sha1.c

// SPDX-License-Identifier: GPL-2.0
/*
 * SHA1 routine optimized to do word accesses rather than byte accesses,
 * and to avoid unnecessary copies into the context array.
 *
 * This was based on the git SHA1 implementation.
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/bitops.h>
#include <linux/cryptohash.h>
#include <linux/string.h>
#include <asm/unaligned.h>

/*
 * If you have 32 registers or more, the compiler can (and should)
 * try to change the array[] accesses into registers. However, on
 * machines with less than ~25 registers, that won't really work,
 * and at least gcc will make an unholy mess of it.
 *
 * So to avoid that mess which just slows things down, we force
 * the stores to memory to actually happen (we might be better off
 * with a 'W(t)=(val);asm("":"+m" (W(t))' there instead, as
 * suggested by Artur Skawina - that will also make gcc unable to
 * try to do the silly "optimize away loads" part because it won't
 * see what the value will be).
 *
 * Ben Herrenschmidt reports that on PPC, the C version comes close
 * to the optimized asm with this (ie on PPC you don't want that
 * 'volatile', since there are lots of registers).
 *
 * On ARM we get the best code generation by forcing a full memory barrier
 * between each SHA_ROUND, otherwise gcc happily get wild with spilling and
 * the stack frame size simply explode and performance goes down the drain.
 */

#ifdef CONFIG_X86
  #define setW(x, val) (*(volatile __u32 *)&W(x) = (val))
#elif defined(CONFIG_ARM)
  #define setW(x, val) do { W(x) = (val); __asm__("":::"memory"); } while (0)
#else
  #define setW(x, val) (W(x) = (val))
#endif

/* This "rolls" over the 512-bit array */
#define W(x) (array[(x)&15])

/*
 * Where do we get the source from? The first 16 iterations get it from
 * the input data, the next mix it from the 512-bit array.
 */
#define SHA_SRC(t) get_unaligned_be32((__u32 *)data + t)
#define SHA_MIX(t) rol32(W(t+13) ^ W(t+8) ^ W(t+2) ^ W(t), 1)

#define SHA_ROUND(t, input, fn, constant, A, B, C, D, E) do { \
	__u32 TEMP = input(t); setW(t, TEMP); \
	E += TEMP + rol32(A,5) + (fn) + (constant); \
	B = ror32(B, 2); \
	TEMP = E; E = D; D = C; C = B; B = A; A = TEMP; } while (0)

#define T_0_15(t, A, B, C, D, E)  SHA_ROUND(t, SHA_SRC, (((C^D)&B)^D) , 0x5a827999, A, B, C, D, E )
#define T_16_19(t, A, B, C, D, E) SHA_ROUND(t, SHA_MIX, (((C^D)&B)^D) , 0x5a827999, A, B, C, D, E )
#define T_20_39(t, A, B, C, D, E) SHA_ROUND(t, SHA_MIX, (B^C^D) , 0x6ed9eba1, A, B, C, D, E )
#define T_40_59(t, A, B, C, D, E) SHA_ROUND(t, SHA_MIX, ((B&C)+(D&(B^C))) , 0x8f1bbcdc, A, B, C, D, E )
#define T_60_79(t, A, B, C, D, E) SHA_ROUND(t, SHA_MIX, (B^C^D) ,  0xca62c1d6, A, B, C, D, E )

/**
 * sha_transform - single block SHA1 transform
 *
 * @digest: 160 bit digest to update
 * @data:   512 bits of data to hash
 * @array:  16 words of workspace (see note)
 *
 * This function generates a SHA1 digest for a single 512-bit block.
 * Be warned, it does not handle padding and message digest, do not
 * confuse it with the full FIPS 180-1 digest algorithm for variable
 * length messages.
 *
 * Note: If the hash is security sensitive, the caller should be sure
 * to clear the workspace. This is left to the caller to avoid
 * unnecessary clears between chained hashing operations.
 */
void sha_transform(__u32 *digest, const char *data, __u32 *array)
{
	__u32 A, B, C, D, E;
	unsigned int i = 0;

	A = digest[0];
	B = digest[1];
	C = digest[2];
	D = digest[3];
	E = digest[4];

	/* Round 1 - iterations 0-16 take their input from 'data' */
	for (; i < 16; ++i)
		T_0_15(i, A, B, C, D, E);

	/* Round 1 - tail. Input from 512-bit mixing array */
	for (; i < 20; ++i)
		T_16_19(i, A, B, C, D, E);

	/* Round 2 */
	for (; i < 40; ++i)
		T_20_39(i, A, B, C, D, E);

	/* Round 3 */
	for (; i < 60; ++i)
		T_40_59(i, A, B, C, D, E);

	/* Round 4 */
	for (; i < 80; ++i)
		T_60_79(i, A, B, C, D, E);

	digest[0] += A;
	digest[1] += B;
	digest[2] += C;
	digest[3] += D;
	digest[4] += E;
}
EXPORT_SYMBOL(sha_transform);

/**
 * sha_init - initialize the vectors for a SHA1 digest
 * @buf: vector to initialize
 */
void sha_init(__u32 *buf)
{
	buf[0] = 0x67452301;
	buf[1] = 0xefcdab89;
	buf[2] = 0x98badcfe;
	buf[3] = 0x10325476;
	buf[4] = 0xc3d2e1f0;
}
EXPORT_SYMBOL(sha_init);