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passt/checksum.c

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// SPDX-License-Identifier: GPL-2.0-or-later AND BSD-3-Clause
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* checksum.c - TCP/IP checksum routines
*
* Copyright (c) 2021 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*
* This file also contains code originally licensed under the following terms:
*
* Copyright (c) 2014-2016, The Regents of the University of California.
* Copyright (c) 2016-2017, Nefeli Networks, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the names of the copyright holders nor the names of their
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* See the comment to csum_avx2() for further details.
*/
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <netinet/ip_icmp.h>
#include <stddef.h>
#include <stdint.h>
#include <linux/udp.h>
#include <linux/icmpv6.h>
#include "util.h"
#include "ip.h"
#include "checksum.h"
/* Checksums are optional for UDP over IPv4, so we usually just set
* them to 0. Change this to 1 to calculate real UDP over IPv4
* checksums
*/
#define UDP4_REAL_CHECKSUMS 0
/**
* sum_16b() - Calculate sum of 16-bit words
* @buf: Input buffer
* @len: Buffer length
*
* Return: 32-bit sum of 16-bit words
*/
/* Type-Based Alias Analysis (TBAA) optimisation in gcc 11 and 12 (-flto -O2)
* makes these functions essentially useless by allowing reordering of stores of
* input data across function calls. Not even declaring @in as char pointer is
* enough: disable gcc's interpretation of strict aliasing altogether. See also:
*
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106706
* https://stackoverflow.com/questions/2958633/gcc-strict-aliasing-and-horror-stories
* https://lore.kernel.org/all/alpine.LFD.2.00.0901121128080.6528__33422.5328093909$1232291247$gmane$org@localhost.localdomain/
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
__attribute__((optimize("-fno-strict-aliasing")))
uint32_t sum_16b(const void *buf, size_t len)
{
const uint16_t *p = buf;
uint32_t sum = 0;
while (len > 1) {
sum += *p++;
len -= 2;
}
if (len > 0)
sum += *p & htons(0xff00);
return sum;
}
/**
* csum_fold() - Fold long sum for IP and TCP checksum
* @sum: Original long sum
*
* Return: 16-bit folded sum
*/
uint16_t csum_fold(uint32_t sum)
{
while (sum >> 16)
sum = (sum & 0xffff) + (sum >> 16);
return sum;
}
/**
* csum_ip4_header() - Calculate IPv4 header checksum
* @tot_len: IPv4 payload length (data + IP header, network order)
* @protocol: Protocol number (network order)
* @saddr: IPv4 source address (network order)
* @daddr: IPv4 destination address (network order)
*
* Return: 16-bit folded sum of the IPv4 header
*/
uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
struct in_addr saddr, struct in_addr daddr)
{
uint32_t sum = L2_BUF_IP4_PSUM(protocol);
sum += tot_len;
sum += (saddr.s_addr >> 16) & 0xffff;
sum += saddr.s_addr & 0xffff;
sum += (daddr.s_addr >> 16) & 0xffff;
sum += daddr.s_addr & 0xffff;
return ~csum_fold(sum);
}
/**
* proto_ipv4_header_psum() - Calculates the partial checksum of an
* IPv4 header for UDP or TCP
* @tot_len: IPv4 Payload length (host order)
* @proto: Protocol number (host order)
* @saddr: Source address (network order)
* @daddr: Destination address (network order)
* Returns: Partial checksum of the IPv4 header
*/
uint32_t proto_ipv4_header_psum(uint16_t tot_len, uint8_t protocol,
struct in_addr saddr, struct in_addr daddr)
{
uint32_t psum = htons(protocol);
psum += (saddr.s_addr >> 16) & 0xffff;
psum += saddr.s_addr & 0xffff;
psum += (daddr.s_addr >> 16) & 0xffff;
psum += daddr.s_addr & 0xffff;
psum += htons(tot_len);
return psum;
}
/**
* csum_udp4() - Calculate and set checksum for a UDP over IPv4 packet
* @udp4hr: UDP header, initialised apart from checksum
* @saddr: IPv4 source address
* @daddr: IPv4 destination address
* @payload: ICMPv4 packet payload
* @len: Length of @payload (not including UDP)
*/
void csum_udp4(struct udphdr *udp4hr,
struct in_addr saddr, struct in_addr daddr,
const void *payload, size_t len)
{
/* UDP checksums are optional, so don't bother */
udp4hr->check = 0;
if (UDP4_REAL_CHECKSUMS) {
uint16_t tot_len = len + sizeof(struct udphdr);
uint32_t psum = proto_ipv4_header_psum(tot_len, IPPROTO_UDP,
saddr, daddr);
psum = csum_unfolded(udp4hr, sizeof(struct udphdr), psum);
udp4hr->check = csum(payload, len, psum);
}
}
/**
