linux-stable/kernel/kcov.c
Sebastian Andrzej Siewior d5d2c51f1e kcov: replace local_irq_save() with a local_lock_t
The kcov code mixes local_irq_save() and spin_lock() in
kcov_remote_{start|end}().  This creates a warning on PREEMPT_RT because
local_irq_save() disables interrupts and spin_lock_t is turned into a
sleeping lock which can not be acquired in a section with disabled
interrupts.

The kcov_remote_lock is used to synchronize the access to the hash-list
kcov_remote_map.  The local_irq_save() block protects access to the
per-CPU data kcov_percpu_data.

There is no compelling reason to change the lock type to raw_spin_lock_t
to make it work with local_irq_save().  Changing it would require to
move memory allocation (in kcov_remote_add()) and deallocation outside
of the locked section.

Adding an unlimited amount of entries to the hashlist will increase the
IRQ-off time during lookup.  It could be argued that this is debug code
and the latency does not matter.  There is however no need to do so and
it would allow to use this facility in an RT enabled build.

Using a local_lock_t instead of local_irq_save() has the befit of adding
a protection scope within the source which makes it obvious what is
protected.  On a !PREEMPT_RT && !LOCKDEP build the local_lock_irqsave()
maps directly to local_irq_save() so there is overhead at runtime.

Replace the local_irq_save() section with a local_lock_t.

Link: https://lkml.kernel.org/r/20210923164741.1859522-6-bigeasy@linutronix.de
Link: https://lore.kernel.org/r/20210830172627.267989-6-bigeasy@linutronix.de
Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Marco Elver <elver@google.com>
Tested-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-11-09 10:02:52 -08:00

