drivers/misc/lkdtm/bugs.c - linux/torvalds/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * This is for all the tests related to logic bugs (e.g. bad dereferences,
  * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
  * lockups) along with other things that don't fit well into existing LKDTM
  * test source files.
  */
 #include "lkdtm.h"
 #include <linux/list.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/task_stack.h>
 #include <linux/uaccess.h>

 struct lkdtm_list {
 	struct list_head node;
 };

 /*
  * Make sure our attempts to over run the kernel stack doesn't trigger
  * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
  * recurse past the end of THREAD_SIZE by default.
  */
 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
 #else
 #define REC_STACK_SIZE (THREAD_SIZE / 8)
 #endif
 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)

 static int recur_count = REC_NUM_DEFAULT;

 static DEFINE_SPINLOCK(lock_me_up);

 /*
  * Make sure compiler does not optimize this function or stack frame away:
  * - function marked noinline
  * - stack variables are marked volatile
  * - stack variables are written (memset()) and read (pr_info())
  * - function has external effects (pr_info())
  * */
 static int noinline recursive_loop(int remaining)
 {
 	volatile char buf[REC_STACK_SIZE];

 	memset((void *)buf, remaining & 0xFF, sizeof(buf));
 	pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
 		recur_count);
 	if (!remaining)
 		return 0;
 	else
 		return recursive_loop(remaining - 1);
 }

 /* If the depth is negative, use the default, otherwise keep parameter. */
 void __init lkdtm_bugs_init(int *recur_param)
 {
 	if (*recur_param < 0)
 		*recur_param = recur_count;
 	else
 		recur_count = *recur_param;
 }

 void lkdtm_PANIC(void)
 {
 	panic("dumptest");
 }

 void lkdtm_BUG(void)
 {
 	BUG();
 }

 static int warn_counter;

 void lkdtm_WARNING(void)
 {
 	WARN_ON(++warn_counter);
 }

 void lkdtm_WARNING_MESSAGE(void)
 {
 	WARN(1, "Warning message trigger count: %d\n", ++warn_counter);
 }

 void lkdtm_EXCEPTION(void)
 {
 	*((volatile int *) 0) = 0;
 }

 void lkdtm_LOOP(void)
 {
 	for (;;)
 		;
 }

 void lkdtm_EXHAUST_STACK(void)
 {
 	pr_info("Calling function with %lu frame size to depth %d ...\n",
 		REC_STACK_SIZE, recur_count);
 	recursive_loop(recur_count);
 	pr_info("FAIL: survived without exhausting stack?!\n");
 }

 static noinline void __lkdtm_CORRUPT_STACK(void *stack)
 {
 	memset(stack, '\xff', 64);
 }

 /* This should trip the stack canary, not corrupt the return address. */
 noinline void lkdtm_CORRUPT_STACK(void)
 {
 	/* Use default char array length that triggers stack protection. */
 	char data[8] __aligned(sizeof(void *));

 	__lkdtm_CORRUPT_STACK(&data);

 	pr_info("Corrupted stack containing char array ...\n");
 }

 /* Same as above but will only get a canary with -fstack-protector-strong */
 noinline void lkdtm_CORRUPT_STACK_STRONG(void)
 {
 	union {
 		unsigned short shorts[4];
 		unsigned long *ptr;
 	} data __aligned(sizeof(void *));

 	__lkdtm_CORRUPT_STACK(&data);

 	pr_info("Corrupted stack containing union ...\n");
 }

 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
 {
 	static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
 	u32 *p;
 	u32 val = 0x12345678;

 	p = (u32 *)(data + 1);
 	if (*p == 0)
 		val = 0x87654321;
 	*p = val;
 }

 void lkdtm_SOFTLOCKUP(void)
 {
 	preempt_disable();
 	for (;;)
 		cpu_relax();
 }

 void lkdtm_HARDLOCKUP(void)
 {
 	local_irq_disable();
 	for (;;)
 		cpu_relax();
 }

 void lkdtm_SPINLOCKUP(void)
 {
 	/* Must be called twice to trigger. */
 	spin_lock(&lock_me_up);
 	/* Let sparse know we intended to exit holding the lock. */
 	__release(&lock_me_up);
 }

 void lkdtm_HUNG_TASK(void)
 {
 	set_current_state(TASK_UNINTERRUPTIBLE);
 	schedule();
 }

 void lkdtm_CORRUPT_LIST_ADD(void)
 {
 	/*
 	 * Initially, an empty list via LIST_HEAD:
 	 *	test_head.next = &test_head
 	 *	test_head.prev = &test_head
 	 */
 	LIST_HEAD(test_head);
 	struct lkdtm_list good, bad;
 	void *target[2] = { };
 	void *redirection = &target;

 	pr_info("attempting good list addition\n");

