5ce12e6436
The 64-bit version can be fairly straightforwardly translated. Ironically, this makes 32-bit x86 the first architecture to meet the goal of constant-time AES-GCM given SIMD assembly. (Though x86_64 could join by simply giving up on bsaes...) Bug: 263 Change-Id: Icb2cec936457fac7132bbb5dbb094433bc14b86e Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35024 Commit-Queue: David Benjamin <davidben@google.com> Reviewed-by: Adam Langley <agl@google.com>
289 lines
9.7 KiB
Raku
289 lines
9.7 KiB
Raku
#!/usr/bin/env perl
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# Copyright (c) 2019, Google Inc.
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#
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# Permission to use, copy, modify, and/or distribute this software for any
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# purpose with or without fee is hereby granted, provided that the above
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# copyright notice and this permission notice appear in all copies.
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#
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# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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# SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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# OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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# ghash-ssse3-x86.pl is a constant-time variant of the traditional 4-bit
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# table-based GHASH implementation. It requires SSSE3 instructions.
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#
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# For background, the table-based strategy is a 4-bit windowed multiplication.
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# It precomputes all 4-bit multiples of H (this is 16 128-bit rows), then loops
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# over 4-bit windows of the input and indexes them up into the table. Visually,
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# it multiplies as in the schoolbook multiplication diagram below, but with
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# more terms. (Each term is 4 bits, so there are 32 terms in each row.) First
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# it incorporates the terms labeled '1' by indexing the most significant term
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# of X into the table. Then it shifts and repeats for '2' and so on.
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#
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# hhhhhh
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# * xxxxxx
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# ============
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# 666666
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# 555555
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# 444444
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# 333333
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# 222222
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# 111111
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#
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# This implementation changes the order. We treat the table as a 16×16 matrix
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# and transpose it. The first row is then the first byte of each multiple of H,
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# and so on. We then reorder terms as below. Observe that the terms labeled '1'
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# and '2' are all lookups into the first row, etc. This maps well to the SSSE3
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# pshufb instruction, using alternating terms of X in parallel as indices. This
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# alternation is needed because pshufb maps 4 bits to 8 bits. Then we shift and
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# repeat for each row.
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#
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# hhhhhh
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# * xxxxxx
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# ============
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# 224466
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# 113355
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# 224466
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# 113355
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# 224466
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# 113355
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#
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# Next we account for GCM's confusing bit order. The "first" bit is the least
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# significant coefficient, but GCM treats the most sigificant bit within a byte
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# as first. Bytes are little-endian, and bits are big-endian. We reverse the
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# bytes in XMM registers for a consistent bit and byte ordering, but this means
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# the least significant bit is the most significant coefficient and vice versa.
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#
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# For consistency, "low", "high", "left-shift", and "right-shift" refer to the
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# bit ordering within the XMM register, rather than the reversed coefficient
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# ordering. Low bits are less significant bits and more significant
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# coefficients. Right-shifts move from MSB to the LSB and correspond to
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# increasing the power of each coefficient.
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#
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# Note this bit reversal enters into the table's column indices. H*1 is stored
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# in column 0b1000 and H*x^3 is stored in column 0b0001. It also means earlier
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# table rows contain more significant coefficients, so we iterate forwards.
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$0 =~ m/(.*[\/\\])[^\/\\]+$/; $dir=$1;
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push(@INC,"${dir}","${dir}../../../perlasm");
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require "x86asm.pl";
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$output = pop;
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open STDOUT, ">$output";
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&asm_init($ARGV[0]);
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my ($Xi, $Htable, $in, $len) = ("edi", "esi", "edx", "ecx");
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&static_label("reverse_bytes");
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&static_label("low4_mask");
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my $call_counter = 0;
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# process_rows emits assembly code to process $rows rows of the table. On
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# input, $Htable stores the pointer to the next row. xmm0 and xmm1 store the
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# low and high halves of the input. The result so far is passed in xmm2. xmm3
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# must be zero. On output, $Htable is advanced to the next row and xmm2 is
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# updated. xmm3 remains zero. It clobbers eax, xmm4, xmm5, and xmm6.
