1 files changed, 67 insertions, 173 deletions

diff --git a/src/lib/libcrypto/bn/bn_exp.c b/src/lib/libcrypto/bn/bn_exp.c
index 2abf6fd678..d9b6c737fc 100644
--- a/src/lib/libcrypto/bn/bn_exp.c
+++ b/src/lib/libcrypto/bn/bn_exp.c
@@ -113,18 +113,6 @@
 #include "cryptlib.h"
 #include "bn_lcl.h"
 
-#include <stdlib.h>
-#ifdef _WIN32
-# include <malloc.h>
-# ifndef alloca
-#  define alloca _alloca
-# endif
-#elif defined(__GNUC__)
-# ifndef alloca
-#  define alloca(s) __builtin_alloca((s))
-# endif
-#endif
-
 /* maximum precomputation table size for *variable* sliding windows */
 #define TABLE_SIZE      32
 
@@ -534,17 +522,23 @@ err:
  * as cache lines are concerned.  The following functions are used to transfer a BIGNUM
  * from/to that table. */
 
-static int MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top, unsigned char *buf, int idx, int width)
+static int MOD_EXP_CTIME_COPY_TO_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx, int width)
         {
         size_t i, j;
 
-        if (top > b->top)
-                top = b->top; /* this works because 'buf' is explicitly zeroed */
+        if (bn_wexpand(b, top) == NULL)
+                return 0;
+        while (b->top < top)
+                {
+                b->d[b->top++] = 0;
+                }
+        
         for (i = 0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
                 {
                 buf[j] = ((unsigned char*)b->d)[i];
                 }
 
+        bn_correct_top(b);
         return 1;
         }
 
@@ -567,7 +561,7 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf
 
 /* Given a pointer value, compute the next address that is a cache line multiple. */
 #define MOD_EXP_CTIME_ALIGN(x_) \
-        ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((size_t)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
+        ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((BN_ULONG)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
 
 /* This variant of BN_mod_exp_mont() uses fixed windows and the special
  * precomputation memory layout to limit data-dependency to a minimum
@@ -578,15 +572,17 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf
 int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
                     const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
         {
-        int i,bits,ret=0,window,wvalue;
+        int i,bits,ret=0,idx,window,wvalue;
         int top;
+        BIGNUM *r;
+        const BIGNUM *aa;
         BN_MONT_CTX *mont=NULL;
 
         int numPowers;
         unsigned char *powerbufFree=NULL;
         int powerbufLen = 0;
         unsigned char *powerbuf=NULL;
-        BIGNUM tmp, am;
+        BIGNUM *computeTemp=NULL, *am=NULL;
 
         bn_check_top(a);
         bn_check_top(p);
@@ -606,7 +602,10 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
                 return ret;
                 }
 
+        /* Initialize BIGNUM context and allocate intermediate result */
         BN_CTX_start(ctx);
+        r = BN_CTX_get(ctx);
+        if (r == NULL) goto err;
 
         /* Allocate a montgomery context if it was not supplied by the caller.
          * If this is not done, things will break in the montgomery part.
@@ -621,154 +620,40 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
 
         /* Get the window size to use with size of p. */
         window = BN_window_bits_for_ctime_exponent_size(bits);
-#if defined(OPENSSL_BN_ASM_MONT5)
-        if (window==6 && bits<=1024) window=5;  /* ~5% improvement of 2048-bit RSA sign */
-#endif
 
         /* Allocate a buffer large enough to hold all of the pre-computed
-         * powers of am, am itself and tmp.
+         * powers of a.
          */
         numPowers = 1 << window;
-        powerbufLen = sizeof(m->d[0])*(top*numPowers +
-                                ((2*top)>numPowers?(2*top):numPowers));
-#ifdef alloca
-        if (powerbufLen < 3072)
-                powerbufFree = alloca(powerbufLen+MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH);
-        else
-#endif
+        powerbufLen = sizeof(m->d[0])*top*numPowers;
         if ((powerbufFree=(unsigned char*)OPENSSL_malloc(powerbufLen+MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH)) == NULL)
                 goto err;
                 
         powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
         memset(powerbuf, 0, powerbufLen);
 
-#ifdef alloca
-        if (powerbufLen < 3072)
-                powerbufFree = NULL;
-#endif
+        /* Initialize the intermediate result. Do this early to save double conversion,
+         * once each for a^0 and intermediate result.
+         */
+        if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
+        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(r, top, powerbuf, 0, numPowers)) goto err;
 