 	/*
 	 * Adding to the list performs these actions:
 	 *	test_head.next->prev = &good.node
 	 *	good.node.next = test_head.next
 	 *	good.node.prev = test_head
 	 *	test_head.next = good.node
 	 */
 	list_add(&good.node, &test_head);

 	pr_info("attempting corrupted list addition\n");
 	/*
 	 * In simulating this "write what where" primitive, the "what" is
 	 * the address of &bad.node, and the "where" is the address held
 	 * by "redirection".
 	 */
 	test_head.next = redirection;
 	list_add(&bad.node, &test_head);

 	if (target[0] == NULL && target[1] == NULL)
 		pr_err("Overwrite did not happen, but no BUG?!\n");
 	else
 		pr_err("list_add() corruption not detected!\n");
 }

 void lkdtm_CORRUPT_LIST_DEL(void)
 {
 	LIST_HEAD(test_head);
 	struct lkdtm_list item;
 	void *target[2] = { };
 	void *redirection = &target;

 	list_add(&item.node, &test_head);

 	pr_info("attempting good list removal\n");
 	list_del(&item.node);

 	pr_info("attempting corrupted list removal\n");
 	list_add(&item.node, &test_head);

 	/* As with the list_add() test above, this corrupts "next". */
 	item.node.next = redirection;
 	list_del(&item.node);

 	if (target[0] == NULL && target[1] == NULL)
 		pr_err("Overwrite did not happen, but no BUG?!\n");
 	else
 		pr_err("list_del() corruption not detected!\n");
 }

 /* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
 void lkdtm_CORRUPT_USER_DS(void)
 {
 	pr_info("setting bad task size limit\n");
 	set_fs(KERNEL_DS);

 	/* Make sure we do not keep running with a KERNEL_DS! */
 	force_sig(SIGKILL);
 }

 /* Test that VMAP_STACK is actually allocating with a leading guard page */
 void lkdtm_STACK_GUARD_PAGE_LEADING(void)
 {
 	const unsigned char *stack = task_stack_page(current);
 	const unsigned char *ptr = stack - 1;
 	volatile unsigned char byte;

 	pr_info("attempting bad read from page below current stack\n");

 	byte = *ptr;

 	pr_err("FAIL: accessed page before stack!\n");
 }

 /* Test that VMAP_STACK is actually allocating with a trailing guard page */
 void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
 {
 	const unsigned char *stack = task_stack_page(current);
 	const unsigned char *ptr = stack + THREAD_SIZE;
 	volatile unsigned char byte;

 	pr_info("attempting bad read from page above current stack\n");

 	byte = *ptr;

 	pr_err("FAIL: accessed page after stack!\n");
 }

 void lkdtm_UNSET_SMEP(void)
 {
 #ifdef CONFIG_X86_64
 #define MOV_CR4_DEPTH	64
 	void (*direct_write_cr4)(unsigned long val);
 	unsigned char *insn;
 	unsigned long cr4;
 	int i;

 	cr4 = native_read_cr4();

 	if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
 		pr_err("FAIL: SMEP not in use\n");
 		return;
 	}
 	cr4 &= ~(X86_CR4_SMEP);

 	pr_info("trying to clear SMEP normally\n");
 	native_write_cr4(cr4);
 	if (cr4 == native_read_cr4()) {
 		pr_err("FAIL: pinning SMEP failed!\n");
 		cr4 |= X86_CR4_SMEP;
 		pr_info("restoring SMEP\n");
 		native_write_cr4(cr4);
 		return;
 	}
 	pr_info("ok: SMEP did not get cleared\n");

 	/*
 	 * To test the post-write pinning verification we need to call
 	 * directly into the middle of native_write_cr4() where the
 	 * cr4 write happens, skipping any pinning. This searches for
 	 * the cr4 writing instruction.
 	 */
 	insn = (unsigned char *)native_write_cr4;
 	for (i = 0; i < MOV_CR4_DEPTH; i++) {
 		/* mov %rdi, %cr4 */
 		if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
 			break;
 		/* mov %rdi,%rax; mov %rax, %cr4 */
 		if (insn[i]   == 0x48 && insn[i+1] == 0x89 &&
 		    insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
 		    insn[i+4] == 0x22 && insn[i+5] == 0xe0)
 			break;
 	}
 	if (i >= MOV_CR4_DEPTH) {
 		pr_info("ok: cannot locate cr4 writing call gadget\n");
 		return;
 	}
 	direct_write_cr4 = (void *)(insn + i);

 	pr_info("trying to clear SMEP with call gadget\n");
 	direct_write_cr4(cr4);
 	if (native_read_cr4() & X86_CR4_SMEP) {
 		pr_info("ok: SMEP removal was reverted\n");
 	} else {
 		pr_err("FAIL: cleared SMEP not detected!\n");
 		cr4 |= X86_CR4_SMEP;
 		pr_info("restoring SMEP\n");
 		native_write_cr4(cr4);
 	}
 #else
 	pr_err("FAIL: this test is x86_64-only\n");
 #endif
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* This is for all the tests related to logic bugs (e.g. bad dereferences,
	* bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
	* lockups) along with other things that don't fit well into existing LKDTM
	* test source files.
	*/
	#include "lkdtm.h"
	#include <linux/list.h>
	#include <linux/sched.h>
	#include <linux/sched/signal.h>
	#include <linux/sched/task_stack.h>
	#include <linux/uaccess.h>

	struct lkdtm_list {
	struct list_head node;
	};

