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#!/usr/bin/env perl
# Copyright (c) 2019, Google Inc.
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
# SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
# OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
# ghash-ssse3-x86_64.pl is a constant-time variant of the traditional 4-bit
# table-based GHASH implementation. It requires SSSE3 instructions.
#
# For background, the table-based strategy is a 4-bit windowed multiplication.
# It precomputes all 4-bit multiples of H (this is 16 128-bit rows), then loops
# over 4-bit windows of the input and indexes them up into the table. Visually,
# it multiplies as in the schoolbook multiplication diagram below, but with
# more terms. (Each term is 4 bits, so there are 32 terms in each row.) First
# it incorporates the terms labeled '1' by indexing the most significant term
# of X into the table. Then it shifts and repeats for '2' and so on.
#
# hhhhhh
# * xxxxxx
# ============
# 666666
# 555555
# 444444
# 333333
# 222222
# 111111
#
# This implementation changes the order. We treat the table as a 16×16 matrix
# and transpose it. The first row is then the first byte of each multiple of H,
# and so on. We then reorder terms as below. Observe that the terms labeled '1'
# and '2' are all lookups into the first row, etc. This maps well to the SSSE3
# pshufb instruction, using alternating terms of X in parallel as indices. This
# alternation is needed because pshufb maps 4 bits to 8 bits. Then we shift and
# repeat for each row.
#
# hhhhhh
# * xxxxxx
# ============
# 224466
# 113355
# 224466
# 113355
# 224466
# 113355
#
# Next we account for GCM's confusing bit order. The "first" bit is the least
# significant coefficient, but GCM treats the most sigificant bit within a byte
# as first. Bytes are little-endian, and bits are big-endian. We reverse the
# bytes in XMM registers for a consistent bit and byte ordering, but this means
# the least significant bit is the most significant coefficient and vice versa.
#
# For consistency, "low", "high", "left-shift", and "right-shift" refer to the
# bit ordering within the XMM register, rather than the reversed coefficient
# ordering. Low bits are less significant bits and more significant
# coefficients. Right-shifts move from MSB to the LSB and correspond to
# increasing the power of each coefficient.
#
# Note this bit reversal enters into the table's column indices. H*1 is stored
# in column 0b1000 and H*x^3 is stored in column 0b0001. It also means earlier
# table rows contain more significant coefficients, so we iterate forwards.
use strict;
my $flavour = shift;
my $output = shift;
if ($flavour =~ /\./) { $output = $flavour; undef $flavour; }
my $win64 = 0;
$win64 = 1 if ($flavour =~ /[nm]asm|mingw64/ || $output =~ /\.asm$/);
$0 =~ m/(.*[\/\\])[^\/\\]+$/;
my $dir = $1;
my $xlate;
( $xlate="${dir}x86_64-xlate.pl" and -f $xlate ) or
( $xlate="${dir}../../../perlasm/x86_64-xlate.pl" and -f $xlate) or
die "can't locate x86_64-xlate.pl";
open OUT, "| \"$^X\" \"$xlate\" $flavour \"$output\"";
*STDOUT = *OUT;
my ($Xi, $Htable, $in, $len) = $win64 ? ("%rcx", "%rdx", "%r8", "%r9") :
("%rdi", "%rsi", "%rdx", "%rcx");
my $code = <<____;
.text
# gcm_gmult_ssse3 multiplies |Xi| by |Htable| and writes the result to |Xi|.
# |Xi| is represented in GHASH's serialized byte representation. |Htable| is
# formatted as described above.
# void gcm_gmult_ssse3(uint64_t Xi[2], const u128 Htable[16]);
.type gcm_gmult_ssse3, \@abi-omnipotent
.globl gcm_gmult_ssse3
.align 16
gcm_gmult_ssse3:
.cfi_startproc
.Lgmult_seh_begin:
____
$code .= <<____ if ($win64);
subq \$40, %rsp
.Lgmult_seh_allocstack:
movdqa %xmm6, (%rsp)
.Lgmult_seh_save_xmm6:
movdqa %xmm10, 16(%rsp)
.Lgmult_seh_save_xmm10:
.Lgmult_seh_prolog_end:
____
$code .= <<____;
