cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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key.c (3529B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/* Key to pathname encoder
      3 *
      4 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
      5 * Written by David Howells (dhowells@redhat.com)
      6 */
      7
      8#include <linux/slab.h>
      9#include "internal.h"
     10
     11static const char cachefiles_charmap[64] =
     12	"0123456789"			/* 0 - 9 */
     13	"abcdefghijklmnopqrstuvwxyz"	/* 10 - 35 */
     14	"ABCDEFGHIJKLMNOPQRSTUVWXYZ"	/* 36 - 61 */
     15	"_-"				/* 62 - 63 */
     16	;
     17
     18static const char cachefiles_filecharmap[256] = {
     19	/* we skip space and tab and control chars */
     20	[33 ... 46] = 1,		/* '!' -> '.' */
     21	/* we skip '/' as it's significant to pathwalk */
     22	[48 ... 127] = 1,		/* '0' -> '~' */
     23};
     24
     25static inline unsigned int how_many_hex_digits(unsigned int x)
     26{
     27	return x ? round_up(ilog2(x) + 1, 4) / 4 : 0;
     28}
     29
     30/*
     31 * turn the raw key into something cooked
     32 * - the key may be up to NAME_MAX in length (including the length word)
     33 *   - "base64" encode the strange keys, mapping 3 bytes of raw to four of
     34 *     cooked
     35 *   - need to cut the cooked key into 252 char lengths (189 raw bytes)
     36 */
     37bool cachefiles_cook_key(struct cachefiles_object *object)
     38{
     39	const u8 *key = fscache_get_key(object->cookie), *kend;
     40	unsigned char ch;
     41	unsigned int acc, i, n, nle, nbe, keylen = object->cookie->key_len;
     42	unsigned int b64len, len, print, pad;
     43	char *name, sep;
     44
     45	_enter(",%u,%*phN", keylen, keylen, key);
     46
     47	BUG_ON(keylen > NAME_MAX - 3);
     48
     49	print = 1;
     50	for (i = 0; i < keylen; i++) {
     51		ch = key[i];
     52		print &= cachefiles_filecharmap[ch];
     53	}
     54
     55	/* If the path is usable ASCII, then we render it directly */
     56	if (print) {
     57		len = 1 + keylen;
     58		name = kmalloc(len + 1, GFP_KERNEL);
     59		if (!name)
     60			return false;
     61
     62		name[0] = 'D'; /* Data object type, string encoding */
     63		memcpy(name + 1, key, keylen);
     64		goto success;
     65	}
     66
     67	/* See if it makes sense to encode it as "hex,hex,hex" for each 32-bit
     68	 * chunk.  We rely on the key having been padded out to a whole number
     69	 * of 32-bit words.
     70	 */
     71	n = round_up(keylen, 4);
     72	nbe = nle = 0;
     73	for (i = 0; i < n; i += 4) {
     74		u32 be = be32_to_cpu(*(__be32 *)(key + i));
     75		u32 le = le32_to_cpu(*(__le32 *)(key + i));
     76
     77		nbe += 1 + how_many_hex_digits(be);
     78		nle += 1 + how_many_hex_digits(le);
     79	}
     80
     81	b64len = DIV_ROUND_UP(keylen, 3);
     82	pad = b64len * 3 - keylen;
     83	b64len = 2 + b64len * 4; /* Length if we base64-encode it */
     84	_debug("len=%u nbe=%u nle=%u b64=%u", keylen, nbe, nle, b64len);
     85	if (nbe < b64len || nle < b64len) {
     86		unsigned int nlen = min(nbe, nle) + 1;
     87		name = kmalloc(nlen, GFP_KERNEL);
     88		if (!name)
     89			return false;
     90		sep = (nbe <= nle) ? 'S' : 'T'; /* Encoding indicator */
     91		len = 0;
     92		for (i = 0; i < n; i += 4) {
     93			u32 x;
     94			if (nbe <= nle)
     95				x = be32_to_cpu(*(__be32 *)(key + i));
     96			else
     97				x = le32_to_cpu(*(__le32 *)(key + i));
     98			name[len++] = sep;
     99			if (x != 0)
    100				len += snprintf(name + len, nlen - len, "%x", x);
    101			sep = ',';
    102		}
    103		goto success;
    104	}
    105
    106	/* We need to base64-encode it */
    107	name = kmalloc(b64len + 1, GFP_KERNEL);
    108	if (!name)
    109		return false;
    110
    111	name[0] = 'E';
    112	name[1] = '0' + pad;
    113	len = 2;
    114	kend = key + keylen;
    115	do {
    116		acc  = *key++;
    117		if (key < kend) {
    118			acc |= *key++ << 8;
    119			if (key < kend)
    120				acc |= *key++ << 16;
    121		}
    122
    123		name[len++] = cachefiles_charmap[acc & 63];
    124		acc >>= 6;
    125		name[len++] = cachefiles_charmap[acc & 63];
    126		acc >>= 6;
    127		name[len++] = cachefiles_charmap[acc & 63];
    128		acc >>= 6;
    129		name[len++] = cachefiles_charmap[acc & 63];
    130	} while (key < kend);
    131
    132success:
    133	name[len] = 0;
    134	object->d_name = name;
    135	object->d_name_len = len;
    136	_leave(" = %s", object->d_name);
    137	return true;
    138}