[OE-core] [PATCH][pyro 2/2] libgcrypt: fix CVE-2017-7526
Ross Burton
ross.burton at intel.com
Tue Jul 18 22:07:09 UTC 2017
Fixes CVE-2017-7526, 'flush+reload side-channel attack on RSA secret keys dubbed
"Sliding right into disaster"'.
Signed-off-by: Ross Burton <ross.burton at intel.com>
---
.../libgcrypt/files/CVE-2017-7526.patch | 455 +++++++++++++++++++++
meta/recipes-support/libgcrypt/libgcrypt.inc | 1 +
2 files changed, 456 insertions(+)
create mode 100644 meta/recipes-support/libgcrypt/files/CVE-2017-7526.patch
diff --git a/meta/recipes-support/libgcrypt/files/CVE-2017-7526.patch b/meta/recipes-support/libgcrypt/files/CVE-2017-7526.patch
new file mode 100644
index 00000000000..384fa964ae5
--- /dev/null
+++ b/meta/recipes-support/libgcrypt/files/CVE-2017-7526.patch
@@ -0,0 +1,455 @@
+Flush+reload side-channel attack on RSA secret keys dubbed "Sliding right
+into disaster".
+
+CVE: CVE-2017-7526
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+
+From 12ee400c39e0ebb5fb819c3926d459c278fc99fd Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe at fsij.org>
+Date: Tue, 4 Apr 2017 17:38:05 +0900
+Subject: [PATCH 1/5] mpi: Simplify mpi_powm.
+
+* mpi/mpi-pow.c (_gcry_mpi_powm): Simplify the loop.
+
+--
+
+This fix is not a solution for the problem reported (yet). The
+problem is that the current algorithm of _gcry_mpi_powm depends on
+exponent and some information leaks is possible.
+
+Reported-by: Andreas Zankl <andreas.zankl at aisec.fraunhofer.de>
+Signed-off-by: NIIBE Yutaka <gniibe at fsij.org>
+
+(backport from master commit:
+719468e53133d3bdf12156c5bfdea2bf15f9f6f1)
+
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+---
+ mpi/mpi-pow.c | 105 +++++++++++++++++-----------------------------------------
+ 1 file changed, 30 insertions(+), 75 deletions(-)
+
+diff --git a/mpi/mpi-pow.c b/mpi/mpi-pow.c
+index a780ebd1..7b3dc318 100644
+--- a/mpi/mpi-pow.c
++++ b/mpi/mpi-pow.c
+@@ -609,12 +609,8 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ if (e == 0)
+ {
+ j += c;
+- i--;
+- if ( i < 0 )
+- {
+- c = 0;
+- break;
+- }
++ if ( --i < 0 )
++ break;
+
+ e = ep[i];
+ c = BITS_PER_MPI_LIMB;
+@@ -629,38 +625,33 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ c -= c0;
+ j += c0;
+
++ e0 = (e >> (BITS_PER_MPI_LIMB - W));
+ if (c >= W)
+- {
+- e0 = (e >> (BITS_PER_MPI_LIMB - W));
+- e = (e << W);
+- c -= W;
+- }
++ c0 = 0;
+ else
+ {
+- i--;
+- if ( i < 0 )
++ if ( --i < 0 )
+ {
+- e = (e >> (BITS_PER_MPI_LIMB - c));
+- break;
++ e0 = (e >> (BITS_PER_MPI_LIMB - c));
++ j += c - W;
++ goto last_step;
++ }
++ else
++ {
++ c0 = c;
++ e = ep[i];
++ c = BITS_PER_MPI_LIMB;
++ e0 |= (e >> (BITS_PER_MPI_LIMB - (W - c0)));
+ }
+-
+- c0 = c;
+- e0 = (e >> (BITS_PER_MPI_LIMB - W))
