admin/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2025-12-07 11:56:58 +00:00
Code Issues Packages Projects Releases Wiki Activity

lib/base64: rework encode/decode for speed and stricter validation

Browse Source 
The old base64 implementation relied on a bit-accumulator loop, which was
slow for larger inputs and too permissive in validation.  It would accept
extra '=', missing '=', or even '=' appearing in the middle of the input,
allowing malformed strings to pass.  This patch reworks the internals to
improve performance and enforce stricter validation.

Changes:
 - Encoder:
   * Process input in 3-byte blocks, mapping 24 bits into four 6-bit
     symbols, avoiding bit-by-bit shifting and reducing loop iterations.
   * Handle the final 1-2 leftover bytes explicitly and emit '=' only when
     requested.
 - Decoder:
   * Based on the reverse lookup tables from the previous patch, decode
     input in 4-character groups.
   * Each group is looked up directly, converted into numeric values, and
     combined into 3 output bytes.
   * Explicitly handle padded and unpadded forms:
      - With padding: input length must be a multiple of 4, and '=' is
        allowed only in the last two positions. Reject stray or early '='.
      - Without padding: validate tail lengths (2 or 3 chars) and require
        unused low bits to be zero.
   * Removed the bit-accumulator style loop to reduce loop iterations.

Performance (x86_64, Intel Core i7-10700 @ 2.90GHz, avg over 1000 runs,
KUnit):

Encode:
  64B   ~90ns   -> ~32ns   (~2.8x)
  1KB  ~1332ns  -> ~510ns  (~2.6x)

Decode:
  64B  ~1530ns  -> ~35ns   (~43.7x)
  1KB ~27726ns  -> ~530ns  (~52.3x)

[akpm@linux-foundation.org: remove u32 casts, per David and Guan-Chun]
Link: https://lkml.kernel.org/r/20251114060132.89279-1-409411716@gms.tku.edu.tw
Co-developed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Co-developed-by: Yu-Sheng Huang <home7438072@gmail.com>
Signed-off-by: Yu-Sheng Huang <home7438072@gmail.com>
Signed-off-by: Guan-Chun Wu <409411716@gms.tku.edu.tw>
Reviewed-by: David Laight <david.laight.linux@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Cc: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Guan-Chun Wu
2025-11-14 14:01:32 +08:00
committed by Andrew Morton
parent c4eb7ad32e
commit 9c7d3cf94d
1 changed files with 68 additions and 41 deletions
Download Patch File Download Diff File Expand all files Collapse all files

109
lib/base64.c
View File

@@ -80,28 +80,38 @@ static const s8 base64_rev_maps[][256] = {
int base64_encode(const u8 *src, int srclen, char *dst, bool padding, enum base64_variant variant)
{
u32 ac = 0;
int bits = 0;
int i;
char *cp = dst;
const char *base64_table = base64_tables[variant];
for (i = 0; i < srclen; i++) {
ac = (ac << 8) | src[i];
bits += 8;
do {
bits -= 6;
*cp++ = base64_table[(ac >> bits) & 0x3f];
} while (bits >= 6);
while (srclen >= 3) {
ac = src[0] << 16 | src[1] << 8 | src[2];
*cp++ = base64_table[ac >> 18];
*cp++ = base64_table[(ac >> 12) & 0x3f];
*cp++ = base64_table[(ac >> 6) & 0x3f];
*cp++ = base64_table[ac & 0x3f];
src += 3;
srclen -= 3;
}
if (bits) {
*cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
bits -= 6;
}
if (padding) {
while (bits < 0) {
switch (srclen) {
case 2:
ac = src[0] << 16 | src[1] << 8;
*cp++ = base64_table[ac >> 18];
*cp++ = base64_table[(ac >> 12) & 0x3f];
*cp++ = base64_table[(ac >> 6) & 0x3f];
if (padding)
*cp++ = '=';
break;
case 1:
ac = src[0] << 16;
*cp++ = base64_table[ac >> 18];
*cp++ = base64_table[(ac >> 12) & 0x3f];
if (padding) {
*cp++ = '=';
*cp++ = '=';
bits += 2;
}
break;
}
return cp - dst;
}
@@ -117,41 +127,58 @@ EXPORT_SYMBOL_GPL(base64_encode);
*
* Decodes a string using the selected Base64 variant.
*
* This implementation hasn't been optimized for performance.
*
* Return: the length of the resulting decoded binary data in bytes,
* or -1 if the string isn't a valid Base64 string.
*/
int base64_decode(const char *src, int srclen, u8 *dst, bool padding, enum base64_variant variant)
{
u32 ac = 0;
int bits = 0;
int i;
u8 *bp = dst;
s8 ch;
s8 input[4];
s32 val;
const u8 *s = (const u8 *)src;
const s8 *base64_rev_tables = base64_rev_maps[variant];
for (i = 0; i < srclen; i++) {
if (padding) {
if (src[i] == '=') {
ac = (ac << 6);
bits += 6;
if (bits >= 8)
bits -= 8;
continue;
}
}
ch = base64_rev_maps[variant][(u8)src[i]];
if (ch == -1)
return -1;
ac = (ac << 6) | ch;
bits += 6;
if (bits >= 8) {
bits -= 8;
*bp++ = (u8)(ac >> bits);
while (srclen >= 4) {
input[0] = base64_rev_tables[s[0]];
input[1] = base64_rev_tables[s[1]];
input[2] = base64_rev_tables[s[2]];
input[3] = base64_rev_tables[s[3]];
val = input[0] << 18 | input[1] << 12 | input[2] << 6 | input[3];
if (unlikely(val < 0)) {
if (!padding || srclen != 4 || s[3] != '=')
return -1;
padding = 0;
srclen = s[2] == '=' ? 2 : 3;
break;
}
*bp++ = val >> 16;
*bp++ = val >> 8;
*bp++ = val;
s += 4;
srclen -= 4;
}
if (ac & ((1 << bits) - 1))
if (likely(!srclen))
return bp - dst;
if (padding || srclen == 1)
return -1;
val = (base64_rev_tables[s[0]] << 12) | (base64_rev_tables[s[1]] << 6);
*bp++ = val >> 10;
if (srclen == 2) {
if (val & 0x800003ff)
return -1;
} else {
val |= base64_rev_tables[s[2]];
if (val & 0x80000003)
return -1;
*bp++ = val >> 2;
}
return bp - dst;
}
EXPORT_SYMBOL_GPL(base64_decode);