movdqu ($Xi), %xmm0
movdqa .Lreverse_bytes(%rip), %xmm10
movdqa .Llow4_mask(%rip), %xmm2
# Reverse input bytes to deserialize.
pshufb %xmm10, %xmm0
# Split each byte into low (%xmm0) and high (%xmm1) halves.
movdqa %xmm2, %xmm1
pandn %xmm0, %xmm1
psrld \$4, %xmm1
pand %xmm2, %xmm0
# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
# that, due to bit reversal, %xmm3 contains bits that fall off when
# right-shifting, not left-shifting.
pxor %xmm2, %xmm2
pxor %xmm3, %xmm3
____
my $call_counter = 0;
# process_rows returns assembly code to process $rows rows of the table. On
# input, $Htable stores the pointer to the next row. %xmm0 and %xmm1 store the
# low and high halves of the input. The result so far is passed in %xmm2. %xmm3
# must be zero. On output, $Htable is advanced to the next row and %xmm2 is
# updated. %xmm3 remains zero. It clobbers %rax, %xmm4, %xmm5, and %xmm6.
sub process_rows {
my ($rows) = @_;
$call_counter++;
# Shifting whole XMM registers by bits is complex. psrldq shifts by bytes,
# and psrlq shifts the two 64-bit halves separately. Each row produces 8
# bits of carry, and the reduction needs an additional 7-bit shift. This
# must fit in 64 bits so reduction can use psrlq. This allows up to 7 rows
# at a time.
die "Carry register would overflow 64 bits." if ($rows*8 + 7 > 64);
return <<____;
movq \$$rows, %rax
.Loop_row_$call_counter:
movdqa ($Htable), %xmm4
leaq 16($Htable), $Htable
# Right-shift %xmm2 and %xmm3 by 8 bytes.
movdqa %xmm2, %xmm6
palignr \$1, %xmm3, %xmm6
movdqa %xmm6, %xmm3
psrldq \$1, %xmm2
# Load the next table row and index the low and high bits of the input.
# Note the low (respectively, high) half corresponds to more
# (respectively, less) significant coefficients.
movdqa %xmm4, %xmm5
pshufb %xmm0, %xmm4
pshufb %xmm1, %xmm5
# Add the high half (%xmm5) without shifting.
pxor %xmm5, %xmm2
# Add the low half (%xmm4). This must be right-shifted by 4 bits. First,
# add into the carry register (%xmm3).
movdqa %xmm4, %xmm5
psllq \$60, %xmm5
movdqa %xmm5, %xmm6
pslldq \$8, %xmm6
pxor %xmm6, %xmm3
# Next, add into %xmm2.
psrldq \$8, %xmm5
pxor %xmm5, %xmm2
psrlq \$4, %xmm4
pxor %xmm4, %xmm2
subq \$1, %rax
jnz .Loop_row_$call_counter
# Reduce the carry register. The reduction polynomial is 1 + x + x^2 +
# x^7, so we shift and XOR four times.
pxor %xmm3, %xmm2 # x^0 = 0
psrlq \$1, %xmm3
pxor %xmm3, %xmm2 # x^1 = x
psrlq \$1, %xmm3
pxor %xmm3, %xmm2 # x^(1+1) = x^2
psrlq \$5, %xmm3
pxor %xmm3, %xmm2 # x^(1+1+5) = x^7
pxor %xmm3, %xmm3
____
}
# We must reduce at least once every 7 rows, so divide into three chunks.
$code .= process_rows(5);
$code .= process_rows(5);
$code .= process_rows(6);
$code .= <<____;
# Store the result. Reverse bytes to serialize.
pshufb %xmm10, %xmm2
movdqu %xmm2, ($Xi)
# Zero any registers which contain secrets.
pxor %xmm0, %xmm0
pxor %xmm1, %xmm1
pxor %xmm2, %xmm2
pxor %xmm3, %xmm3
pxor %xmm4, %xmm4
pxor %xmm5, %xmm5
pxor %xmm6, %xmm6
____
$code .= <<____ if ($win64);
movdqa (%rsp), %xmm6
movdqa 16(%rsp), %xmm10
addq \$40, %rsp
____
$code .= <<____;
ret
.Lgmult_seh_end:
.cfi_endproc
.size gcm_gmult_ssse3,.-gcm_gmult_ssse3
____
$code .= <<____;
# gcm_ghash_ssse3 incorporates |len| bytes from |in| to |Xi|, using |Htable| as
# the key. It writes the result back to |Xi|. |Xi| is represented in GHASH's
# serialized byte representation. |Htable| is formatted as described above.
# void gcm_ghash_ssse3(uint64_t Xi[2], const u128 Htable[16], const uint8_t *in,
# size_t len);
.type gcm_ghash_ssse3, \@abi-omnipotent
.globl gcm_ghash_ssse3
.align 16
gcm_ghash_ssse3:
.Lghash_seh_begin:
.cfi_startproc
____
$code .= <<____ if ($win64);
subq \$56, %rsp
.Lghash_seh_allocstack:
movdqa %xmm6, (%rsp)
.Lghash_seh_save_xmm6:
movdqa %xmm10, 16(%rsp)
.Lghash_seh_save_xmm10:
movdqa %xmm11, 32(%rsp)
.Lghash_seh_save_xmm11:
.Lghash_seh_prolog_end:
____
$code .= <<____;
movdqu ($Xi), %xmm0
movdqa .Lreverse_bytes(%rip), %xmm10
movdqa .Llow4_mask(%rip), %xmm11
# This function only processes whole blocks.
andq \$-16, $len
# Reverse input bytes to deserialize. We maintain the running
# total in %xmm0.
pshufb %xmm10, %xmm0
# Iterate over each block. On entry to each iteration, %xmm3 is zero.
pxor %xmm3, %xmm3
.Loop_ghash:
# Incorporate the next block of input.
movdqu ($in), %xmm1
pshufb %xmm10, %xmm1 # Reverse bytes.