+- | (ep[i] >> (BITS_PER_MPI_LIMB - W + c0));
+- e = (ep[i] << (W - c0));
+- c = BITS_PER_MPI_LIMB - W + c0;
+ }
+
++ e = e << (W - c0);
++ c -= (W - c0);
++
++ last_step:
+ count_trailing_zeros (c0, e0);
+ e0 = (e0 >> c0) >> 1;
+
+- for (j += W - c0; j; j--)
+- {
+- mul_mod (xp, &xsize, rp, rsize, rp, rsize, mp, msize, &karactx);
+- tp = rp; rp = xp; xp = tp;
+- rsize = xsize;
+- }
+-
+ /*
+ * base_u <= precomp[e0]
+ * base_u_size <= precomp_size[e0]
+@@ -677,25 +668,23 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ u.d = precomp[k];
+
+ mpi_set_cond (&w, &u, k == e0);
+- base_u_size |= (precomp_size[k] & ((mpi_size_t)0 - (k == e0)) );
++ base_u_size |= ( precomp_size[k] & ((mpi_size_t)0 - (k == e0)) );
+ }
+
+- mul_mod (xp, &xsize, rp, rsize, base_u, base_u_size,
+- mp, msize, &karactx);
+- tp = rp; rp = xp; xp = tp;
+- rsize = xsize;
++ for (j += W - c0; j >= 0; j--)
++ {
++ mul_mod (xp, &xsize, rp, rsize,
++ j == 0 ? base_u : rp, j == 0 ? base_u_size : rsize,
++ mp, msize, &karactx);
++ tp = rp; rp = xp; xp = tp;
++ rsize = xsize;
++ }
+
+ j = c0;
++ if ( i < 0 )
++ break;
+ }
+
+- if (c != 0)
+- {
+- j += c;
+- count_trailing_zeros (c, e);
+- e = (e >> c);
+- j -= c;
+- }
+-
+ while (j--)
+ {
+ mul_mod (xp, &xsize, rp, rsize, rp, rsize, mp, msize, &karactx);
+@@ -703,40 +692,6 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ rsize = xsize;
+ }
+
+- if (e != 0)
+- {
+- /*
+- * base_u <= precomp[(e>>1)]
+- * base_u_size <= precomp_size[(e>>1)]
+- */
+- base_u_size = 0;
+- for (k = 0; k < (1<< (W - 1)); k++)
+- {
+- struct gcry_mpi w, u;
+- w.alloced = w.nlimbs = precomp_size[k];
+- u.alloced = u.nlimbs = precomp_size[k];
+- w.sign = u.sign = 0;
+- w.flags = u.flags = 0;
+- w.d = base_u;
+- u.d = precomp[k];
+-
+- mpi_set_cond (&w, &u, k == (e>>1));
+- base_u_size |= (precomp_size[k] & ((mpi_size_t)0 - (k == (e>>1))) );
+- }
+-
+- mul_mod (xp, &xsize, rp, rsize, base_u, base_u_size,
+- mp, msize, &karactx);
+- tp = rp; rp = xp; xp = tp;
+- rsize = xsize;
+-
+- for (; c; c--)
+- {
+- mul_mod (xp, &xsize, rp, rsize, rp, rsize, mp, msize, &karactx);
+- tp = rp; rp = xp; xp = tp;
+- rsize = xsize;
+- }
+- }
+-
+ /* We shifted MOD, the modulo reduction argument, left
+ MOD_SHIFT_CNT steps. Adjust the result by reducing it with the
+ original MOD.
+--
+2.11.0
+
+
+From a4b275c4d5378837e820fdc84f4ada876f9c8ccd Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe at fsij.org>
+Date: Sat, 24 Jun 2017 20:46:20 +0900
+Subject: [PATCH 2/5] Same computation for square and multiply.
+
+* mpi/mpi-pow.c (_gcry_mpi_powm): Compare msize for max_u_size. Move
+the assignment to base_u into the loop. Copy content refered by RP to
+BASE_U except the last of the loop.
