blob: de0c54c8fac3e9bc166dcbd4ebbe7e59bb18bdd2 [file] [log] [blame]
// 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/sched.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>
#ifdef CONFIG_X86_32
#include <asm/desc.h>
#endif
/*
* 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();
}
/* 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)
{
#if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML)
#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("XFAIL: this test is x86_64-only\n");
#endif
}
void lkdtm_DOUBLE_FAULT(void)
{
#ifdef CONFIG_X86_32
/*
* Trigger #DF by setting the stack limit to zero. This clobbers
* a GDT TLS slot, which is okay because the current task will die
* anyway due to the double fault.
*/
struct desc_struct d = {
.type = 3, /* expand-up, writable, accessed data */
.p = 1, /* present */
.d = 1, /* 32-bit */
.g = 0, /* limit in bytes */
.s = 1, /* not system */
};
local_irq_disable();
write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()),
GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S);
/*
* Put our zero-limit segment in SS and then trigger a fault. The
* 4-byte access to (%esp) will fault with #SS, and the attempt to
* deliver the fault will recursively cause #SS and result in #DF.
* This whole process happens while NMIs and MCEs are blocked by the
* MOV SS window. This is nice because an NMI with an invalid SS
* would also double-fault, resulting in the NMI or MCE being lost.
*/
asm volatile ("movw %0, %%ss; addl $0, (%%esp)" ::
"r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3)));
pr_err("FAIL: tried to double fault but didn't die\n");
#else
pr_err("XFAIL: this test is ia32-only\n");
#endif
}