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2013-10-07crypto: crypto_memneq - add equality testing of memory regions w/o timing leaksJames Yonan
When comparing MAC hashes, AEAD authentication tags, or other hash values in the context of authentication or integrity checking, it is important not to leak timing information to a potential attacker, i.e. when communication happens over a network. Bytewise memory comparisons (such as memcmp) are usually optimized so that they return a nonzero value as soon as a mismatch is found. E.g, on x86_64/i5 for 512 bytes this can be ~50 cyc for a full mismatch and up to ~850 cyc for a full match (cold). This early-return behavior can leak timing information as a side channel, allowing an attacker to iteratively guess the correct result. This patch adds a new method crypto_memneq ("memory not equal to each other") to the crypto API that compares memory areas of the same length in roughly "constant time" (cache misses could change the timing, but since they don't reveal information about the content of the strings being compared, they are effectively benign). Iow, best and worst case behaviour take the same amount of time to complete (in contrast to memcmp). Note that crypto_memneq (unlike memcmp) can only be used to test for equality or inequality, NOT for lexicographical order. This, however, is not an issue for its use-cases within the crypto API. We tried to locate all of the places in the crypto API where memcmp was being used for authentication or integrity checking, and convert them over to crypto_memneq. crypto_memneq is declared noinline, placed in its own source file, and compiled with optimizations that might increase code size disabled ("Os") because a smart compiler (or LTO) might notice that the return value is always compared against zero/nonzero, and might then reintroduce the same early-return optimization that we are trying to avoid. Using #pragma or __attribute__ optimization annotations of the code for disabling optimization was avoided as it seems to be considered broken or unmaintained for long time in GCC [1]. Therefore, we work around that by specifying the compile flag for memneq.o directly in the Makefile. We found that this seems to be most appropriate. As we use ("Os"), this patch also provides a loop-free "fast-path" for frequently used 16 byte digests. Similarly to kernel library string functions, leave an option for future even further optimized architecture specific assembler implementations. This was a joint work of James Yonan and Daniel Borkmann. Also thanks for feedback from Florian Weimer on this and earlier proposals [2]. [1] http://gcc.gnu.org/ml/gcc/2012-07/msg00211.html [2] https://lkml.org/lkml/2013/2/10/131 Signed-off-by: James Yonan <james@openvpn.net> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Cc: Florian Weimer <fw@deneb.enyo.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2013-02-04crypto: use ERR_CASTJulia Lawall
Replace PTR_ERR followed by ERR_PTR by ERR_CAST, to be more concise. The semantic patch that makes this change is as follows: (http://coccinelle.lip6.fr/) // <smpl> @@ expression err,x; @@ - err = PTR_ERR(x); if (IS_ERR(x)) - return ERR_PTR(err); + return ERR_CAST(x); // </smpl> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2012-03-20crypto: remove the second argument of k[un]map_atomic()Cong Wang
Signed-off-by: Cong Wang <amwang@redhat.com>
2009-01-27crypto: ccm - Fix handling of null assoc dataJarod Wilson
Its a valid use case to have null associated data in a ccm vector, but this case isn't being handled properly right now. The following ccm decryption/verification test vector, using the rfc4309 implementation regularly triggers a panic, as will any other vector with null assoc data: * key: ab2f8a74b71cd2b1ff802e487d82f8b9 * iv: c6fb7d800d13abd8a6b2d8 * Associated Data: [NULL] * Tag Length: 8 * input: d5e8939fc7892e2b The resulting panic looks like so: Unable to handle kernel paging request at ffff810064ddaec0 RIP: [<ffffffff8864c4d7>] :ccm:get_data_to_compute+0x1a6/0x1d6 PGD 8063 PUD 0 Oops: 0002 [1] SMP last sysfs file: /module/libata/version CPU 0 Modules linked in: crypto_tester_kmod(U) seqiv krng ansi_cprng chainiv rng ctr aes_generic aes_x86_64 ccm cryptomgr testmgr_cipher testmgr aead crypto_blkcipher crypto_a lgapi des ipv6 xfrm_nalgo crypto_api autofs4 hidp l2cap bluetooth nfs lockd fscache nfs_acl sunrpc ip_conntrack_netbios_ns ipt_REJECT xt_state ip_conntrack nfnetlink xt_ tcpudp iptable_filter ip_tables x_tables dm_mirror dm_log dm_multipath scsi_dh dm_mod video hwmon backlight sbs i2c_ec button battery asus_acpi acpi_memhotplug ac lp sg snd_intel8x0 snd_ac97_codec ac97_bus snd_seq_dummy snd_seq_oss joydev snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss ide_cd snd_pcm floppy parport_p c shpchp e752x_edac snd_timer e1000 i2c_i801 edac_mc snd soundcore snd_page_alloc i2c_core cdrom parport serio_raw pcspkr ata_piix libata sd_mod scsi_mod ext3 jbd uhci_h cd ohci_hcd ehci_hcd Pid: 12844, comm: crypto-tester Tainted: G 2.6.18-128.el5.fips1 #1 RIP: 0010:[<ffffffff8864c4d7>] [<ffffffff8864c4d7>] :ccm:get_data_to_compute+0x1a6/0x1d6 RSP: 0018:ffff8100134434e8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8100104898b0 RCX: ffffffffab6aea10 RDX: 0000000000000010 RSI: ffff8100104898c0 RDI: ffff810064ddaec0 RBP: 0000000000000000 R08: ffff8100104898b0 R09: 0000000000000000 R10: ffff8100103bac84 R11: ffff8100104898b0 R12: ffff810010489858 R13: ffff8100104898b0 R14: ffff8100103bac00 R15: 0000000000000000 FS: 00002ab881adfd30(0000) GS:ffffffff803ac000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: ffff810064ddaec0 CR3: 0000000012a88000 CR4: 00000000000006e0 Process crypto-tester (pid: 12844, threadinfo ffff810013442000, task ffff81003d165860) Stack: ffff8100103bac00 ffff8100104898e8 ffff8100134436f8 ffffffff00000000 0000000000000000 ffff8100104898b0 0000000000000000 ffff810010489858 0000000000000000 ffff8100103bac00 ffff8100134436f8 ffffffff8864c634 Call Trace: [<ffffffff8864c634>] :ccm:crypto_ccm_auth+0x12d/0x140 [<ffffffff8864cf73>] :ccm:crypto_ccm_decrypt+0x161/0x23a [<ffffffff88633643>] :crypto_tester_kmod:cavs_test_rfc4309_ccm+0x4a5/0x559 [...] The above is from a RHEL5-based kernel, but upstream is susceptible too. The fix is trivial: in crypto/ccm.c:crypto_ccm_auth(), pctx->ilen contains whatever was in memory when pctx was allocated if assoclen is 0. The tested fix is to simply add an else clause setting pctx->ilen to 0 for the assoclen == 0 case, so that get_data_to_compute() doesn't try doing things its not supposed to. Signed-off-by: Jarod Wilson <jarod@redhat.com> Acked-by: Neil Horman <nhorman@tuxdriver.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2008-01-11[CRYPTO] ccm: Added CCM modeJoy Latten
This patch adds Counter with CBC-MAC (CCM) support. RFC 3610 and NIST Special Publication 800-38C were referenced. Signed-off-by: Joy Latten <latten@austin.ibm.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>