+
+--
+
+Signed-off-by: NIIBE Yutaka <gniibe at fsij.org>
+(backport from master commit:
+78130828e9a140a9de4dafadbc844dbb64cb709a)
+
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+---
+ mpi/mpi-pow.c | 50 +++++++++++++++++++++++++++++---------------------
+ 1 file changed, 29 insertions(+), 21 deletions(-)
+
+diff --git a/mpi/mpi-pow.c b/mpi/mpi-pow.c
+index 7b3dc318..3cba6903 100644
+--- a/mpi/mpi-pow.c
++++ b/mpi/mpi-pow.c
+@@ -573,6 +573,8 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ MPN_COPY (precomp[i], rp, rsize);
+ }
+
++ if (msize > max_u_size)
++ max_u_size = msize;
+ base_u = mpi_alloc_limb_space (max_u_size, esec);
+ MPN_ZERO (base_u, max_u_size);
+
+@@ -619,6 +621,10 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ {
+ int c0;
+ mpi_limb_t e0;
++ struct gcry_mpi w, u;
++ w.sign = u.sign = 0;
++ w.flags = u.flags = 0;
++ w.d = base_u;
+
+ count_leading_zeros (c0, e);
+ e = (e << c0);
+@@ -652,29 +658,31 @@ _gcry_mpi_powm (gcry_mpi_t res,
+ count_trailing_zeros (c0, e0);
+ e0 = (e0 >> c0) >> 1;
+
+- /*
+- * base_u <= precomp[e0]
+- * base_u_size <= precomp_size[e0]
+- */
+- base_u_size = 0;
+- for (k = 0; k < (1<< (W - 1)); k++)
+- {
+- struct gcry_mpi w, u;
+- w.alloced = w.nlimbs = precomp_size[k];
+- u.alloced = u.nlimbs = precomp_size[k];
+- w.sign = u.sign = 0;
+- w.flags = u.flags = 0;
+- w.d = base_u;
+- u.d = precomp[k];
+-
+- mpi_set_cond (&w, &u, k == e0);
+- base_u_size |= ( precomp_size[k] & ((mpi_size_t)0 - (k == e0)) );
+- }
+-
+ for (j += W - c0; j >= 0; j--)
+ {
+- mul_mod (xp, &xsize, rp, rsize,
+- j == 0 ? base_u : rp, j == 0 ? base_u_size : rsize,
++
++ /*
++ * base_u <= precomp[e0]
++ * base_u_size <= precomp_size[e0]
++ */
++ base_u_size = 0;
++ for (k = 0; k < (1<< (W - 1)); k++)
++ {
++ w.alloced = w.nlimbs = precomp_size[k];
++ u.alloced = u.nlimbs = precomp_size[k];
++ u.d = precomp[k];
++
++ mpi_set_cond (&w, &u, k == e0);
++ base_u_size |= ( precomp_size[k] & (0UL - (k == e0)) );
++ }
++
++ w.alloced = w.nlimbs = rsize;
++ u.alloced = u.nlimbs = rsize;
++ u.d = rp;
++ mpi_set_cond (&w, &u, j != 0);
++ base_u_size ^= ((base_u_size ^ rsize) & (0UL - (j != 0)));
++
++ mul_mod (xp, &xsize, rp, rsize, base_u, base_u_size,
+ mp, msize, &karactx);
+ tp = rp; rp = xp; xp = tp;
+ rsize = xsize;
+--
+2.11.0
+
+
+From 129c1960e55603ec3f6fd1cd9cd51b22e9a9a7ef Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe at fsij.org>
+Date: Thu, 29 Jun 2017 11:48:44 +0900
+Subject: [PATCH 3/5] rsa: Add exponent blinding.
+
+* cipher/rsa.c (secret): Blind secret D with randomized nonce R for
+mpi_powm computation.