* csum_icmp4() - Calculate and set checksum for an ICMP packet
* @icmp4hr: ICMP header, initialised apart from checksum
* @payload: ICMP packet payload
* @len: Length of @payload (not including ICMP header)
*/
void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t len)
{
uint32_t psum;
icmp4hr->checksum = 0;
/* Partial checksum for ICMP header alone */
psum = sum_16b(icmp4hr, sizeof(*icmp4hr));
icmp4hr->checksum = csum(payload, len, psum);
}
/**
* proto_ipv6_header_psum() - Calculates the partial checksum of an
* IPv6 header for UDP or TCP
* @payload_len: IPv6 payload length (host order)
* @proto: Protocol number (host order)
* @saddr: Source address (network order)
* @daddr: Destination address (network order)
* Returns: Partial checksum of the IPv6 header
*/
uint32_t proto_ipv6_header_psum(uint16_t payload_len, uint8_t protocol,
const struct in6_addr *saddr,
const struct in6_addr *daddr)
{
uint32_t sum = htons(protocol) + htons(payload_len);
sum += sum_16b(saddr, sizeof(*saddr));
sum += sum_16b(daddr, sizeof(*daddr));
return sum;
}
/**
* csum_udp6() - Calculate and set checksum for a UDP over IPv6 packet
* @udp6hr: UDP header, initialised apart from checksum
* @payload: UDP packet payload
* @len: Length of @payload (not including UDP header)
*/
void csum_udp6(struct udphdr *udp6hr,
const struct in6_addr *saddr, const struct in6_addr *daddr,
const void *payload, size_t len)
{
uint32_t psum = proto_ipv6_header_psum(len + sizeof(struct udphdr),
IPPROTO_UDP, saddr, daddr);
udp6hr->check = 0;
psum = csum_unfolded(udp6hr, sizeof(struct udphdr), psum);
udp6hr->check = csum(payload, len, psum);
}
/**
* csum_icmp6() - Calculate and set checksum for an ICMPv6 packet
* @icmp6hr: ICMPv6 header, initialised apart from checksum
* @saddr: IPv6 source address
* @daddr: IPv6 destination address
* @payload: ICMP packet payload
* @len: Length of @payload (not including ICMPv6 header)
*/
void csum_icmp6(struct icmp6hdr *icmp6hr,
const struct in6_addr *saddr, const struct in6_addr *daddr,
const void *payload, size_t len)
{
/* Partial checksum for the pseudo-IPv6 header */
uint32_t psum = sum_16b(saddr, sizeof(*saddr)) +
sum_16b(daddr, sizeof(*daddr)) +
htons(len + sizeof(*icmp6hr)) + htons(IPPROTO_ICMPV6);
icmp6hr->icmp6_cksum = 0;
/* Add in partial checksum for the ICMPv6 header alone */
psum += sum_16b(icmp6hr, sizeof(*icmp6hr));
icmp6hr->icmp6_cksum = csum(payload, len, psum);
}
#ifdef __AVX2__
#include <immintrin.h>
/**
* csum_avx2() - Compute 32-bit checksum using AVX2 SIMD instructions
* @buf: Input buffer, must be aligned to 32-byte boundary
* @len: Input length
* @init: Initial 32-bit checksum, 0 for no pre-computed checksum
*
* Return: 32-bit checksum, not complemented, not folded
*
* This implementation is mostly sourced from BESS ("Berkeley Extensible
* Software Switch"), core/utils/checksum.h, distributed under the terms of the
* 3-Clause BSD license. Notable changes:
* - input buffer data is loaded (streamed) with a non-temporal aligned hint
* (VMOVNTDQA, _mm256_stream_load_si256() intrinsic) instead of the original
* unaligned load with temporal hint (VMOVDQU, _mm256_loadu_si256() intrinsic)
* given that the input buffer layout guarantees 32-byte alignment of TCP and
* UDP headers, and that the data is not used immediately afterwards, reducing
* cache pollution significantly and latency (e.g. on Intel Skylake: 0 instead
* of 7)
* - read from four streams in parallel as long as we have more than 128 bytes,
* not just two
* - replace the ADCQ implementation for the portion remaining after the
* checksum computation for 128-byte blocks by a load/unpack/add loop on a
* single stream, and do the rest with a for loop, auto-vectorisation seems to
* outperforms the original hand-coded loop there
* - sum_a/sum_b unpacking is interleaved and not sequential to reduce stalls
* - coding style adaptation
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
static uint32_t csum_avx2(const void *buf, size_t len, uint32_t init)
{
__m256i a, b, sum256, sum_a_hi, sum_a_lo, sum_b_hi, sum_b_lo, c, d;
__m256i __sum_a_hi, __sum_a_lo, __sum_b_hi, __sum_b_lo;
const __m256i *buf256 = (const __m256i *)buf;
const uint64_t *buf64;
const uint16_t *buf16;
uint64_t sum64 = init;
int odd = len & 1;
__m128i sum128;
__m256i zero;
zero = _mm256_setzero_si256();
if (len < sizeof(__m256i) * 4)
goto less_than_128_bytes;
/* We parallelize two ymm streams to minimize register dependency:
*
* a: buf256, buf256 + 2, ...
