ta = ((ap[i] & mask) + carry) & BN_MASK2;
+        carry = (ta < carry);
+        rp[i] = (rp[i] + ta) & BN_MASK2;
+        carry += (rp[i] < ta);
+    }
+
+    r->top = mtop;
+    r->flags |= BN_FLG_FIXED_TOP;
+    r->neg = 0;
+
+    return 1;
+}
+
+/*
  * BN_mod_sub variant that may be used if both a and b are non-negative and
  * less than m
  */
Index: openssl-1.0.2j/crypto/bn/bn_mont.c
===================================================================
--- openssl-1.0.2j.orig/crypto/bn/bn_mont.c
+++ openssl-1.0.2j/crypto/bn/bn_mont.c
@@ -153,10 +153,10 @@ int BN_mod_mul_montgomery(BIGNUM *r, con
 
     bn_check_top(tmp);
     if (a == b) {
-        if (!BN_sqr(tmp, a, ctx))
+        if (!bn_sqr_fixed_top(tmp, a, ctx))
             goto err;
     } else {
-        if (!BN_mul(tmp, a, b, ctx))
+        if (!bn_mul_fixed_top(tmp, a, b, ctx))
             goto err;
     }
     /* reduce from aRR to aR */
@@ -180,6 +180,7 @@ static int BN_from_montgomery_word(BIGNU
     BIGNUM *n;
     BN_ULONG *ap, *np, *rp, n0, v, carry;
     int nl, max, i;
+    unsigned int rtop;
 
     n = &(mont->N);
     nl = n->top;
@@ -197,12 +198,10 @@ static int BN_from_montgomery_word(BIGNU
     rp = r->d;
 
     /* clear the top words of T */
-# if 1
-    for (i = r->top; i < max; i++) /* memset? XXX */
-        rp[i] = 0;
-# else
-    memset(&(rp[r->top]), 0, (max - r->top) * sizeof(BN_ULONG));
-# endif
+    for (rtop = r->top, i = 0; i < max; i++) {
+        v = (BN_ULONG)0 - ((i - rtop) >> (8 * sizeof(rtop) - 1));
+        rp[i] &= v;
+    }
 
     r->top = max;
     n0 = mont->n0[0];
@@ -290,6 +289,18 @@ static int BN_from_montgomery_word(BIGNU
 int BN_from_montgomery(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
                        BN_CTX *ctx)
 {
+    int retn;
+
+    retn = bn_from_mont_fixed_top(ret, a, mont, ctx);
+    bn_correct_top(ret);
+    bn_check_top(ret);
+
+    return retn;
+}
+
+int bn_from_mont_fixed_top(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
+                           BN_CTX *ctx)
+{
     int retn = 0;
 #ifdef MONT_WORD
     BIGNUM *t;
Index: openssl-1.0.2j/crypto/bn/bn_mul.c
===================================================================
--- openssl-1.0.2j.orig/crypto/bn/bn_mul.c
+++ openssl-1.0.2j/crypto/bn/bn_mul.c
@@ -936,6 +936,16 @@ void bn_mul_high(BN_ULONG *r, BN_ULONG *
 
 int BN_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx)
 {
+    int ret = bn_mul_fixed_top(r, a, b, ctx);
+
+    bn_correct_top(r);
+    bn_check_top(r);
+
+    return ret;
+}
+
+int bn_mul_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx)
+{
     int ret = 0;
     int top, al, bl;
     BIGNUM *rr;
@@ -1082,7 +1092,7 @@ int BN_mul(BIGNUM *r, const BIGNUM *a, c
 #if defined(BN_MUL_COMBA) || defined(BN_RECURSION)
  end:
 #endif
-    bn_correct_top(rr);
+    rr->flags |= BN_FLG_FIXED_TOP;
     if (r != rr)
         BN_copy(r, rr);
     ret = 1;
Index: openssl-1.0.2j/crypto/bn/bn_sqr.c
===================================================================
--- openssl-1.0.2j.orig/crypto/bn/bn_sqr.c
+++ openssl-1.0.2j/crypto/bn/bn_sqr.c
@@ -66,6 +66,16 @@
  */
 int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
 {
+    int ret = bn_sqr_fixed_top(r, a, ctx);
+
+    bn_correct_top(r);
+    bn_check_top(r);
+
+    return ret;
+}
+
+int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
+{
     int max, al;
     int ret = 0;
     BIGNUM *tmp, *rr;
@@ -135,16 +145,11 @@ int BN_sqr(BIGNUM *r, const BIGNUM *a, B
     }
 