+
+--
+
+Co-authored-by: Werner Koch <wk at gnupg.org>
+Signed-off-by: NIIBE Yutaka <gniibe at fsij.org>
+
+The paper describing attack: https://eprint.iacr.org/2017/627
+
+Sliding right into disaster: Left-to-right sliding windows leak
+by Daniel J. Bernstein and Joachim Breitner and Daniel Genkin and
+Leon Groot Bruinderink and Nadia Heninger and Tanja Lange and
+Christine van Vredendaal and Yuval Yarom
+
+ It is well known that constant-time implementations of modular
+ exponentiation cannot use sliding windows. However, software
+ libraries such as Libgcrypt, used by GnuPG, continue to use sliding
+ windows. It is widely believed that, even if the complete pattern of
+ squarings and multiplications is observed through a side-channel
+ attack, the number of exponent bits leaked is not sufficient to
+ carry out a full key-recovery attack against RSA. Specifically,
+ 4-bit sliding windows leak only 40% of the bits, and 5-bit sliding
+ windows leak only 33% of the bits.
+
+ In this paper we demonstrate a complete break of RSA-1024 as
+ implemented in Libgcrypt. Our attack makes essential use of the fact
+ that Libgcrypt uses the left-to-right method for computing the
+ sliding-window expansion. We show for the first time that the
+ direction of the encoding matters: the pattern of squarings and
+ multiplications in left-to-right sliding windows leaks significantly
+ more information about exponent bits than for right-to-left. We show
+ how to incorporate this additional information into the
+ Heninger-Shacham algorithm for partial key reconstruction, and use
+ it to obtain very efficient full key recovery for RSA-1024. We also
+ provide strong evidence that the same attack works for RSA-2048 with
+ only moderately more computation.
+
+Exponent blinding is a kind of workaround to add noise. Signal (leak)
+is still there for non-constant-time implementation.
+
+(backported from master commit:
+8725c99ffa41778f382ca97233183bcd687bb0ce)
+
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+---
+ cipher/rsa.c | 32 +++++++++++++++++++++++++-------
+ 1 file changed, 25 insertions(+), 7 deletions(-)
+
+diff --git a/cipher/rsa.c b/cipher/rsa.c
+index b6c73741..25e29b5c 100644
+--- a/cipher/rsa.c
++++ b/cipher/rsa.c
+@@ -1021,15 +1021,33 @@ secret (gcry_mpi_t output, gcry_mpi_t input, RSA_secret_key *skey )
+ gcry_mpi_t m1 = mpi_alloc_secure( mpi_get_nlimbs(skey->n)+1 );
+ gcry_mpi_t m2 = mpi_alloc_secure( mpi_get_nlimbs(skey->n)+1 );
+ gcry_mpi_t h = mpi_alloc_secure( mpi_get_nlimbs(skey->n)+1 );
+-
+- /* m1 = c ^ (d mod (p-1)) mod p */
++ gcry_mpi_t D_blind = mpi_alloc_secure ( mpi_get_nlimbs(skey->n) + 1 );
++ gcry_mpi_t r;
++ unsigned int r_nbits;
++
++ r_nbits = mpi_get_nbits (skey->p) / 4;
++ if (r_nbits < 96)
++ r_nbits = 96;
++ r = mpi_alloc_secure ((r_nbits + BITS_PER_MPI_LIMB-1)/BITS_PER_MPI_LIMB);
++
++ /* d_blind = (d mod (p-1)) + (p-1) * r */
++ /* m1 = c ^ d_blind mod p */
++ _gcry_mpi_randomize (r, r_nbits, GCRY_WEAK_RANDOM);
++ mpi_set_highbit (r, r_nbits - 1);
+ mpi_sub_ui( h, skey->p, 1 );
+- mpi_fdiv_r( h, skey->d, h );
+- mpi_powm( m1, input, h, skey->p );
+- /* m2 = c ^ (d mod (q-1)) mod q */
++ mpi_mul ( D_blind, h, r );
++ mpi_fdiv_r ( h, skey->d, h );
++ mpi_add ( D_blind, D_blind, h );
++ mpi_powm( m1, input, D_blind, skey->p );
++ /* d_blind = (d mod (q-1)) + (q-1) * r */
++ /* m2 = c ^ d_blind mod q */
++ _gcry_mpi_randomize (r, r_nbits, GCRY_WEAK_RANDOM);
++ mpi_set_highbit (r, r_nbits - 1);
+ mpi_sub_ui( h, skey->q, 1 );
+- mpi_fdiv_r( h, skey->d, h );
+- mpi_powm( m2, input, h, skey->q );
++ mpi_mul ( D_blind, h, r );
++ mpi_fdiv_r ( h, skey->d, h );
++ mpi_add ( D_blind, D_blind, h );
++ mpi_powm( m2, input, D_blind, skey->q );
+ /* h = u * ( m2 - m1 ) mod q */
+ mpi_sub( h, m2, m1 );
+ if ( mpi_has_sign ( h ) )
+--
+2.11.0
+
+
+From 8e1a6289b7d11a8bf6c94affa06c9794e7216e26 Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe at fsij.org>
+Date: Thu, 29 Jun 2017 12:36:27 +0900
+Subject: [PATCH 4/5] rsa: Fix exponent blinding.
