// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) "kcov: " fmt
#define DISABLE_BRANCH_PROFILING
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/types.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/preempt.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/kcov.h>
#include <linux/refcount.h>
#include <asm/setup.h>
/* Number of 64-bit words written per one comparison: */
#define KCOV_WORDS_PER_CMP 4
/*
* kcov descriptor (one per opened debugfs file).
* State transitions of the descriptor:
* - initial state after open()
* - then there must be a single ioctl(KCOV_INIT_TRACE) call
* - then, mmap() call (several calls are allowed but not useful)
* - then, ioctl(KCOV_ENABLE, arg), where arg is
* KCOV_TRACE_PC - to trace only the PCs
* or
* KCOV_TRACE_CMP - to trace only the comparison operands
* - then, ioctl(KCOV_DISABLE) to disable the task.
* Enabling/disabling ioctls can be repeated (only one task a time allowed).
*/
struct kcov {
/*
* Reference counter. We keep one for:
* - opened file descriptor
* - task with enabled coverage (we can't unwire it from another task)
*/
refcount_t refcount;
/* The lock protects mode, size, area and t. */
spinlock_t lock;
enum kcov_mode mode;
/* Size of arena (in long's for KCOV_MODE_TRACE). */
unsigned size;
/* Coverage buffer shared with user space. */
void *area;
/* Task for which we collect coverage, or NULL. */
struct task_struct *t;
};
static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
{
unsigned int mode;
/*
* We are interested in code coverage as a function of a syscall inputs,
* so we ignore code executed in interrupts.
*/
if (!in_task())
return false;
mode = READ_ONCE(t->kcov_mode);
/*
* There is some code that runs in interrupts but for which
* in_interrupt() returns false (e.g. preempt_schedule_irq()).
* READ_ONCE()/barrier() effectively provides load-acquire wrt
* interrupts, there are paired barrier()/WRITE_ONCE() in
* kcov_ioctl_locked().
*/
barrier();
return mode == needed_mode;
}
static notrace unsigned long canonicalize_ip(unsigned long ip)
{
#ifdef CONFIG_RANDOMIZE_BASE
ip -= kaslr_offset();
#endif
return ip;
}
/*
* Entry point from instrumented code.
* This is called once per basic-block/edge.
*/
void notrace __sanitizer_cov_trace_pc(void)
{
struct task_struct *t;
unsigned long *area;
unsigned long ip = canonicalize_ip(_RET_IP_);
unsigned long pos;
t = current;
if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
return;
area = t->kcov_area;
/* The first 64-bit word is the number of subsequent PCs. */
pos = READ_ONCE(area[0]) + 1;
if (likely(pos < t->kcov_size)) {
area[pos] = ip;
WRITE_ONCE(area[0], pos);
}
}
EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
{
struct task_struct *t;
u64 *area;
u64 count, start_index, end_pos, max_pos;
t = current;
if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
return;
ip = canonicalize_ip(ip);
/*
* We write all comparison arguments and types as u64.
* The buffer was allocated for t->kcov_size unsigned longs.
*/
area = (u64 *)t->kcov_area;
max_pos = t->kcov_size * sizeof(unsigned long);
count = READ_ONCE(area[0]);
/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
start_index = 1 + count * KCOV_WORDS_PER_CMP;
end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
if (likely(end_pos <= max_pos)) {
area[start_index] = type;
area[start_index + 1] = arg1;
area[start_index + 2] = arg2;
area[start_index + 3] = ip;
WRITE_ONCE(area[0], count + 1);
}
}
void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
{
write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
{
write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
{
write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
{
write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
{
write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
{
write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
{
write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
{
write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
{
u64 i;
u64 count = cases[0];
u64 size = cases[1];
u64 type = KCOV_CMP_CONST;
switch (size) {
case 8:
type |= KCOV_CMP_SIZE(0);
break;
case 16:
type |= KCOV_CMP_SIZE(1);
break;
case 32:
type |= KCOV_CMP_SIZE(2);
break;
case 64:
type |= KCOV_CMP_SIZE(3);
break;
default:
return;
}
for (i = 0; i < count; i++)
write_comp_data(type, cases[i + 2], val, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
static void kcov_get(struct kcov *kcov)
{
refcount_inc(&kcov->refcount);
}
static void kcov_put(struct kcov *kcov)
{
if (refcount_dec_and_test(&kcov->refcount)) {
vfree(kcov->area);
kfree(kcov);
}
}
void kcov_task_init(struct task_struct *t)
{
WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