pxor %xmm1, %xmm0
# Split each byte into low (%xmm0) and high (%xmm1) halves.
movdqa %xmm11, %xmm1
pandn %xmm0, %xmm1
psrld \$4, %xmm1
pand %xmm11, %xmm0
# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
# that, due to bit reversal, %xmm3 contains bits that fall off when
# right-shifting, not left-shifting.
pxor %xmm2, %xmm2
# %xmm3 is already zero at this point.
____
# We must reduce at least once every 7 rows, so divide into three chunks.
$code .= process_rows(5);
$code .= process_rows(5);
$code .= process_rows(6);
$code .= <<____;
movdqa %xmm2, %xmm0
# Rewind $Htable for the next iteration.
leaq -256($Htable), $Htable
# Advance input and continue.
leaq 16($in), $in
subq \$16, $len
jnz .Loop_ghash
# Reverse bytes and store the result.
pshufb %xmm10, %xmm0
movdqu %xmm0, ($Xi)
# Zero any registers which contain secrets.
pxor %xmm0, %xmm0
pxor %xmm1, %xmm1
pxor %xmm2, %xmm2
pxor %xmm3, %xmm3
pxor %xmm4, %xmm4
pxor %xmm5, %xmm5
pxor %xmm6, %xmm6
____
$code .= <<____ if ($win64);
movdqa (%rsp), %xmm6
movdqa 16(%rsp), %xmm10
movdqa 32(%rsp), %xmm11
addq \$56, %rsp
____
$code .= <<____;
ret
.Lghash_seh_end:
.cfi_endproc
.size gcm_ghash_ssse3,.-gcm_ghash_ssse3
.align 16
# .Lreverse_bytes is a permutation which, if applied with pshufb, reverses the
# bytes in an XMM register.
.Lreverse_bytes:
.byte 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
# .Llow4_mask is an XMM mask which selects the low four bits of each byte.
.Llow4_mask:
.quad 0x0f0f0f0f0f0f0f0f, 0x0f0f0f0f0f0f0f0f
____
if ($win64) {
# Add unwind metadata for SEH.
#
# TODO(davidben): This is all manual right now. Once we've added SEH tests,
# add support for emitting these in x86_64-xlate.pl, probably based on MASM
# and Yasm's unwind directives, and unify with CFI. Then upstream it to
# replace the error-prone and non-standard custom handlers.
# See https://docs.microsoft.com/en-us/cpp/build/struct-unwind-code?view=vs-2017
my $UWOP_ALLOC_SMALL = 2;
my $UWOP_SAVE_XMM128 = 8;
$code .= <<____;
.section .pdata
.align 4
.rva .Lgmult_seh_begin
.rva .Lgmult_seh_end
.rva .Lgmult_seh_info
.rva .Lghash_seh_begin
.rva .Lghash_seh_end
.rva .Lghash_seh_info
.section .xdata
.align 8
.Lgmult_seh_info:
.byte 1 # version 1, no flags
.byte .Lgmult_seh_prolog_end-.Lgmult_seh_begin
.byte 5 # num_slots = 1 + 2 + 2
.byte 0 # no frame register
.byte .Lgmult_seh_allocstack-.Lgmult_seh_begin
.byte @{[$UWOP_ALLOC_SMALL | (((40 - 8) / 8) << 4)]}
.byte .Lgmult_seh_save_xmm6-.Lgmult_seh_begin
.byte @{[$UWOP_SAVE_XMM128 | (6 << 4)]}
.value 0
.byte .Lgmult_seh_save_xmm10-.Lgmult_seh_begin
.byte @{[$UWOP_SAVE_XMM128 | (10 << 4)]}
.value 1
.align 8
.Lghash_seh_info:
.byte 1 # version 1, no flags
.byte .Lghash_seh_prolog_end-.Lghash_seh_begin
.byte 7 # num_slots = 1 + 2 + 2 + 2
.byte 0 # no frame register
.byte .Lghash_seh_allocstack-.Lghash_seh_begin
.byte @{[$UWOP_ALLOC_SMALL | (((56 - 8) / 8) << 4)]}
.byte .Lghash_seh_save_xmm6-.Lghash_seh_begin
.byte @{[$UWOP_SAVE_XMM128 | (6 << 4)]}
.value 0
.byte .Lghash_seh_save_xmm10-.Lghash_seh_begin
.byte @{[$UWOP_SAVE_XMM128 | (10 << 4)]}
.value 1
.byte .Lghash_seh_save_xmm11-.Lghash_seh_begin
.byte @{[$UWOP_SAVE_XMM128 | (11 << 4)]}
.value 2
____
}
print $code;
close STDOUT;