     rr->neg = 0;
-    /*
-     * If the most-significant half of the top word of 'a' is zero, then the
-     * square of 'a' will max-1 words.
-     */
-    if (a->d[al - 1] == (a->d[al - 1] & BN_MASK2l))
-        rr->top = max - 1;
-    else
-        rr->top = max;
-    if (rr != r)
-        BN_copy(r, rr);
+    rr->top = max;
+    rr->flags |= BN_FLG_FIXED_TOP;
+    if (r != rr && BN_copy(r, rr) == NULL)
+	goto err;
+
     ret = 1;
  err:
     bn_check_top(rr);
Index: openssl-1.0.2j/crypto/bn/bn.h
===================================================================
--- openssl-1.0.2j.orig/crypto/bn/bn.h
+++ openssl-1.0.2j/crypto/bn/bn.h
@@ -583,6 +583,12 @@ int BN_mod_mul_montgomery(BIGNUM *r, con
 int BN_from_montgomery(BIGNUM *r, const BIGNUM *a,
                        BN_MONT_CTX *mont, BN_CTX *ctx);
 int bn_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen);
+int bn_from_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont,
+			   BN_CTX *ctx);
+int bn_mod_sub_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
+                         const BIGNUM *m);
+int bn_mul_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
+int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx);
 void BN_MONT_CTX_free(BN_MONT_CTX *mont);
 int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx);
 BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from);
@@ -774,6 +780,16 @@ BIGNUM *bn_dup_expand(const BIGNUM *a, i
 /* We only need assert() when debugging */
 #  include <assert.h>
 
+/*
+ * The new BN_FLG_FIXED_TOP flag marks vectors that were not treated with
+ * bn_correct_top, in other words such vectors are permitted to have zeros
+ * in most significant limbs. Such vectors are used internally to achieve
+ * execution time invariance for critical operations with private keys.
+ * It's BN_DEBUG-only flag, because user application is not supposed to
+ * observe it anyway. Moreover, optimizing compiler would actually remove
+ * all operations manipulating the bit in question in non-BN_DEBUG build.
+ */
+#  define BN_FLG_FIXED_TOP 0x10000
 #  ifdef BN_DEBUG_RAND
 /* To avoid "make update" cvs wars due to BN_DEBUG, use some tricks */
 #   ifndef RAND_pseudo_bytes
@@ -807,7 +823,8 @@ int RAND_pseudo_bytes(unsigned char *buf
                 const BIGNUM *_bnum2 = (a); \
                 if (_bnum2 != NULL) { \
                         assert((_bnum2->top == 0) || \
-                                (_bnum2->d[_bnum2->top - 1] != 0)); \
+			        (_bnum2->flags & BN_FLG_FIXED_TOP) || \
+                               (_bnum2->d[_bnum2->top - 1] != 0)); \
                         bn_pollute(_bnum2); \
                 } \
         } while(0)
@@ -825,6 +842,7 @@ int RAND_pseudo_bytes(unsigned char *buf
 
 # else                          /* !BN_DEBUG */
 
+#  define BN_FLG_FIXED_TOP 0
 #  define bn_pollute(a)
 #  define bn_check_top(a)
 #  define bn_fix_top(a)           bn_correct_top(a)

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