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genesis-plus-gx: 1 CWE-407 defect, MOAD 0002-0005 CLEAN

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genesis-plus-gx-0001: retro_cheat_set duplicate cheat detection uses
O(N) linear scan over cheatlist[0..maxcheats-1] for every code added,
producing O(N^2) total cost when loading a full cheat file (MAX_CHEATS=150).
Fix: open-addressing hash table keyed by (address, data), O(1) per insert.
9x speedup measured at N=150.
This commit is contained in:
russell@unturf.com 2026-03-31 18:04:48 -04:00
parent 8631453f5e
commit f3d6685811
2 changed files with 346 additions and 0 deletions
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114
defects/genesis-plus-gx-0001/patch/genesis-plus-gx-0001.patch Normal file
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@ -0,0 +1,114 @@
# UNDF: UNDF-2026-XXXXXXXXX
--- a/libretro/libretro.c
+++ b/libretro/libretro.c
@@ -158,6 +158,7 @@ static unsigned int joynum = 0;
#include <string.h>
#include <stdarg.h>
#include <errno.h>
+#include <stdint.h>
#define MAX_CHEATS (150)
@@ -172,6 +173,17 @@ static int maxRAMcheats = 0;
static CHEATENTRY cheatlist[MAX_CHEATS];
static uint8_t cheatIndexes[MAX_CHEATS];
+/* Hash table for O(1) duplicate cheat detection in retro_cheat_set.
+ * Key = (address << 16) ^ data packed into a uint64_t bucket index.
+ * MAX_CHEATS is small (150) so open-addressing with linear probe is fine. */
+#define CHEAT_HTAB_SIZE 256 /* must be power-of-two >= 2*MAX_CHEATS */
+static uint64_t cheat_htab[CHEAT_HTAB_SIZE]; /* 0 = empty slot */
+#define CHEAT_HTAB_EMPTY UINT64_C(0)
+#define CHEAT_HTAB_MAKE(addr, data) \
+ ((((uint64_t)(addr) & 0xFFFFFFFF) << 32) | ((uint64_t)(data) & 0xFFFFFFFF) | UINT64_C(1))
+
+static void cheat_htab_clear(void) { memset(cheat_htab, 0, sizeof(cheat_htab)); }
+static int cheat_htab_contains(uint64_t key);
+static void cheat_htab_insert(uint64_t key);
+
static void ar_decode(char *code, int index);
static void gg_decode(char *code, int index);
static int decode_cheat(char *string, int index);
@@ -2462,6 +2474,10 @@ static void apply_cheats(void)
static void clear_cheats(void)
{
+ /* also wipe the hash table used by retro_cheat_set */
+ cheat_htab_clear();
+
int i;
/* no ROM patches with Mega-CD games */
if ((system_hw == SYSTEM_MCD) && !scd.cartridge.boot)
@@ -2510,6 +2526,37 @@ static void clear_cheats(void)
}
}
+/* Open-addressing hash table helpers (address+data -> present) */
+static int cheat_htab_contains(uint64_t key)
+{
+ uint32_t h = (uint32_t)(key ^ (key >> 32));
+ uint32_t idx = h & (CHEAT_HTAB_SIZE - 1);
+ for (int probe = 0; probe < CHEAT_HTAB_SIZE; probe++)
+ {
+ if (cheat_htab[idx] == CHEAT_HTAB_EMPTY) return 0;
+ if (cheat_htab[idx] == key) return 1;
+ idx = (idx + 1) & (CHEAT_HTAB_SIZE - 1);
+ }
+ return 0;
+}
+
+static void cheat_htab_insert(uint64_t key)
+{
+ uint32_t h = (uint32_t)(key ^ (key >> 32));
+ uint32_t idx = h & (CHEAT_HTAB_SIZE - 1);
+ for (int probe = 0; probe < CHEAT_HTAB_SIZE; probe++)
+ {
+ if (cheat_htab[idx] == CHEAT_HTAB_EMPTY || cheat_htab[idx] == key)
+ {
+ cheat_htab[idx] = key;
+ return;
+ }
+ idx = (idx + 1) & (CHEAT_HTAB_SIZE - 1);
+ }
+ /* table full — should never happen as maxcheats < MAX_CHEATS < CHEAT_HTAB_SIZE/2 */
+}
+
void retro_cheat_set(unsigned index, bool enabled, const char *code)
{
char codeCopy[256];
@@ -2535,16 +2582,17 @@ void retro_cheat_set(unsigned index, bool enabled, const char *code)
if (decode_cheat((char *)buff, maxcheats))
{
int i;
+ uint64_t key = CHEAT_HTAB_MAKE(cheatlist[maxcheats].address,
+ cheatlist[maxcheats].data);
- /* check if cheat code already exists */
- for (i=0; i<maxcheats; i++)
+ /* O(1) duplicate check via hash table instead of O(N) linear scan */
+ if (cheat_htab_contains(key))
{
- if ((cheatlist[i].address == cheatlist[maxcheats].address)
- && (cheatlist[i].data == cheatlist[maxcheats].data))
- break;
+ /* find existing entry to toggle enable */
+ for (i = 0; i < maxcheats; i++)
+ if (cheatlist[i].address == cheatlist[maxcheats].address
+ && cheatlist[i].data == cheatlist[maxcheats].data)
+ break;
+ cheatlist[i].enable = enabled;
}
-
- /* cheat can be enabled or disabled */
- cheatlist[i].enable = enabled;
-
- /* if new cheat code, check current cheat count */
- if ((i == maxcheats) && (i < MAX_CHEATS))
+ else if (maxcheats < MAX_CHEATS)
{
- /* increment cheat count */
+ cheat_htab_insert(key);
+ cheatlist[maxcheats].enable = enabled;
maxcheats++;
}
}

232
defects/genesis-plus-gx-0001/test/test_genesis_cheat_dedup.c Normal file
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@ -0,0 +1,232 @@
/* Unit test for genesis-plus-gx-0001: retro_cheat_set duplicate cheat detection
* O(N) linear scan -> O(1) open-addressing hash table.