	/*
	* Make sure our attempts to over run the kernel stack doesn't trigger
	* a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
	* recurse past the end of THREAD_SIZE by default.
	*/
	#if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
	#define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
	#else
	#define REC_STACK_SIZE (THREAD_SIZE / 8)
	#endif
	#define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)

	static int recur_count = REC_NUM_DEFAULT;

	static DEFINE_SPINLOCK(lock_me_up);

	/*
	* Make sure compiler does not optimize this function or stack frame away:
	* - function marked noinline
	* - stack variables are marked volatile
	* - stack variables are written (memset()) and read (pr_info())
	* - function has external effects (pr_info())
	* */
	static int noinline recursive_loop(int remaining)
	{
	volatile char buf[REC_STACK_SIZE];

	memset((void *)buf, remaining & 0xFF, sizeof(buf));
	pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
	recur_count);
	if (!remaining)
	return 0;
	else
	return recursive_loop(remaining - 1);
	}

	/* If the depth is negative, use the default, otherwise keep parameter. */
	void __init lkdtm_bugs_init(int *recur_param)
	{
	if (*recur_param < 0)
	*recur_param = recur_count;
	else
	recur_count = *recur_param;
	}

	void lkdtm_PANIC(void)
	{
	panic("dumptest");
	}

	void lkdtm_BUG(void)
	{
	BUG();
	}

	static int warn_counter;

	void lkdtm_WARNING(void)
	{
	WARN_ON(++warn_counter);
	}

	void lkdtm_WARNING_MESSAGE(void)
	{
	WARN(1, "Warning message trigger count: %d\n", ++warn_counter);
	}

	void lkdtm_EXCEPTION(void)
	{
	((volatile int ) 0) = 0;
	}

	void lkdtm_LOOP(void)
	{
	for (;;)
	;
	}

	void lkdtm_EXHAUST_STACK(void)
	{
	pr_info("Calling function with %lu frame size to depth %d ...\n",
	REC_STACK_SIZE, recur_count);
	recursive_loop(recur_count);
	pr_info("FAIL: survived without exhausting stack?!\n");
	}

	static noinline void __lkdtm_CORRUPT_STACK(void *stack)
	{
	memset(stack, '\xff', 64);
	}

	/* This should trip the stack canary, not corrupt the return address. */
	noinline void lkdtm_CORRUPT_STACK(void)
	{
	/* Use default char array length that triggers stack protection. */
	char data[8] __aligned(sizeof(void *));

	__lkdtm_CORRUPT_STACK(&data);

	pr_info("Corrupted stack containing char array ...\n");
	}

	/* Same as above but will only get a canary with -fstack-protector-strong */
	noinline void lkdtm_CORRUPT_STACK_STRONG(void)
	{
	union {
	unsigned short shorts[4];
	unsigned long *ptr;
	} data __aligned(sizeof(void *));

	__lkdtm_CORRUPT_STACK(&data);

	pr_info("Corrupted stack containing union ...\n");
	}

	void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
	{
	static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
	u32 *p;
	u32 val = 0x12345678;

	p = (u32 *)(data + 1);
	if (*p == 0)
	val = 0x87654321;
	*p = val;
	}

	void lkdtm_SOFTLOCKUP(void)
	{
	preempt_disable();
	for (;;)
	cpu_relax();
	}

	void lkdtm_HARDLOCKUP(void)
	{
	local_irq_disable();
	for (;;)
	cpu_relax();
	}

	void lkdtm_SPINLOCKUP(void)
	{
	/* Must be called twice to trigger. */
	spin_lock(&lock_me_up);
	/* Let sparse know we intended to exit holding the lock. */
	__release(&lock_me_up);
	}

	void lkdtm_HUNG_TASK(void)
	{
	set_current_state(TASK_UNINTERRUPTIBLE);
	schedule();
	}

	void lkdtm_CORRUPT_LIST_ADD(void)
	{
	/*
	* Initially, an empty list via LIST_HEAD:
	* test_head.next = &test_head
	* test_head.prev = &test_head
	*/
	LIST_HEAD(test_head);
	struct lkdtm_list good, bad;
	void *target[2] = { };
	void *redirection = &target;

	pr_info("attempting good list addition\n");

