Undo commit cd359b2

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)

1 files changed, 0 insertions, 41 deletions

diff --git a/crypto/modes/asm/aesni-gcm-x86_64.pl b/crypto/modes/asm/aesni-gcm-x86_64.pl
index 5e69cb86fa..3cd231e22f 100644
--- a/crypto/modes/asm/aesni-gcm-x86_64.pl
+++ b/crypto/modes/asm/aesni-gcm-x86_64.pl
@@ -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