Original text:
    Clarify use of |$end0| in stitched x86-64 AES-GCM code.

    There was some uncertainty about what the code is doing with |$end0|
    and whether it was necessary for |$len| to be a multiple of 16 or 96.
    Hopefully these added comments make it clear that the code is correct
    except for the caveat regarding low memory addresses.

    Change-Id: Iea546a59dc7aeb400f50ac5d2d7b9cb88ace9027
    Reviewed-on: https://boringssl-review.googlesource.com/7194
    Reviewed-by: Adam Langley <agl@google.com>

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3700)
This commit is contained in:
Rich Salz 2017-06-14 15:07:52 -04:00
parent 0791bef0d4
commit 28f298e70a

View file

@ -116,23 +116,6 @@ _aesni_ctr32_ghash_6x:
vpxor $rndkey,$inout3,$inout3
vmovups 0x10-0x80($key),$T2 # borrow $T2 for $rndkey
vpclmulqdq \$0x01,$Hkey,$Z3,$Z2
# At this point, the current block of 96 (0x60) bytes has already been
# loaded into registers. Concurrently with processing it, we want to
# load the next 96 bytes of input for the next round. Obviously, we can
# only do this if there are at least 96 more bytes of input beyond the
# input we're currently processing, or else we'd read past the end of
# the input buffer. Here, we set |%r12| to 96 if there are at least 96
# bytes of input beyond the 96 bytes we're already processing, and we
# set |%r12| to 0 otherwise. In the case where we set |%r12| to 96,
# we'll read in the next block so that it is in registers for the next
# loop iteration. In the case where we set |%r12| to 0, we'll re-read
# the current block and then ignore what we re-read.
#
# At this point, |$in0| points to the current (already read into
# registers) block, and |$end0| points to 2*96 bytes before the end of
# the input. Thus, |$in0| > |$end0| means that we do not have the next
# 96-byte block to read in, and |$in0| <= |$end0| means we do.
xor %r12,%r12
cmp $in0,$end0
@ -426,9 +409,6 @@ $code.=<<___;
aesni_gcm_decrypt:
.cfi_startproc
xor $ret,$ret
# We call |_aesni_ctr32_ghash_6x|, which requires at least 96 (0x60)
# bytes of input.
cmp \$0x60,$len # minimal accepted length
jb .Lgcm_dec_abort
@ -490,15 +470,7 @@ $code.=<<___;
vmovdqu 0x50($inp),$Z3 # I[5]
lea ($inp),$in0
vmovdqu 0x40($inp),$Z0
# |_aesni_ctr32_ghash_6x| requires |$end0| to point to 2*96 (0xc0)
# bytes before the end of the input. Note, in particular, that this is
# correct even if |$len| is not an even multiple of 96 or 16. XXX: This
# seems to require that |$inp| + |$len| >= 2*96 (0xc0); i.e. |$inp| must
# not be near the very beginning of the address space when |$len| < 2*96
# (0xc0).
lea -0xc0($inp,$len),$end0
vmovdqu 0x30($inp),$Z1
shr \$4,$len
xor $ret,$ret
@ -663,10 +635,6 @@ _aesni_ctr32_6x:
aesni_gcm_encrypt:
.cfi_startproc
xor $ret,$ret
# We call |_aesni_ctr32_6x| twice, each call consuming 96 bytes of
# input. Then we call |_aesni_ctr32_ghash_6x|, which requires at
# least 96 more bytes of input.
cmp \$0x60*3,$len # minimal accepted length
jb .Lgcm_enc_abort
@ -723,16 +691,7 @@ $code.=<<___;
.Lenc_no_key_aliasing:
lea ($out),$in0
# |_aesni_ctr32_ghash_6x| requires |$end0| to point to 2*96 (0xc0)
# bytes before the end of the input. Note, in particular, that this is
# correct even if |$len| is not an even multiple of 96 or 16. Unlike in
# the decryption case, there's no caveat that |$out| must not be near
# the very beginning of the address space, because we know that
# |$len| >= 3*96 from the check above, and so we know
# |$out| + |$len| >= 2*96 (0xc0).
lea -0xc0($out,$len),$end0
shr \$4,$len
call _aesni_ctr32_6x