* b: buf256 + 1, buf256 + 3, ...
*/
a = _mm256_stream_load_si256(buf256);
b = _mm256_stream_load_si256(buf256 + 1);
/* For each stream, accumulate unpackhi and unpacklo in parallel (as
* 4x64bit vectors, so that each upper 0000 can hold carries):
*
* 32B data: aaaaAAAA bbbbBBBB ccccCCCC ddddDDDD (1 letter: 1 byte)
* unpackhi: bbbb0000 BBBB0000 dddd0000 DDDD0000
* unpacklo: aaaa0000 AAAA0000 cccc0000 CCCC0000
*/
sum_a_hi = _mm256_unpackhi_epi32(a, zero);
sum_b_hi = _mm256_unpackhi_epi32(b, zero);
sum_a_lo = _mm256_unpacklo_epi32(a, zero);
sum_b_lo = _mm256_unpacklo_epi32(b, zero);
len -= sizeof(__m256i) * 2;
buf256 += 2;
/* As long as we have more than 128 bytes, (stream) load from four
* streams instead of two, interleaving loads and register usage, to
* further decrease stalls, but don't double the number of accumulators
* and don't make this a general case to keep branching reasonable.
*/
if (len >= sizeof(a) * 4) {
a = _mm256_stream_load_si256(buf256);
b = _mm256_stream_load_si256(buf256 + 1);
c = _mm256_stream_load_si256(buf256 + 2);
d = _mm256_stream_load_si256(buf256 + 3);
}
for (; len >= sizeof(a) * 4; len -= sizeof(a) * 4, buf256 += 4) {
__sum_a_hi = _mm256_add_epi64(sum_a_hi,
_mm256_unpackhi_epi32(a, zero));
__sum_b_hi = _mm256_add_epi64(sum_b_hi,
_mm256_unpackhi_epi32(b, zero));
__sum_a_lo = _mm256_add_epi64(sum_a_lo,
_mm256_unpacklo_epi32(a, zero));
__sum_b_lo = _mm256_add_epi64(sum_b_lo,
_mm256_unpacklo_epi32(b, zero));
if (len >= sizeof(a) * 8) {
a = _mm256_stream_load_si256(buf256 + 4);
b = _mm256_stream_load_si256(buf256 + 5);
}
sum_a_hi = _mm256_add_epi64(__sum_a_hi,
_mm256_unpackhi_epi32(c, zero));
sum_b_hi = _mm256_add_epi64(__sum_b_hi,
_mm256_unpackhi_epi32(d, zero));
sum_a_lo = _mm256_add_epi64(__sum_a_lo,
_mm256_unpacklo_epi32(c, zero));
sum_b_lo = _mm256_add_epi64(__sum_b_lo,
_mm256_unpacklo_epi32(d, zero));
if (len >= sizeof(a) * 8) {
c = _mm256_stream_load_si256(buf256 + 6);
d = _mm256_stream_load_si256(buf256 + 7);
}
}
for (; len >= sizeof(a) * 2; len -= sizeof(a) * 2, buf256 += 2) {
a = _mm256_stream_load_si256(buf256);
b = _mm256_stream_load_si256(buf256 + 1);
sum_a_hi = _mm256_add_epi64(sum_a_hi,
_mm256_unpackhi_epi32(a, zero));
sum_b_hi = _mm256_add_epi64(sum_b_hi,
_mm256_unpackhi_epi32(b, zero));
sum_a_lo = _mm256_add_epi64(sum_a_lo,
_mm256_unpacklo_epi32(a, zero));
sum_b_lo = _mm256_add_epi64(sum_b_lo,
_mm256_unpacklo_epi32(b, zero));
}
/* Fold four 256bit sums into one 128-bit sum. */
sum256 = _mm256_add_epi64(_mm256_add_epi64(sum_a_hi, sum_b_lo),
_mm256_add_epi64(sum_b_hi, sum_a_lo));
sum128 = _mm_add_epi64(_mm256_extracti128_si256(sum256, 0),
_mm256_extracti128_si256(sum256, 1));
/* Fold 128-bit sum into 64 bits. */
sum64 += _mm_extract_epi64(sum128, 0) + _mm_extract_epi64(sum128, 1);
less_than_128_bytes:
for (; len >= sizeof(a); len -= sizeof(a), buf256++) {
a = _mm256_stream_load_si256(buf256);
sum_a_hi = _mm256_unpackhi_epi32(a, zero);
sum_a_lo = _mm256_unpacklo_epi32(a, zero);
sum256 = _mm256_add_epi64(sum_a_hi, sum_a_lo);
sum128 = _mm_add_epi64(_mm256_extracti128_si256(sum256, 0),
_mm256_extracti128_si256(sum256, 1));
sum64 += _mm_extract_epi64(sum128, 0);
sum64 += _mm_extract_epi64(sum128, 1);
}
buf64 = (const uint64_t *)buf256;
/* Repeat 16-bit one's complement sum (at sum64). */
buf16 = (const uint16_t *)buf64;
while (len >= sizeof(uint16_t)) {
sum64 += *buf16++;
len -= sizeof(uint16_t);
}
/* Add remaining 8 bits to the one's complement sum. */
if (odd)
sum64 += *(const uint8_t *)buf16;
/* Reduce 64-bit unsigned int to 32-bit unsigned int. */
sum64 = (sum64 >> 32) + (sum64 & 0xffffffff);
sum64 += sum64 >> 32;
return (uint32_t)sum64;
}
/**
* csum_unfolded - Calculate the unfolded checksum of a data buffer.
*
* @buf: Input buffer
* @len: Input length
* @init: Initial 32-bit checksum, 0 for no pre-computed checksum
*
* Return: 32-bit unfolded
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint32_t csum_unfolded(const void *buf, size_t len, uint32_t init)
{
intptr_t align = ROUND_UP((intptr_t)buf, sizeof(__m256i));
unsigned int pad = align - (intptr_t)buf;
if (len < pad)
pad = len;
if (pad)
init += sum_16b(buf, pad);
if (len > pad)
init = csum_avx2((void *)align, len - pad, init);
return init;
}
#else /* __AVX2__ */
/**
* csum_unfolded - Calculate the unfolded checksum of a data buffer.
*
* @buf: Input buffer
* @len: Input length
* @init: Initial 32-bit checksum, 0 for no pre-computed checksum
*
* Return: 32-bit unfolded checksum
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint32_t csum_unfolded(const void *buf, size_t len, uint32_t init)
{
return sum_16b(buf, len) + init;
}
#endif /* !__AVX2__ */
/**
* csum() - Compute TCP/IP-style checksum
* @buf: Input buffer
* @len: Input length
* @init: Initial 32-bit checksum, 0 for no pre-computed checksum
*
* Return: 16-bit folded, complemented checksum
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint16_t csum(const void *buf, size_t len, uint32_t init)
{
return (uint16_t)~csum_fold(csum_unfolded(buf, len, init));
}
/**
* csum_iov() - Calculates the unfolded checksum over an array of IO vectors
*
* @iov Pointer to the array of IO vectors
* @n Length of the array
* @init Initial 32-bit checksum, 0 for no pre-computed checksum
*
* Return: 16-bit folded, complemented checksum
*/
/* cppcheck-suppress unusedFunction */
uint16_t csum_iov(const struct iovec *iov, size_t n, uint32_t init)
{
unsigned int i;
for (i = 0; i < n; i++)
init = csum_unfolded(iov[i].iov_base, iov[i].iov_len, init);
return (uint16_t)~csum_fold(init);
}
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