-        /* lay down tmp and am right after powers table */
-        tmp.d     = (BN_ULONG *)(powerbuf + sizeof(m->d[0])*top*numPowers);
-        am.d      = tmp.d + top;
-        tmp.top   = am.top  = 0;
-        tmp.dmax  = am.dmax = top;
-        tmp.neg   = am.neg  = 0;
-        tmp.flags = am.flags = BN_FLG_STATIC_DATA;
-
-        /* prepare a^0 in Montgomery domain */
-#if 1
-        if (!BN_to_montgomery(&tmp,BN_value_one(),mont,ctx))    goto err;
-#else
-        tmp.d[0] = (0-m->d[0])&BN_MASK2;        /* 2^(top*BN_BITS2) - m */
-        for (i=1;i<top;i++)
-                tmp.d[i] = (~m->d[i])&BN_MASK2;
-        tmp.top = top;
-#endif
+        /* Initialize computeTemp as a^1 with montgomery precalcs */
+        computeTemp = BN_CTX_get(ctx);
+        am = BN_CTX_get(ctx);
+        if (computeTemp==NULL || am==NULL) goto err;
 
-        /* prepare a^1 in Montgomery domain */
         if (a->neg || BN_ucmp(a,m) >= 0)
                 {
-                if (!BN_mod(&am,a,m,ctx))                       goto err;
-                if (!BN_to_montgomery(&am,&am,mont,ctx))        goto err;
-                }
-        else    if (!BN_to_montgomery(&am,a,mont,ctx))          goto err;
-
-#if defined(OPENSSL_BN_ASM_MONT5)
-    /* This optimization uses ideas from http://eprint.iacr.org/2011/239,
-     * specifically optimization of cache-timing attack countermeasures
-     * and pre-computation optimization. */
-
-    /* Dedicated window==4 case improves 512-bit RSA sign by ~15%, but as
-     * 512-bit RSA is hardly relevant, we omit it to spare size... */ 
-    if (window==5)
-        {
-        void bn_mul_mont_gather5(BN_ULONG *rp,const BN_ULONG *ap,
-                        const void *table,const BN_ULONG *np,
-                        const BN_ULONG *n0,int num,int power);
-        void bn_scatter5(const BN_ULONG *inp,size_t num,
-                        void *table,size_t power);
-        void bn_gather5(BN_ULONG *out,size_t num,
-                        void *table,size_t power);
-
-        BN_ULONG *np=mont->N.d, *n0=mont->n0;
-
-        /* BN_to_montgomery can contaminate words above .top
-         * [in BN_DEBUG[_DEBUG] build]... */
-        for (i=am.top; i<top; i++)      am.d[i]=0;
-        for (i=tmp.top; i<top; i++)     tmp.d[i]=0;
-
-        bn_scatter5(tmp.d,top,powerbuf,0);
-        bn_scatter5(am.d,am.top,powerbuf,1);
-        bn_mul_mont(tmp.d,am.d,am.d,np,n0,top);
-        bn_scatter5(tmp.d,top,powerbuf,2);
-
-#if 0
-        for (i=3; i<32; i++)
-                {
-                /* Calculate a^i = a^(i-1) * a */
-                bn_mul_mont_gather5(tmp.d,am.d,powerbuf,np,n0,top,i-1);
-                bn_scatter5(tmp.d,top,powerbuf,i);
-                }
-#else
-        /* same as above, but uses squaring for 1/2 of operations */
-        for (i=4; i<32; i*=2)
-                {
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_scatter5(tmp.d,top,powerbuf,i);
-                }
-        for (i=3; i<8; i+=2)
-                {
-                int j;
-                bn_mul_mont_gather5(tmp.d,am.d,powerbuf,np,n0,top,i-1);
-                bn_scatter5(tmp.d,top,powerbuf,i);
-                for (j=2*i; j<32; j*=2)
-                        {
-                        bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                        bn_scatter5(tmp.d,top,powerbuf,j);
-                        }
-                }
-        for (; i<16; i+=2)
-                {
-                bn_mul_mont_gather5(tmp.d,am.d,powerbuf,np,n0,top,i-1);
-                bn_scatter5(tmp.d,top,powerbuf,i);
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_scatter5(tmp.d,top,powerbuf,2*i);
-                }
-        for (; i<32; i+=2)
-                {
-                bn_mul_mont_gather5(tmp.d,am.d,powerbuf,np,n0,top,i-1);
-                bn_scatter5(tmp.d,top,powerbuf,i);
-                }
-#endif
-        bits--;
-        for (wvalue=0, i=bits%5; i>=0; i--,bits--)
-                wvalue = (wvalue<<1)+BN_is_bit_set(p,bits);
-        bn_gather5(tmp.d,top,powerbuf,wvalue);
-
-        /* Scan the exponent one window at a time starting from the most
-         * significant bits.
-         */
-        while (bits >= 0)
-                {
-                for (wvalue=0, i=0; i<5; i++,bits--)
-                        wvalue = (wvalue<<1)+BN_is_bit_set(p,bits);
-
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_mul_mont(tmp.d,tmp.d,tmp.d,np,n0,top);
-                bn_mul_mont_gather5(tmp.d,tmp.d,powerbuf,np,n0,top,wvalue);
+                if (!BN_mod(am,a,m,ctx))
+                        goto err;
+                aa= am;
                 }
-
-        tmp.top=top;
-        bn_correct_top(&tmp);
-        }
-    else
-#endif
-        {
-        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0, numPowers)) goto err;
-        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am,  top, powerbuf, 1, numPowers)) goto err;
+        else
+                aa=a;
+        if (!BN_to_montgomery(am,aa,mont,ctx)) goto err;
+        if (!BN_copy(computeTemp, am)) goto err;
+        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(am, top, powerbuf, 1, numPowers)) goto err;
 