+
+* cipher/rsa.c (secret): Free D_BLIND.
+
+--
+
+Fixes-commit: a9f612def801c8145d551d995475e5d51a4c988c
+Signed-off-by: NIIBE Yutaka <gniibe at fsij.org>
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+---
+ cipher/rsa.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/cipher/rsa.c b/cipher/rsa.c
+index 25e29b5c..33f92ebd 100644
+--- a/cipher/rsa.c
++++ b/cipher/rsa.c
+@@ -1057,6 +1057,7 @@ secret (gcry_mpi_t output, gcry_mpi_t input, RSA_secret_key *skey )
+ mpi_mul ( h, h, skey->p );
+ mpi_add ( output, m1, h );
+
++ mpi_free ( D_blind );
+ mpi_free ( h );
+ mpi_free ( m1 );
+ mpi_free ( m2 );
+--
+2.11.0
+
+
+From 4e5497752172edc444029af645f28cb88ce93906 Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe at fsij.org>
+Date: Thu, 29 Jun 2017 12:40:19 +0900
+Subject: [PATCH 5/5] rsa: More fix.
+
+* cipher/rsa.c (secret): Free R.
+
+--
+
+Fixes-commit: a9f612def801c8145d551d995475e5d51a4c988c
+Signed-off-by: NIIBE Yutaka <gniibe at fsij.org>
+Signed-off-by: Ross Burton <ross.burton at intel.com>
+---
+ cipher/rsa.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/cipher/rsa.c b/cipher/rsa.c
+index 33f92ebd..8d8d157b 100644
+--- a/cipher/rsa.c
++++ b/cipher/rsa.c
+@@ -1057,6 +1057,7 @@ secret (gcry_mpi_t output, gcry_mpi_t input, RSA_secret_key *skey )
+ mpi_mul ( h, h, skey->p );
+ mpi_add ( output, m1, h );
+
++ mpi_free ( r );
+ mpi_free ( D_blind );
+ mpi_free ( h );
+ mpi_free ( m1 );
+--
+2.11.0
+
diff --git a/meta/recipes-support/libgcrypt/libgcrypt.inc b/meta/recipes-support/libgcrypt/libgcrypt.inc
index e95c059c875..3403579a70f 100644
--- a/meta/recipes-support/libgcrypt/libgcrypt.inc
+++ b/meta/recipes-support/libgcrypt/libgcrypt.inc
@@ -21,6 +21,7 @@ SRC_URI = "${GNUPG_MIRROR}/libgcrypt/libgcrypt-${PV}.tar.gz \
file://fix-ICE-failure-on-mips-with-option-O-and-g.patch \
file://fix-undefined-reference-to-pthread.patch \
file://0001-ecc-Store-EdDSA-session-key-in-secure-memory.patch \
+ file://CVE-2017-7526.patch \
"
BINCONFIG = "${bindir}/libgcrypt-config"
--
2.11.0
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