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sub process_rows {
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my ($rows) = @_;
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$call_counter++;
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# Shifting whole XMM registers by bits is complex. psrldq shifts by
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# bytes, and psrlq shifts the two 64-bit halves separately. Each row
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# produces 8 bits of carry, and the reduction needs an additional 7-bit
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# shift. This must fit in 64 bits so reduction can use psrlq. This
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# allows up to 7 rows at a time.
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die "Carry register would overflow 64 bits." if ($rows*8 + 7 > 64);
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&mov("eax", $rows);
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&set_label("loop_row_$call_counter");
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&movdqa("xmm4", &QWP(0, $Htable));
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&lea($Htable, &DWP(16, $Htable));
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# Right-shift xmm2 and xmm3 by 8 bytes.
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&movdqa("xmm6", "xmm2");
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&palignr("xmm6", "xmm3", 1);
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&movdqa("xmm3", "xmm6");
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&psrldq("xmm2", 1);
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# Load the next table row and index the low and high bits of the input.
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# Note the low (respectively, high) half corresponds to more
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# (respectively, less) significant coefficients.
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&movdqa("xmm5", "xmm4");
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&pshufb("xmm4", "xmm0");
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&pshufb("xmm5", "xmm1");
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# Add the high half (xmm5) without shifting.
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&pxor("xmm2", "xmm5");
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# Add the low half (xmm4). This must be right-shifted by 4 bits. First,
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# add into the carry register (xmm3).
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&movdqa("xmm5", "xmm4");
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&psllq("xmm5", 60);
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&movdqa("xmm6", "xmm5");
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&pslldq("xmm6", 8);
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&pxor("xmm3", "xmm6");
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# Next, add into xmm2.
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&psrldq("xmm5", 8);
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&pxor("xmm2", "xmm5");
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&psrlq("xmm4", 4);
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&pxor("xmm2", "xmm4");
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&sub("eax", 1);
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&jnz(&label("loop_row_$call_counter"));
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# Reduce the carry register. The reduction polynomial is 1 + x + x^2 +
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# x^7, so we shift and XOR four times.
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&pxor("xmm2", "xmm3"); # x^0 = 0
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&psrlq("xmm3", 1);
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&pxor("xmm2", "xmm3"); # x^1 = x
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&psrlq("xmm3", 1);
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&pxor("xmm2", "xmm3"); # x^(1+1) = x^2
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&psrlq("xmm3", 5);
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&pxor("xmm2", "xmm3"); # x^(1+1+5) = x^7
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&pxor("xmm3", "xmm3");
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____
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}
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# gcm_gmult_ssse3 multiplies |Xi| by |Htable| and writes the result to |Xi|.
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# |Xi| is represented in GHASH's serialized byte representation. |Htable| is
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# formatted as described above.
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# void gcm_gmult_ssse3(uint64_t Xi[2], const u128 Htable[16]);
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&function_begin("gcm_gmult_ssse3");
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&mov($Xi, &wparam(0));
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&mov($Htable, &wparam(1));
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&movdqu("xmm0", &QWP(0, $Xi));
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&call(&label("pic_point"));
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&set_label("pic_point");
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&blindpop("eax");
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&movdqa("xmm7", &QWP(&label("reverse_bytes")."-".&label("pic_point"), "eax"));
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&movdqa("xmm2", &QWP(&label("low4_mask")."-".&label("pic_point"), "eax"));
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# Reverse input bytes to deserialize.
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&pshufb("xmm0", "xmm7");
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# Split each byte into low (xmm0) and high (xmm1) halves.
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&movdqa("xmm1", "xmm2");
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&pandn("xmm1", "xmm0");
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&psrld("xmm1", 4);
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&pand("xmm0", "xmm2");
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# Maintain the result in xmm2 (the value) and xmm3 (carry bits). Note
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# that, due to bit reversal, xmm3 contains bits that fall off when
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# right-shifting, not left-shifting.
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&pxor("xmm2", "xmm2");
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&pxor("xmm3", "xmm3");
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# We must reduce at least once every 7 rows, so divide into three
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# chunks.
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&process_rows(5);
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&process_rows(5);
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&process_rows(6);
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# Store the result. Reverse bytes to serialize.