barrier();
t->kcov_size = 0;
t->kcov_area = NULL;
t->kcov = NULL;
}
void kcov_task_exit(struct task_struct *t)
{
struct kcov *kcov;
kcov = t->kcov;
if (kcov == NULL)
return;
spin_lock(&kcov->lock);
if (WARN_ON(kcov->t != t)) {
spin_unlock(&kcov->lock);
return;
}
/* Just to not leave dangling references behind. */
kcov_task_init(t);
kcov->t = NULL;
kcov->mode = KCOV_MODE_INIT;
spin_unlock(&kcov->lock);
kcov_put(kcov);
}
static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
{
int res = 0;
void *area;
struct kcov *kcov = vma->vm_file->private_data;
unsigned long size, off;
struct page *page;
area = vmalloc_user(vma->vm_end - vma->vm_start);
if (!area)
return -ENOMEM;
spin_lock(&kcov->lock);
size = kcov->size * sizeof(unsigned long);
if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
vma->vm_end - vma->vm_start != size) {
res = -EINVAL;
goto exit;
}
if (!kcov->area) {
kcov->area = area;
vma->vm_flags |= VM_DONTEXPAND;
spin_unlock(&kcov->lock);
for (off = 0; off < size; off += PAGE_SIZE) {
page = vmalloc_to_page(kcov->area + off);
if (vm_insert_page(vma, vma->vm_start + off, page))
WARN_ONCE(1, "vm_insert_page() failed");
}
return 0;
}
exit:
spin_unlock(&kcov->lock);
vfree(area);
return res;
}
static int kcov_open(struct inode *inode, struct file *filep)
{
struct kcov *kcov;
kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
if (!kcov)
return -ENOMEM;
kcov->mode = KCOV_MODE_DISABLED;
refcount_set(&kcov->refcount, 1);
spin_lock_init(&kcov->lock);
filep->private_data = kcov;
return nonseekable_open(inode, filep);
}
static int kcov_close(struct inode *inode, struct file *filep)
{
kcov_put(filep->private_data);
return 0;
}
/*
* Fault in a lazily-faulted vmalloc area before it can be used by
* __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
* vmalloc fault handling path is instrumented.
*/
static void kcov_fault_in_area(struct kcov *kcov)
{
unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
unsigned long *area = kcov->area;
unsigned long offset;
for (offset = 0; offset < kcov->size; offset += stride)
READ_ONCE(area[offset]);
}
static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
unsigned long arg)
{
struct task_struct *t;
unsigned long size, unused;
switch (cmd) {
case KCOV_INIT_TRACE:
/*
* Enable kcov in trace mode and setup buffer size.
* Must happen before anything else.
*/
if (kcov->mode != KCOV_MODE_DISABLED)
return -EBUSY;
/*
* Size must be at least 2 to hold current position and one PC.
* Later we allocate size * sizeof(unsigned long) memory,
* that must not overflow.
*/
size = arg;
if (size < 2 || size > INT_MAX / sizeof(unsigned long))
return -EINVAL;
kcov->size = size;
kcov->mode = KCOV_MODE_INIT;
return 0;
case KCOV_ENABLE:
/*
* Enable coverage for the current task.
* At this point user must have been enabled trace mode,
* and mmapped the file. Coverage collection is disabled only
* at task exit or voluntary by KCOV_DISABLE. After that it can
* be enabled for another task.
*/
if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
return -EINVAL;
t = current;
if (kcov->t != NULL || t->kcov != NULL)
return -EBUSY;
if (arg == KCOV_TRACE_PC)
kcov->mode = KCOV_MODE_TRACE_PC;
else if (arg == KCOV_TRACE_CMP)
#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
kcov->mode = KCOV_MODE_TRACE_CMP;
#else
return -ENOTSUPP;
#endif
else
return -EINVAL;
kcov_fault_in_area(kcov);
/* Cache in task struct for performance. */
t->kcov_size = kcov->size;
t->kcov_area = kcov->area;
/* See comment in check_kcov_mode(). */
barrier();
WRITE_ONCE(t->kcov_mode, kcov->mode);
t->kcov = kcov;
kcov->t = t;
/* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
kcov_get(kcov);
return 0;
case KCOV_DISABLE:
/* Disable coverage for the current task. */
unused = arg;
if (unused != 0 || current->kcov != kcov)
return -EINVAL;
t = current;
if (WARN_ON(kcov->t != t))
return -EINVAL;
kcov_task_init(t);
kcov->t = NULL;
kcov->mode = KCOV_MODE_INIT;
kcov_put(kcov);
return 0;
default:
return -ENOTTY;
}
}
static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
struct kcov *kcov;
int res;
kcov = filep->private_data;
spin_lock(&kcov->lock);
res = kcov_ioctl_locked(kcov, cmd, arg);
spin_unlock(&kcov->lock);
return res;
}
static const struct file_operations kcov_fops = {
.open = kcov_open,
.unlocked_ioctl = kcov_ioctl,
.compat_ioctl = kcov_ioctl,
.mmap = kcov_mmap,
.release = kcov_close,
};
static int __init kcov_init(void)
{
/*
* The kcov debugfs file won't ever get removed and thus,
* there is no need to protect it against removal races. The
* use of debugfs_create_file_unsafe() is actually safe here.
*/
debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
return 0;
}
device_initcall(kcov_init);