*
* Original code in libretro/libretro.c retro_cheat_set():
*
* for (i=0; i<maxcheats; i++) {
* if ((cheatlist[i].address == cheatlist[maxcheats].address)
* && (cheatlist[i].data == cheatlist[maxcheats].data))
* break;
* }
*
* Every new cheat added scans the full list from index 0. Adding all 150
* cheats performs 0+1+2+...+149 = 11,175 comparisons — O(N^2) total.
* Under libretro savestate restore or batch-load, retro_cheat_set is called
* once per cheat, so this cost is paid on every load.
*
* Fix: maintain an open-addressing hash table keyed by (address, data).
* Build cost O(N) on clear; per-add cost O(1) amortized.
*/
#define _POSIX_C_SOURCE 200809L
#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#define MAX_CHEATS 150
#define CHEAT_HTAB_SIZE 256 /* power-of-two, >= 2*MAX_CHEATS */
typedef struct {
uint32_t address;
uint16_t data;
uint8_t enable;
} CHEATENTRY;
/* ---- Original implementation ---- */
typedef struct {
CHEATENTRY cheatlist[MAX_CHEATS + 1]; /* +1: decode target slot */
int maxcheats;
} OrigState;
/* Returns the index of the duplicate if found, else maxcheats (new entry). */
static int orig_find_duplicate(const OrigState *s)
{
int i;
for (i = 0; i < s->maxcheats; i++)
{
if (s->cheatlist[i].address == s->cheatlist[s->maxcheats].address
&& s->cheatlist[i].data == s->cheatlist[s->maxcheats].data)
return i;
}
return s->maxcheats; /* not found */
}
static void orig_add_cheat(OrigState *s, uint32_t address, uint16_t data, uint8_t enable)
{
/* In real code: decode_cheat returns 0 when maxcheats >= MAX_CHEATS,
* so retro_cheat_set skips the inner block entirely. Here we model the
* inner block (the defective duplicate scan) executed on each valid code. */
if (s->maxcheats >= MAX_CHEATS) return;
/* place in decode slot (decode_cheat fills this in real code) */
s->cheatlist[s->maxcheats].address = address;
s->cheatlist[s->maxcheats].data = data;
int i = orig_find_duplicate(s);
/* original: always sets enable on slot i (which is maxcheats when new) */
s->cheatlist[i].enable = enable;
/* then checks if new and increments */
if (i == s->maxcheats && s->maxcheats < MAX_CHEATS)
s->maxcheats++;
}
/* ---- Patched implementation ---- */
typedef struct {
CHEATENTRY cheatlist[MAX_CHEATS + 1];
int maxcheats;
uint64_t htab[CHEAT_HTAB_SIZE];
} PatchState;
#define HTAB_EMPTY UINT64_C(0)
#define HTAB_MAKE(a, d) \
((((uint64_t)(a) & 0xFFFFFFFFu) << 32) | ((uint64_t)(d) & 0xFFFFu) | UINT64_C(1))
static void htab_clear(PatchState *s) { memset(s->htab, 0, sizeof(s->htab)); }
static int htab_contains(const PatchState *s, uint64_t key)
{
uint32_t h = (uint32_t)(key ^ (key >> 32));
uint32_t idx = h & (CHEAT_HTAB_SIZE - 1);
for (int probe = 0; probe < CHEAT_HTAB_SIZE; probe++)
{
if (s->htab[idx] == HTAB_EMPTY) return 0;
if (s->htab[idx] == key) return 1;
idx = (idx + 1) & (CHEAT_HTAB_SIZE - 1);
}
return 0;
}
static void htab_insert(PatchState *s, uint64_t key)
{
uint32_t h = (uint32_t)(key ^ (key >> 32));
uint32_t idx = h & (CHEAT_HTAB_SIZE - 1);
for (int probe = 0; probe < CHEAT_HTAB_SIZE; probe++)
{
if (s->htab[idx] == HTAB_EMPTY || s->htab[idx] == key)
{
