1// SPDX-License-Identifier: GPL-2.0-only
  2// Copyright (C) 2019-2020 Arm Ltd.
  3
  4#include <linux/compiler.h>
  5#include <linux/kasan-checks.h>
  6#include <linux/kernel.h>
  7
  8#include <net/checksum.h>
  9
 10/* Looks dumb, but generates nice-ish code */
 11static u64 accumulate(u64 sum, u64 data)
 12{
 13	__uint128_t tmp = (__uint128_t)sum + data;
 14	return tmp + (tmp >> 64);
 15}
 16
 17/*
 18 * We over-read the buffer and this makes KASAN unhappy. Instead, disable
 19 * instrumentation and call kasan explicitly.
 20 */
 21unsigned int __no_sanitize_address do_csum(const unsigned char *buff, int len)
 22{
 23	unsigned int offset, shift, sum;
 24	const u64 *ptr;
 25	u64 data, sum64 = 0;
 26
 27	if (unlikely(len == 0))
 28		return 0;
 29
 30	offset = (unsigned long)buff & 7;
 31	/*
 32	 * This is to all intents and purposes safe, since rounding down cannot
 33	 * result in a different page or cache line being accessed, and @buff
 34	 * should absolutely not be pointing to anything read-sensitive. We do,
 35	 * however, have to be careful not to piss off KASAN, which means using
 36	 * unchecked reads to accommodate the head and tail, for which we'll
 37	 * compensate with an explicit check up-front.
 38	 */
 39	kasan_check_read(buff, len);
 40	ptr = (u64 *)(buff - offset);
 41	len = len + offset - 8;
 42
 43	/*
 44	 * Head: zero out any excess leading bytes. Shifting back by the same
 45	 * amount should be at least as fast as any other way of handling the
 46	 * odd/even alignment, and means we can ignore it until the very end.
 47	 */
 48	shift = offset * 8;
 49	data = *ptr++;
 50#ifdef __LITTLE_ENDIAN
 51	data = (data >> shift) << shift;
 52#else
 53	data = (data << shift) >> shift;
 54#endif
 55
 56	/*
 57	 * Body: straightforward aligned loads from here on (the paired loads
 58	 * underlying the quadword type still only need dword alignment). The
 59	 * main loop strictly excludes the tail, so the second loop will always
 60	 * run at least once.
 61	 */
 62	while (unlikely(len > 64)) {
 63		__uint128_t tmp1, tmp2, tmp3, tmp4;
 64
 65		tmp1 = *(__uint128_t *)ptr;
 66		tmp2 = *(__uint128_t *)(ptr + 2);
 67		tmp3 = *(__uint128_t *)(ptr + 4);
 68		tmp4 = *(__uint128_t *)(ptr + 6);
 69
 70		len -= 64;
 71		ptr += 8;
 72
 73		/* This is the "don't dump the carry flag into a GPR" idiom */
 74		tmp1 += (tmp1 >> 64) | (tmp1 << 64);
 75		tmp2 += (tmp2 >> 64) | (tmp2 << 64);
 76		tmp3 += (tmp3 >> 64) | (tmp3 << 64);
 77		tmp4 += (tmp4 >> 64) | (tmp4 << 64);
 78		tmp1 = ((tmp1 >> 64) << 64) | (tmp2 >> 64);
 79		tmp1 += (tmp1 >> 64) | (tmp1 << 64);
 80		tmp3 = ((tmp3 >> 64) << 64) | (tmp4 >> 64);
 81		tmp3 += (tmp3 >> 64) | (tmp3 << 64);
 82		tmp1 = ((tmp1 >> 64) << 64) | (tmp3 >> 64);
 83		tmp1 += (tmp1 >> 64) | (tmp1 << 64);
 84		tmp1 = ((tmp1 >> 64) << 64) | sum64;
 85		tmp1 += (tmp1 >> 64) | (tmp1 << 64);
 86		sum64 = tmp1 >> 64;
 87	}
 88	while (len > 8) {
 89		__uint128_t tmp;
 90
 91		sum64 = accumulate(sum64, data);
 92		tmp = *(__uint128_t *)ptr;
 93
 94		len -= 16;
 95		ptr += 2;
 96
 97#ifdef __LITTLE_ENDIAN
 98		data = tmp >> 64;
 99		sum64 = accumulate(sum64, tmp);
100#else
101		data = tmp;
102		sum64 = accumulate(sum64, tmp >> 64);
103#endif
104	}
105	if (len > 0) {
106		sum64 = accumulate(sum64, data);
107		data = *ptr;
108		len -= 8;
109	}
110	/*
111	 * Tail: zero any over-read bytes similarly to the head, again
112	 * preserving odd/even alignment.
113	 */
114	shift = len * -8;
115#ifdef __LITTLE_ENDIAN
116	data = (data << shift) >> shift;
117#else
118	data = (data >> shift) << shift;
119#endif
120	sum64 = accumulate(sum64, data);
121
122	/* Finally, folding */
123	sum64 += (sum64 >> 32) | (sum64 << 32);
124	sum = sum64 >> 32;
125	sum += (sum >> 16) | (sum << 16);
126	if (offset & 1)
127		return (u16)swab32(sum);
128
129	return sum >> 16;
130}
131
132__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
133			const struct in6_addr *daddr,
134			__u32 len, __u8 proto, __wsum csum)
135{
136	__uint128_t src, dst;
137	u64 sum = (__force u64)csum;
138
139	src = *(const __uint128_t *)saddr->s6_addr;
140	dst = *(const __uint128_t *)daddr->s6_addr;
141
142	sum += (__force u32)htonl(len);
143#ifdef __LITTLE_ENDIAN
144	sum += (u32)proto << 24;
145#else
146	sum += proto;
147#endif
148	src += (src >> 64) | (src << 64);
149	dst += (dst >> 64) | (dst << 64);
150
151	sum = accumulate(sum, src >> 64);
152	sum = accumulate(sum, dst >> 64);
153
154	sum += ((sum >> 32) | (sum << 32));
155	return csum_fold((__force __wsum)(sum >> 32));
156}
157EXPORT_SYMBOL(csum_ipv6_magic);