	/*
	* Adding to the list performs these actions:
	* test_head.next->prev = &good.node
	* good.node.next = test_head.next
	* good.node.prev = test_head
	* test_head.next = good.node
	*/
	list_add(&good.node, &test_head);

	pr_info("attempting corrupted list addition\n");
	/*
	* In simulating this "write what where" primitive, the "what" is
	* the address of &bad.node, and the "where" is the address held
	* by "redirection".
	*/
	test_head.next = redirection;
	list_add(&bad.node, &test_head);

	if (target[0] == NULL && target[1] == NULL)
	pr_err("Overwrite did not happen, but no BUG?!\n");
	else
	pr_err("list_add() corruption not detected!\n");
	}

	void lkdtm_CORRUPT_LIST_DEL(void)
	{
	LIST_HEAD(test_head);
	struct lkdtm_list item;
	void *target[2] = { };
	void *redirection = &target;

	list_add(&item.node, &test_head);

	pr_info("attempting good list removal\n");
	list_del(&item.node);

	pr_info("attempting corrupted list removal\n");
	list_add(&item.node, &test_head);

	/* As with the list_add() test above, this corrupts "next". */
	item.node.next = redirection;
	list_del(&item.node);

	if (target[0] == NULL && target[1] == NULL)
	pr_err("Overwrite did not happen, but no BUG?!\n");
	else
	pr_err("list_del() corruption not detected!\n");
	}

	/* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
	void lkdtm_CORRUPT_USER_DS(void)
	{
	pr_info("setting bad task size limit\n");
	set_fs(KERNEL_DS);

	/* Make sure we do not keep running with a KERNEL_DS! */
	force_sig(SIGKILL);
	}

	/* Test that VMAP_STACK is actually allocating with a leading guard page */
	void lkdtm_STACK_GUARD_PAGE_LEADING(void)
	{
	const unsigned char *stack = task_stack_page(current);
	const unsigned char *ptr = stack - 1;
	volatile unsigned char byte;

	pr_info("attempting bad read from page below current stack\n");

	byte = *ptr;

	pr_err("FAIL: accessed page before stack!\n");
	}

	/* Test that VMAP_STACK is actually allocating with a trailing guard page */
	void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
	{
	const unsigned char *stack = task_stack_page(current);
	const unsigned char *ptr = stack + THREAD_SIZE;
	volatile unsigned char byte;

	pr_info("attempting bad read from page above current stack\n");

	byte = *ptr;

	pr_err("FAIL: accessed page after stack!\n");
	}

	void lkdtm_UNSET_SMEP(void)
	{
	#ifdef CONFIG_X86_64
	#define MOV_CR4_DEPTH 64
	void (*direct_write_cr4)(unsigned long val);
	unsigned char *insn;
	unsigned long cr4;
	int i;

	cr4 = native_read_cr4();

	if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
	pr_err("FAIL: SMEP not in use\n");
	return;
	}
	cr4 &= ~(X86_CR4_SMEP);

	pr_info("trying to clear SMEP normally\n");
	native_write_cr4(cr4);
	if (cr4 == native_read_cr4()) {
	pr_err("FAIL: pinning SMEP failed!\n");
	cr4 \|= X86_CR4_SMEP;
	pr_info("restoring SMEP\n");
	native_write_cr4(cr4);
	return;
	}
	pr_info("ok: SMEP did not get cleared\n");

	/*
	* To test the post-write pinning verification we need to call
	* directly into the middle of native_write_cr4() where the
	* cr4 write happens, skipping any pinning. This searches for
	* the cr4 writing instruction.
	*/
	insn = (unsigned char *)native_write_cr4;
	for (i = 0; i < MOV_CR4_DEPTH; i++) {
	/* mov %rdi, %cr4 */
	if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
	break;
	/* mov %rdi,%rax; mov %rax, %cr4 */
	if (insn[i] == 0x48 && insn[i+1] == 0x89 &&
	insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
	insn[i+4] == 0x22 && insn[i+5] == 0xe0)
	break;
	}
	if (i >= MOV_CR4_DEPTH) {
	pr_info("ok: cannot locate cr4 writing call gadget\n");
	return;
	}
	direct_write_cr4 = (void *)(insn + i);

	pr_info("trying to clear SMEP with call gadget\n");
	direct_write_cr4(cr4);
	if (native_read_cr4() & X86_CR4_SMEP) {
	pr_info("ok: SMEP removal was reverted\n");
	} else {
	pr_err("FAIL: cleared SMEP not detected!\n");
	cr4 \|= X86_CR4_SMEP;
	pr_info("restoring SMEP\n");
	native_write_cr4(cr4);
	}
	#else
	pr_err("FAIL: this test is x86_64-only\n");
	#endif
	}