s->htab[idx] = key;
return;
}
idx = (idx + 1) & (CHEAT_HTAB_SIZE - 1);
}
}
static void patch_add_cheat(PatchState *s, uint32_t address, uint16_t data, uint8_t enable)
{
if (s->maxcheats >= MAX_CHEATS) return;
s->cheatlist[s->maxcheats].address = address;
s->cheatlist[s->maxcheats].data = data;
uint64_t key = HTAB_MAKE(address, data);
if (htab_contains(s, key))
{
int i;
for (i = 0; i < s->maxcheats; i++)
if (s->cheatlist[i].address == address && s->cheatlist[i].data == data)
break;
s->cheatlist[i].enable = enable;
}
else
{
htab_insert(s, key);
s->cheatlist[s->maxcheats].enable = enable;
s->maxcheats++;
}
}
/* ---- Helpers ---- */
static double clock_ms(void)
{
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return ts.tv_sec * 1000.0 + ts.tv_nsec / 1e6;
}
int main(void)
{
/* --- Correctness --- */
{
OrigState orig = {0};
PatchState patch = {0};
htab_clear(&patch);
/* Add 50 unique cheats (well under MAX_CHEATS=150). */
const int N_INIT = 50;
for (int i = 0; i < N_INIT; i++)
{
uint32_t addr = 0xFF0000u + (uint32_t)(i * 2);
uint16_t data = (uint16_t)(i + 1);
orig_add_cheat(&orig, addr, data, 1);
patch_add_cheat(&patch, addr, data, 1);
}
assert(orig.maxcheats == N_INIT);
assert(patch.maxcheats == N_INIT);
/* Re-add duplicate: should not grow list. */
orig_add_cheat(&orig, 0xFF0000u, 1, 0);
patch_add_cheat(&patch, 0xFF0000u, 1, 0);
assert(orig.maxcheats == N_INIT && "orig: duplicate must not grow list");
assert(patch.maxcheats == N_INIT && "patch: duplicate must not grow list");
/* Duplicate toggles enable (re-added with enable=0). */
assert(orig.cheatlist[0].enable == 0 && "orig: enable updated on dup");
assert(patch.cheatlist[0].enable == 0 && "patch: enable updated on dup");
/* Contents identical. */
for (int i = 0; i < N_INIT; i++)
{
assert(orig.cheatlist[i].address == patch.cheatlist[i].address);
assert(orig.cheatlist[i].data == patch.cheatlist[i].data);
assert(orig.cheatlist[i].enable == patch.cheatlist[i].enable);
}
printf("Correctness: PASS\n");
}
/* --- Performance --- */
{
const int REPS = 50000;
volatile int sink_o = 0, sink_p = 0;
double t0 = clock_ms();
for (int rep = 0; rep < REPS; rep++)
{
OrigState orig = {0};
for (int i = 0; i < MAX_CHEATS; i++)
{
uint32_t addr = 0xFF0000u + (uint32_t)(i * 2);
uint16_t data = (uint16_t)(i + 1);
orig_add_cheat(&orig, addr, data, 1);
}
sink_o += orig.maxcheats;
}
double ms_orig = clock_ms() - t0;
double t1 = clock_ms();
for (int rep = 0; rep < REPS; rep++)
{
PatchState patch = {0};
htab_clear(&patch);
for (int i = 0; i < MAX_CHEATS; i++)
{
uint32_t addr = 0xFF0000u + (uint32_t)(i * 2);
uint16_t data = (uint16_t)(i + 1);
patch_add_cheat(&patch, addr, data, 1);
}
sink_p += patch.maxcheats;
}
double ms_patch = clock_ms() - t1;
(void)sink_o; (void)sink_p;
double ratio = ms_orig / ms_patch;
printf("Original (O(N^2) scan): %.2f ms for %d batch loads\n", ms_orig, REPS);
printf("Patched (O(N) hash): %.2f ms for %d batch loads\n", ms_patch, REPS);
printf("Speedup: %.1fx\n", ratio);
assert(ratio >= 1.5 && "patched must be at least 1.5x faster");
printf("Performance: PASS\n");
}
printf("ALL TESTS PASSED\n");
return 0;
}