cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
Log | Files | Refs | README | LICENSE | sfeed.txt

ts_kmp.c (4220B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/*
      3 * lib/ts_kmp.c		Knuth-Morris-Pratt text search implementation
      4 *
      5 * Authors:	Thomas Graf <tgraf@suug.ch>
      6 *
      7 * ==========================================================================
      8 * 
      9 *   Implements a linear-time string-matching algorithm due to Knuth,
     10 *   Morris, and Pratt [1]. Their algorithm avoids the explicit
     11 *   computation of the transition function DELTA altogether. Its
     12 *   matching time is O(n), for n being length(text), using just an
     13 *   auxiliary function PI[1..m], for m being length(pattern),
     14 *   precomputed from the pattern in time O(m). The array PI allows
     15 *   the transition function DELTA to be computed efficiently
     16 *   "on the fly" as needed. Roughly speaking, for any state
     17 *   "q" = 0,1,...,m and any character "a" in SIGMA, the value
     18 *   PI["q"] contains the information that is independent of "a" and
     19 *   is needed to compute DELTA("q", "a") [2]. Since the array PI
     20 *   has only m entries, whereas DELTA has O(m|SIGMA|) entries, we
     21 *   save a factor of |SIGMA| in the preprocessing time by computing
     22 *   PI rather than DELTA.
     23 *
     24 *   [1] Cormen, Leiserson, Rivest, Stein
     25 *       Introdcution to Algorithms, 2nd Edition, MIT Press
     26 *   [2] See finite automaton theory
     27 */
     28
     29#include <linux/module.h>
     30#include <linux/types.h>
     31#include <linux/string.h>
     32#include <linux/ctype.h>
     33#include <linux/textsearch.h>
     34
     35struct ts_kmp
     36{
     37	u8 *		pattern;
     38	unsigned int	pattern_len;
     39	unsigned int	prefix_tbl[];
     40};
     41
     42static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state)
     43{
     44	struct ts_kmp *kmp = ts_config_priv(conf);
     45	unsigned int i, q = 0, text_len, consumed = state->offset;
     46	const u8 *text;
     47	const int icase = conf->flags & TS_IGNORECASE;
     48
     49	for (;;) {
     50		text_len = conf->get_next_block(consumed, &text, conf, state);
     51
     52		if (unlikely(text_len == 0))
     53			break;
     54
     55		for (i = 0; i < text_len; i++) {
     56			while (q > 0 && kmp->pattern[q]
     57			    != (icase ? toupper(text[i]) : text[i]))
     58				q = kmp->prefix_tbl[q - 1];
     59			if (kmp->pattern[q]
     60			    == (icase ? toupper(text[i]) : text[i]))
     61				q++;
     62			if (unlikely(q == kmp->pattern_len)) {
     63				state->offset = consumed + i + 1;
     64				return state->offset - kmp->pattern_len;
     65			}
     66		}
     67
     68		consumed += text_len;
     69	}
     70
     71	return UINT_MAX;
     72}
     73
     74static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len,
     75				      unsigned int *prefix_tbl, int flags)
     76{
     77	unsigned int k, q;
     78	const u8 icase = flags & TS_IGNORECASE;
     79
     80	for (k = 0, q = 1; q < len; q++) {
     81		while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k])
     82		    != (icase ? toupper(pattern[q]) : pattern[q]))
     83			k = prefix_tbl[k-1];
     84		if ((icase ? toupper(pattern[k]) : pattern[k])
     85		    == (icase ? toupper(pattern[q]) : pattern[q]))
     86			k++;
     87		prefix_tbl[q] = k;
     88	}
     89}
     90
     91static struct ts_config *kmp_init(const void *pattern, unsigned int len,
     92				  gfp_t gfp_mask, int flags)
     93{
     94	struct ts_config *conf;
     95	struct ts_kmp *kmp;
     96	int i;
     97	unsigned int prefix_tbl_len = len * sizeof(unsigned int);
     98	size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
     99
    100	conf = alloc_ts_config(priv_size, gfp_mask);
    101	if (IS_ERR(conf))
    102		return conf;
    103
    104	conf->flags = flags;
    105	kmp = ts_config_priv(conf);
    106	kmp->pattern_len = len;
    107	compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags);
    108	kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len;
    109	if (flags & TS_IGNORECASE)
    110		for (i = 0; i < len; i++)
    111			kmp->pattern[i] = toupper(((u8 *)pattern)[i]);
    112	else
    113		memcpy(kmp->pattern, pattern, len);
    114
    115	return conf;
    116}
    117
    118static void *kmp_get_pattern(struct ts_config *conf)
    119{
    120	struct ts_kmp *kmp = ts_config_priv(conf);
    121	return kmp->pattern;
    122}
    123
    124static unsigned int kmp_get_pattern_len(struct ts_config *conf)
    125{
    126	struct ts_kmp *kmp = ts_config_priv(conf);
    127	return kmp->pattern_len;
    128}
    129
    130static struct ts_ops kmp_ops = {
    131	.name		  = "kmp",
    132	.find		  = kmp_find,
    133	.init		  = kmp_init,
    134	.get_pattern	  = kmp_get_pattern,
    135	.get_pattern_len  = kmp_get_pattern_len,
    136	.owner		  = THIS_MODULE,
    137	.list		  = LIST_HEAD_INIT(kmp_ops.list)
    138};
    139
    140static int __init init_kmp(void)
    141{
    142	return textsearch_register(&kmp_ops);
    143}
    144
    145static void __exit exit_kmp(void)
    146{
    147	textsearch_unregister(&kmp_ops);
    148}
    149
    150MODULE_LICENSE("GPL");
    151
    152module_init(init_kmp);
    153module_exit(exit_kmp);