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openssl-CVE-2022-4304.patch
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File openssl-CVE-2022-4304.patch of Package openssl-1_1
From aefe424d7695ed13b240673298d340bc552365fe Mon Sep 17 00:00:00 2001 From: Bernd Edlinger <bernd.edlinger@hotmail.de> Date: Mon, 13 Feb 2023 17:46:41 +0100 Subject: [PATCH] Alternative fix for CVE-2022-4304 This is about a timing leak in the topmost limb of the internal result of RSA_private_decrypt, before the padding check. There are in fact at least three bugs together that caused the timing leak: First and probably most important is the fact that the blinding did not use the constant time code path at all when the RSA object was used for a private decrypt, due to the fact that the Montgomery context rsa->_method_mod_n was not set up early enough in rsa_ossl_private_decrypt, when BN_BLINDING_create_param needed it, and that was persisted as blinding->m_ctx, although the RSA object creates the Montgomery context just a bit later. Then the infamous bn_correct_top was used on the secret value right after the blinding was removed. And finally the function BN_bn2binpad did not use the constant-time code path since the BN_FLG_CONSTTIME was not set on the secret value. In order to address the first problem, this patch makes sure that the rsa->_method_mod_n is initialized right before the blinding context. And to fix the second problem, we add a new utility function bn_correct_top_consttime, a const-time variant of bn_correct_top. Together with the fact, that BN_bn2binpad is already constant time if the flag BN_FLG_CONSTTIME is set, this should eliminate the timing oracle completely. In addition the no-asm variant may also have branches that depend on secret values, because the last invocation of bn_sub_words in bn_from_montgomery_word had branches when the function is compiled by certain gcc compiler versions, due to the clumsy coding style. So additionally this patch stream-lined the no-asm C-code in order to avoid branches where possible and improve the resulting code quality. --- CHANGES | 10 ++++ crypto/bn/bn_asm.c | 106 +++++++++++++++++++++++++++----------------------- crypto/bn/bn_blind.c | 3 - crypto/bn/bn_lib.c | 22 ++++++++++ crypto/bn/bn_local.h | 26 ++++++------ crypto/rsa/rsa_ossl.c | 13 ++---- 6 files changed, 111 insertions(+), 69 deletions(-) --- a/CHANGES +++ b/CHANGES @@ -9,6 +9,16 @@ Changes between 1.1.1k and 1.1.1l [24 Aug 2021] + *) Reworked the Fix for the Timing Oracle in RSA Decryption (CVE-2022-4304). + The previous fix for this timing side channel turned out to cause + a severe 2-3x performance regression in the typical use case + compared to 1.1.1s. The new fix uses existing constant time + code paths, and restores the previous performance level while + fully eliminating all existing timing side channels. + The fix was developed by Bernd Edlinger with testing support + by Hubert Kario. + [Bernd Edlinger] + *) Fixed an SM2 Decryption Buffer Overflow. In order to decrypt SM2 encrypted data an application is expected to call the --- a/crypto/bn/bn_asm.c +++ b/crypto/bn/bn_asm.c @@ -381,25 +381,33 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const #ifndef OPENSSL_SMALL_FOOTPRINT while (n & ~3) { t1 = a[0]; - t2 = b[0]; - r[0] = (t1 - t2 - c) & BN_MASK2; - if (t1 != t2) - c = (t1 < t2); + t2 = (t1 - c) & BN_MASK2; + c = (t2 > t1); + t1 = b[0]; + t1 = (t2 - t1) & BN_MASK2; + r[0] = t1; + c += (t1 > t2); t1 = a[1]; - t2 = b[1]; - r[1] = (t1 - t2 - c) & BN_MASK2; - if (t1 != t2) - c = (t1 < t2); + t2 = (t1 - c) & BN_MASK2; + c = (t2 > t1); + t1 = b[1]; + t1 = (t2 - t1) & BN_MASK2; + r[1] = t1; + c += (t1 > t2); t1 = a[2]; - t2 = b[2]; - r[2] = (t1 - t2 - c) & BN_MASK2; - if (t1 != t2) - c = (t1 < t2); + t2 = (t1 - c) & BN_MASK2; + c = (t2 > t1); + t1 = b[2]; + t1 = (t2 - t1) & BN_MASK2; + r[2] = t1; + c += (t1 > t2); t1 = a[3]; - t2 = b[3]; - r[3] = (t1 - t2 - c) & BN_MASK2; - if (t1 != t2) - c = (t1 < t2); + t2 = (t1 - c) & BN_MASK2; + c = (t2 > t1); + t1 = b[3]; + t1 = (t2 - t1) & BN_MASK2; + r[3] = t1; + c += (t1 > t2); a += 4; b += 4; r += 4; @@ -408,10 +416,12 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const #endif while (n) { t1 = a[0]; - t2 = b[0]; - r[0] = (t1 - t2 - c) & BN_MASK2; - if (t1 != t2) - c = (t1 < t2); + t2 = (t1 - c) & BN_MASK2; + c = (t2 > t1); + t1 = b[0]; + t1 = (t2 - t1) & BN_MASK2; + r[0] = t1; + c += (t1 > t2); a++; b++; r++; @@ -446,7 +456,7 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const t += c0; /* no carry */ \ c0 = (BN_ULONG)Lw(t); \ hi = (BN_ULONG)Hw(t); \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define mul_add_c2(a,b,c0,c1,c2) do { \ @@ -455,11 +465,11 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULLONG tt = t+c0; /* no carry */ \ c0 = (BN_ULONG)Lw(tt); \ hi = (BN_ULONG)Hw(tt); \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ t += c0; /* no carry */ \ c0 = (BN_ULONG)Lw(t); \ hi = (BN_ULONG)Hw(t); \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define sqr_add_c(a,i,c0,c1,c2) do { \ @@ -468,7 +478,7 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const t += c0; /* no carry */ \ c0 = (BN_ULONG)Lw(t); \ hi = (BN_ULONG)Hw(t); \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define sqr_add_c2(a,i,j,c0,c1,c2) \ @@ -483,26 +493,26 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULONG ta = (a), tb = (b); \ BN_ULONG lo, hi; \ BN_UMULT_LOHI(lo,hi,ta,tb); \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define mul_add_c2(a,b,c0,c1,c2) do { \ BN_ULONG ta = (a), tb = (b); \ BN_ULONG lo, hi, tt; \ BN_UMULT_LOHI(lo,hi,ta,tb); \ - c0 += lo; tt = hi+((c0<lo)?1:0); \ - c1 += tt; c2 += (c1<tt)?1:0; \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; tt = hi + (c0<lo); \ + c1 += tt; c2 += (c1<tt); \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define sqr_add_c(a,i,c0,c1,c2) do { \ BN_ULONG ta = (a)[i]; \ BN_ULONG lo, hi; \ BN_UMULT_LOHI(lo,hi,ta,ta); \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define sqr_add_c2(a,i,j,c0,c1,c2) \ @@ -517,26 +527,26 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULONG ta = (a), tb = (b); \ BN_ULONG lo = ta * tb; \ BN_ULONG hi = BN_UMULT_HIGH(ta,tb); \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define mul_add_c2(a,b,c0,c1,c2) do { \ BN_ULONG ta = (a), tb = (b), tt; \ BN_ULONG lo = ta * tb; \ BN_ULONG hi = BN_UMULT_HIGH(ta,tb); \ - c0 += lo; tt = hi + ((c0<lo)?1:0); \ - c1 += tt; c2 += (c1<tt)?1:0; \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; tt = hi + (c0<lo); \ + c1 += tt; c2 += (c1<tt); \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define sqr_add_c(a,i,c0,c1,c2) do { \ BN_ULONG ta = (a)[i]; \ BN_ULONG lo = ta * ta; \ BN_ULONG hi = BN_UMULT_HIGH(ta,ta); \ - c0 += lo; hi += (c0<lo)?1:0; \ - c1 += hi; c2 += (c1<hi)?1:0; \ + c0 += lo; hi += (c0<lo); \ + c1 += hi; c2 += (c1<hi); \ } while(0) # define sqr_add_c2(a,i,j,c0,c1,c2) \ @@ -551,8 +561,8 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULONG lo = LBITS(a), hi = HBITS(a); \ BN_ULONG bl = LBITS(b), bh = HBITS(b); \ mul64(lo,hi,bl,bh); \ - c0 = (c0+lo)&BN_MASK2; if (c0<lo) hi++; \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c0 = (c0+lo)&BN_MASK2; hi += (c0<lo); \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define mul_add_c2(a,b,c0,c1,c2) do { \ @@ -561,17 +571,17 @@ BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULONG bl = LBITS(b), bh = HBITS(b); \ mul64(lo,hi,bl,bh); \ tt = hi; \ - c0 = (c0+lo)&BN_MASK2; if (c0<lo) tt++; \ - c1 = (c1+tt)&BN_MASK2; if (c1<tt) c2++; \ - c0 = (c0+lo)&BN_MASK2; if (c0<lo) hi++; \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c0 = (c0+lo)&BN_MASK2; tt += (c0<lo); \ + c1 = (c1+tt)&BN_MASK2; c2 += (c1<tt); \ + c0 = (c0+lo)&BN_MASK2; hi += (c0<lo); \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define sqr_add_c(a,i,c0,c1,c2) do { \ BN_ULONG lo, hi; \ sqr64(lo,hi,(a)[i]); \ - c0 = (c0+lo)&BN_MASK2; if (c0<lo) hi++; \ - c1 = (c1+hi)&BN_MASK2; if (c1<hi) c2++; \ + c0 = (c0+lo)&BN_MASK2; hi += (c0<lo); \ + c1 = (c1+hi)&BN_MASK2; c2 += (c1<hi); \ } while(0) # define sqr_add_c2(a,i,j,c0,c1,c2) \ --- a/crypto/bn/bn_blind.c +++ b/crypto/bn/bn_blind.c @@ -191,7 +191,8 @@ int BN_BLINDING_invert_ex(BIGNUM *n, con n->top = (int)(rtop & ~mask) | (ntop & mask); n->flags |= (BN_FLG_FIXED_TOP & ~mask); } - ret = BN_mod_mul_montgomery(n, n, r, b->m_ctx, ctx); + ret = bn_mul_mont_fixed_top(n, n, r, b->m_ctx, ctx); + bn_correct_top_consttime(n); } else { ret = BN_mod_mul(n, n, r, b->mod, ctx); } --- a/crypto/bn/bn_lib.c +++ b/crypto/bn/bn_lib.c @@ -1001,6 +1001,28 @@ BIGNUM *bn_wexpand(BIGNUM *a, int words) return (words <= a->dmax) ? a : bn_expand2(a, words); } +void bn_correct_top_consttime(BIGNUM *a) +{ + int j, atop; + BN_ULONG limb; + unsigned int mask; + + for (j = 0, atop = 0; j < a->dmax; j++) { + limb = a->d[j]; + limb |= 0 - limb; + limb >>= BN_BITS2 - 1; + limb = 0 - limb; + mask = (unsigned int)limb; + mask &= constant_time_msb(j - a->top); + atop = constant_time_select_int(mask, j + 1, atop); + } + + mask = constant_time_eq_int(atop, 0); + a->top = atop; + a->neg = constant_time_select_int(mask, 0, a->neg); + a->flags &= ~BN_FLG_FIXED_TOP; +} + void bn_correct_top(BIGNUM *a) { BN_ULONG *ftl; --- a/crypto/bn/bn_local.h +++ b/crypto/bn/bn_local.h @@ -496,10 +496,10 @@ unsigned __int64 _umul128(unsigned __int ret = (r); \ BN_UMULT_LOHI(low,high,w,tmp); \ ret += (c); \ - (c) = (ret<(c))?1:0; \ + (c) = (ret<(c)); \ (c) += high; \ ret += low; \ - (c) += (ret<low)?1:0; \ + (c) += (ret<low); \ (r) = ret; \ } @@ -508,7 +508,7 @@ unsigned __int64 _umul128(unsigned __int BN_UMULT_LOHI(low,high,w,ta); \ ret = low + (c); \ (c) = high; \ - (c) += (ret<low)?1:0; \ + (c) += (ret<low); \ (r) = ret; \ } @@ -524,10 +524,10 @@ unsigned __int64 _umul128(unsigned __int high= BN_UMULT_HIGH(w,tmp); \ ret += (c); \ low = (w) * tmp; \ - (c) = (ret<(c))?1:0; \ + (c) = (ret<(c)); \ (c) += high; \ ret += low; \ - (c) += (ret<low)?1:0; \ + (c) += (ret<low); \ (r) = ret; \ } @@ -537,7 +537,7 @@ unsigned __int64 _umul128(unsigned __int high= BN_UMULT_HIGH(w,ta); \ ret = low + (c); \ (c) = high; \ - (c) += (ret<low)?1:0; \ + (c) += (ret<low); \ (r) = ret; \ } @@ -570,10 +570,10 @@ unsigned __int64 _umul128(unsigned __int lt=(bl)*(lt); \ m1=(bl)*(ht); \ ht =(bh)*(ht); \ - m=(m+m1)&BN_MASK2; if (m < m1) ht+=L2HBITS((BN_ULONG)1); \ + m=(m+m1)&BN_MASK2; ht += L2HBITS((BN_ULONG)(m < m1)); \ ht+=HBITS(m); \ m1=L2HBITS(m); \ - lt=(lt+m1)&BN_MASK2; if (lt < m1) ht++; \ + lt=(lt+m1)&BN_MASK2; ht += (lt < m1); \ (l)=lt; \ (h)=ht; \ } @@ -590,7 +590,7 @@ unsigned __int64 _umul128(unsigned __int h*=h; \ h+=(m&BN_MASK2h1)>>(BN_BITS4-1); \ m =(m&BN_MASK2l)<<(BN_BITS4+1); \ - l=(l+m)&BN_MASK2; if (l < m) h++; \ + l=(l+m)&BN_MASK2; h += (l < m); \ (lo)=l; \ (ho)=h; \ } @@ -604,9 +604,9 @@ unsigned __int64 _umul128(unsigned __int mul64(l,h,(bl),(bh)); \ \ /* non-multiply part */ \ - l=(l+(c))&BN_MASK2; if (l < (c)) h++; \ + l=(l+(c))&BN_MASK2; h += (l < (c)); \ (c)=(r); \ - l=(l+(c))&BN_MASK2; if (l < (c)) h++; \ + l=(l+(c))&BN_MASK2; h += (l < (c)); \ (c)=h&BN_MASK2; \ (r)=l; \ } @@ -620,7 +620,7 @@ unsigned __int64 _umul128(unsigned __int mul64(l,h,(bl),(bh)); \ \ /* non-multiply part */ \ - l+=(c); if ((l&BN_MASK2) < (c)) h++; \ + l+=(c); h += ((l&BN_MASK2) < (c)); \ (c)=h&BN_MASK2; \ (r)=l&BN_MASK2; \ } @@ -650,7 +650,7 @@ BN_ULONG bn_sub_part_words(BN_ULONG *r, int cl, int dl); int bn_mul_mont(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp, const BN_ULONG *np, const BN_ULONG *n0, int num); - +void bn_correct_top_consttime(BIGNUM *a); BIGNUM *int_bn_mod_inverse(BIGNUM *in, const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx, int *noinv); --- a/crypto/rsa/rsa_ossl.c +++ b/crypto/rsa/rsa_ossl.c @@ -252,6 +252,7 @@ static int rsa_blinding_invert(BN_BLINDI * will only read the modulus from BN_BLINDING. In both cases it's safe * to access the blinding without a lock. */ + BN_set_flags(f, BN_FLG_CONSTTIME); return BN_BLINDING_invert_ex(f, unblind, b, ctx); } @@ -470,6 +471,11 @@ static int rsa_ossl_private_decrypt(int goto err; } + if (rsa->flags & RSA_FLAG_CACHE_PUBLIC) + if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock, + rsa->n, ctx)) + goto err; + if (!(rsa->flags & RSA_FLAG_NO_BLINDING)) { blinding = rsa_get_blinding(rsa, &local_blinding, ctx); if (blinding == NULL) { @@ -507,13 +513,6 @@ static int rsa_ossl_private_decrypt(int goto err; } BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME); - - if (rsa->flags & RSA_FLAG_CACHE_PUBLIC) - if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock, - rsa->n, ctx)) { - BN_free(d); - goto err; - } if (!rsa->meth->bn_mod_exp(ret, f, d, rsa->n, ctx, rsa->_method_mod_n)) { BN_free(d);
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