         /* If the window size is greater than 1, then calculate
          * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1)
@@ -777,54 +662,62 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
          */
         if (window > 1)
                 {
-                if (!BN_mod_mul_montgomery(&tmp,&am,&am,mont,ctx))      goto err;
-                if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 2, numPowers)) goto err;
-                for (i=3; i<numPowers; i++)
+                for (i=2; i<numPowers; i++)
                         {
                         /* Calculate a^i = a^(i-1) * a */
-                        if (!BN_mod_mul_montgomery(&tmp,&am,&tmp,mont,ctx))
+                        if (!BN_mod_mul_montgomery(computeTemp,am,computeTemp,mont,ctx))
                                 goto err;
-                        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, i, numPowers)) goto err;
+                        if (!MOD_EXP_CTIME_COPY_TO_PREBUF(computeTemp, top, powerbuf, i, numPowers)) goto err;
                         }
                 }
 
-        bits--;
-        for (wvalue=0, i=bits%window; i>=0; i--,bits--)
-                wvalue = (wvalue<<1)+BN_is_bit_set(p,bits);
-        if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp,top,powerbuf,wvalue,numPowers)) goto err;
- 
-        /* Scan the exponent one window at a time starting from the most
-         * significant bits.
-         */
-        while (bits >= 0)
+        /* Adjust the number of bits up to a multiple of the window size.
+         * If the exponent length is not a multiple of the window size, then
+         * this pads the most significant bits with zeros to normalize the
+         * scanning loop to there's no special cases.
+         *
+         * * NOTE: Making the window size a power of two less than the native
+         * * word size ensures that the padded bits won't go past the last
+         * * word in the internal BIGNUM structure. Going past the end will
+         * * still produce the correct result, but causes a different branch
+         * * to be taken in the BN_is_bit_set function.
+         */
+        bits = ((bits+window-1)/window)*window;
+        idx=bits-1;     /* The top bit of the window */
+
+        /* Scan the exponent one window at a time starting from the most
+         * significant bits.
+         */
+        while (idx >= 0)
                 {
                 wvalue=0; /* The 'value' of the window */
                 
                 /* Scan the window, squaring the result as we go */
-                for (i=0; i<window; i++,bits--)
+                for (i=0; i<window; i++,idx--)
                         {
-                        if (!BN_mod_mul_montgomery(&tmp,&tmp,&tmp,mont,ctx))    goto err;
-                        wvalue = (wvalue<<1)+BN_is_bit_set(p,bits);
+                        if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))     goto err;
+                        wvalue = (wvalue<<1)+BN_is_bit_set(p,idx);
                         }
                 
                 /* Fetch the appropriate pre-computed value from the pre-buf */
-                if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf, wvalue, numPowers)) goto err;
+                if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(computeTemp, top, powerbuf, wvalue, numPowers)) goto err;
 
                 /* Multiply the result into the intermediate result */
-                if (!BN_mod_mul_montgomery(&tmp,&tmp,&am,mont,ctx)) goto err;
+                if (!BN_mod_mul_montgomery(r,r,computeTemp,mont,ctx)) goto err;
                 }
-        }
 
         /* Convert the final result from montgomery to standard format */
-        if (!BN_from_montgomery(rr,&tmp,mont,ctx)) goto err;
+        if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
         ret=1;
 err:
         if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
         if (powerbuf!=NULL)
                 {
                 OPENSSL_cleanse(powerbuf,powerbufLen);
-                if (powerbufFree) OPENSSL_free(powerbufFree);
+                OPENSSL_free(powerbufFree);
                 }
+        if (am!=NULL) BN_clear(am);
+        if (computeTemp!=NULL) BN_clear(computeTemp);
         BN_CTX_end(ctx);
         return(ret);
         }
@@ -1095,3 +988,4 @@ err:
         bn_check_top(r);
         return(ret);
         }
+