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&pshufb("xmm2", "xmm7");
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&movdqu(&QWP(0, $Xi), "xmm2");
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# Zero any registers which contain secrets.
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&pxor("xmm0", "xmm0");
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&pxor("xmm1", "xmm1");
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&pxor("xmm2", "xmm2");
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&pxor("xmm3", "xmm3");
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&pxor("xmm4", "xmm4");
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&pxor("xmm5", "xmm5");
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&pxor("xmm6", "xmm6");
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&function_end("gcm_gmult_ssse3");
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# gcm_ghash_ssse3 incorporates |len| bytes from |in| to |Xi|, using |Htable| as
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# the key. It writes the result back to |Xi|. |Xi| is represented in GHASH's
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# serialized byte representation. |Htable| is formatted as described above.
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# void gcm_ghash_ssse3(uint64_t Xi[2], const u128 Htable[16], const uint8_t *in,
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# size_t len);
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&function_begin("gcm_ghash_ssse3");
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&mov($Xi, &wparam(0));
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&mov($Htable, &wparam(1));
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&mov($in, &wparam(2));
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&mov($len, &wparam(3));
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&movdqu("xmm0", &QWP(0, $Xi));
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&call(&label("pic_point"));
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&set_label("pic_point");
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&blindpop("ebx");
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&movdqa("xmm7", &QWP(&label("reverse_bytes")."-".&label("pic_point"), "ebx"));
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# This function only processes whole blocks.
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&and($len, -16);
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# Reverse input bytes to deserialize. We maintain the running
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# total in xmm0.
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&pshufb("xmm0", "xmm7");
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# Iterate over each block. On entry to each iteration, xmm3 is zero.
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&pxor("xmm3", "xmm3");
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&set_label("loop_ghash");
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&movdqa("xmm2", &QWP(&label("low4_mask")."-".&label("pic_point"), "ebx"));
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# Incorporate the next block of input.
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&movdqu("xmm1", &QWP(0, $in));
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&pshufb("xmm1", "xmm7"); # Reverse bytes.
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&pxor("xmm0", "xmm1");
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# Split each byte into low (xmm0) and high (xmm1) halves.
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&movdqa("xmm1", "xmm2");
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&pandn("xmm1", "xmm0");
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&psrld("xmm1", 4);
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&pand("xmm0", "xmm2");
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# Maintain the result in xmm2 (the value) and xmm3 (carry bits). Note
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# that, due to bit reversal, xmm3 contains bits that fall off when
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# right-shifting, not left-shifting.
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&pxor("xmm2", "xmm2");
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# xmm3 is already zero at this point.
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# We must reduce at least once every 7 rows, so divide into three
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# chunks.
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&process_rows(5);
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&process_rows(5);
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&process_rows(6);
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&movdqa("xmm0", "xmm2");
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# Rewind $Htable for the next iteration.
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&lea($Htable, &DWP(-256, $Htable));
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# Advance input and continue.
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&lea($in, &DWP(16, $in));
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&sub($len, 16);
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&jnz(&label("loop_ghash"));
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# Reverse bytes and store the result.
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&pshufb("xmm0", "xmm7");
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&movdqu(&QWP(0, $Xi), "xmm0");
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# Zero any registers which contain secrets.
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&pxor("xmm0", "xmm0");
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&pxor("xmm1", "xmm1");
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&pxor("xmm2", "xmm2");
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&pxor("xmm3", "xmm3");
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&pxor("xmm4", "xmm4");
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&pxor("xmm5", "xmm5");
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&pxor("xmm6", "xmm6");
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&function_end("gcm_ghash_ssse3");
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# reverse_bytes is a permutation which, if applied with pshufb, reverses the
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# bytes in an XMM register.
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&set_label("reverse_bytes", 16);
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&data_byte(15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0);
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# low4_mask is an XMM mask which selects the low four bits of each byte.
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&set_label("low4_mask", 16);
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&data_word(0x0f0f0f0f, 0x0f0f0f0f, 0x0f0f0f0f, 0x0f0f0f0f);
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&asm_finish();
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close STDOUT;
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