1058 lines
28 KiB
C

// 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/hashtable.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 <linux/log2.h>
#include <asm/setup.h>
#define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
/* 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)
* - each code section for remote coverage collection
*/
refcount_t refcount;
/* The lock protects mode, size, area and t. */
spinlock_t lock;
enum kcov_mode mode;
/* Size of arena (in long's). */
unsigned int size;
/* Coverage buffer shared with user space. */
void *area;
/* Task for which we collect coverage, or NULL. */
struct task_struct *t;
/* Collecting coverage from remote (background) threads. */
bool remote;
/* Size of remote area (in long's). */
unsigned int remote_size;
/*
* Sequence is incremented each time kcov is reenabled, used by
* kcov_remote_stop(), see the comment there.
*/
int sequence;
};
struct kcov_remote_area {
struct list_head list;
unsigned int size;
};
struct kcov_remote {
u64 handle;
struct kcov *kcov;
struct hlist_node hnode;
};
static DEFINE_SPINLOCK(kcov_remote_lock);
static DEFINE_HASHTABLE(kcov_remote_map, 4);
static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
struct kcov_percpu_data {
void *irq_area;
local_lock_t lock;
unsigned int saved_mode;
unsigned int saved_size;
void *saved_area;
struct kcov *saved_kcov;
int saved_sequence;
};
static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
.lock = INIT_LOCAL_LOCK(lock),
};
/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote *kcov_remote_find(u64 handle)
{
struct kcov_remote *remote;
hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
if (remote->handle == handle)
return remote;
}
return NULL;
}
/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
{
struct kcov_remote *remote;
if (kcov_remote_find(handle))
return ERR_PTR(-EEXIST);
remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
if (!remote)
return ERR_PTR(-ENOMEM);
remote->handle = handle;
remote->kcov = kcov;
hash_add(kcov_remote_map, &remote->hnode, handle);
return remote;
}
/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
{
struct kcov_remote_area *area;
struct list_head *pos;
list_for_each(pos, &kcov_remote_areas) {
area = list_entry(pos, struct kcov_remote_area, list);
if (area->size == size) {
list_del(&area->list);
return area;
}
}
return NULL;
}
/* Must be called with kcov_remote_lock locked. */
static void kcov_remote_area_put(struct kcov_remote_area *area,
unsigned int size)
{
INIT_LIST_HEAD(&area->list);
area->size = size;
list_add(&area->list, &kcov_remote_areas);
}
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, unless we are in a remote
* coverage collection section in a softirq.
*/
if (!in_task() && !(in_serving_softirq() && t->kcov_softirq))
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_start().
*/
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_start(struct task_struct *t, struct kcov *kcov,
unsigned int size, void *area, enum kcov_mode mode,
int sequence)
{
kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
t->kcov = kcov;
/* Cache in task struct for performance. */
t->kcov_size = size;
t->kcov_area = area;
t->kcov_sequence = sequence;
/* See comment in check_kcov_mode(). */
barrier();
WRITE_ONCE(t->kcov_mode, mode);
}
static void kcov_stop(struct task_struct *t)
{
WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
barrier();
t->kcov = NULL;
t->kcov_size = 0;
t->kcov_area = NULL;
}
static void kcov_task_reset(struct task_struct *t)
{
kcov_stop(t);
t->kcov_sequence = 0;
t->kcov_handle = 0;
}
void kcov_task_init(struct task_struct *t)
{
kcov_task_reset(t);
t->kcov_handle = current->kcov_handle;
}
static void kcov_reset(struct kcov *kcov)
{
kcov->t = NULL;
kcov->mode = KCOV_MODE_INIT;
kcov->remote = false;
kcov->remote_size = 0;
kcov->sequence++;
}
static void kcov_remote_reset(struct kcov *kcov)
{
int bkt;
struct kcov_remote *remote;
struct hlist_node *tmp;
unsigned long flags;
spin_lock_irqsave(&kcov_remote_lock, flags);
hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
if (remote->kcov != kcov)
continue;
hash_del(&remote->hnode);
kfree(remote);
}
/* Do reset before unlock to prevent races with kcov_remote_start(). */
kcov_reset(kcov);
spin_unlock_irqrestore(&kcov_remote_lock, flags);
}
static void kcov_disable(struct task_struct *t, struct kcov *kcov)
{
kcov_task_reset(t);
if (kcov->remote)
kcov_remote_reset(kcov);
else
kcov_reset(kcov);
}
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)) {
kcov_remote_reset(kcov);
vfree(kcov->area);
kfree(kcov);
}
}
void kcov_task_exit(struct task_struct *t)
{
struct kcov *kcov;
unsigned long flags;
kcov = t->kcov;
if (kcov == NULL)
return;
spin_lock_irqsave(&kcov->lock, flags);
kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
/*
* For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
* which comes down to:
* WARN_ON(!kcov->remote && kcov->t != t);
*
* For KCOV_REMOTE_ENABLE devices, the exiting task is either:
*
* 1. A remote task between kcov_remote_start() and kcov_remote_stop().
* In this case we should print a warning right away, since a task
* shouldn't be exiting when it's in a kcov coverage collection
* section. Here t points to the task that is collecting remote
* coverage, and t->kcov->t points to the thread that created the
* kcov device. Which means that to detect this case we need to
* check that t != t->kcov->t, and this gives us the following:
* WARN_ON(kcov->remote && kcov->t != t);
*
* 2. The task that created kcov exiting without calling KCOV_DISABLE,
* and then again we make sure that t->kcov->t == t:
* WARN_ON(kcov->remote && kcov->t != t);
*
* By combining all three checks into one we get:
*/
if (WARN_ON(kcov->t != t)) {
spin_unlock_irqrestore(&kcov->lock, flags);
return;
}
/* Just to not leave dangling references behind. */
kcov_disable(t, kcov);
spin_unlock_irqrestore(&kcov->lock, flags);
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;
unsigned long flags;
area = vmalloc_user(vma->vm_end - vma->vm_start);
if (!area)
return -ENOMEM;
spin_lock_irqsave(&kcov->lock, flags);
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_irqrestore(&kcov->lock, flags);
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_irqrestore(&kcov->lock, flags);
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;
kcov->sequence = 1;
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;
}
static int kcov_get_mode(unsigned long arg)
{
if (arg == KCOV_TRACE_PC)
return KCOV_MODE_TRACE_PC;
else if (arg == KCOV_TRACE_CMP)
#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
return KCOV_MODE_TRACE_CMP;
#else
return -ENOTSUPP;
#endif
else
return -EINVAL;
}
/*
* 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 inline bool kcov_check_handle(u64 handle, bool common_valid,
bool uncommon_valid, bool zero_valid)
{
if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
return false;
switch (handle & KCOV_SUBSYSTEM_MASK) {
case KCOV_SUBSYSTEM_COMMON:
return (handle & KCOV_INSTANCE_MASK) ?
common_valid : zero_valid;
case KCOV_SUBSYSTEM_USB:
return uncommon_valid;
default:
return false;
}
return false;
}
static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
unsigned long arg)
{
struct task_struct *t;
unsigned long size, unused;
int mode, i;
struct kcov_remote_arg *remote_arg;
struct kcov_remote *remote;
unsigned long flags;
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;
mode = kcov_get_mode(arg);
if (mode < 0)
return mode;
kcov_fault_in_area(kcov);
kcov->mode = mode;
kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
kcov->sequence);
kcov->t = t;
/* 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_disable(t, kcov);
kcov_put(kcov);
return 0;
case KCOV_REMOTE_ENABLE:
if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
return -EINVAL;
t = current;
if (kcov->t != NULL || t->kcov != NULL)
return -EBUSY;
remote_arg = (struct kcov_remote_arg *)arg;
mode = kcov_get_mode(remote_arg->trace_mode);
if (mode < 0)
return mode;
if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
return -EINVAL;
kcov->mode = mode;
t->kcov = kcov;
kcov->t = t;
kcov->remote = true;
kcov->remote_size = remote_arg->area_size;
spin_lock_irqsave(&kcov_remote_lock, flags);
for (i = 0; i < remote_arg->num_handles; i++) {
if (!kcov_check_handle(remote_arg->handles[i],
false, true, false)) {
spin_unlock_irqrestore(&kcov_remote_lock,
flags);
kcov_disable(t, kcov);
return -EINVAL;
}
remote = kcov_remote_add(kcov, remote_arg->handles[i]);
if (IS_ERR(remote)) {
spin_unlock_irqrestore(&kcov_remote_lock,
flags);
kcov_disable(t, kcov);
return PTR_ERR(remote);
}
}
if (remote_arg->common_handle) {
if (!kcov_check_handle(remote_arg->common_handle,
true, false, false)) {
spin_unlock_irqrestore(&kcov_remote_lock,
flags);
kcov_disable(t, kcov);
return -EINVAL;
}
remote = kcov_remote_add(kcov,
remote_arg->common_handle);
if (IS_ERR(remote)) {
spin_unlock_irqrestore(&kcov_remote_lock,
flags);
kcov_disable(t, kcov);
return PTR_ERR(remote);
}
t->kcov_handle = remote_arg->common_handle;
}
spin_unlock_irqrestore(&kcov_remote_lock, flags);
/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
kcov_get(kcov);
return 0;
default:
return -ENOTTY;
}
}
static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
struct kcov *kcov;
int res;
struct kcov_remote_arg *remote_arg = NULL;
unsigned int remote_num_handles;
unsigned long remote_arg_size;
unsigned long flags;
if (cmd == KCOV_REMOTE_ENABLE) {
if (get_user(remote_num_handles, (unsigned __user *)(arg +
offsetof(struct kcov_remote_arg, num_handles))))
return -EFAULT;
if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
return -EINVAL;
remote_arg_size = struct_size(remote_arg, handles,
remote_num_handles);
remote_arg = memdup_user((void __user *)arg, remote_arg_size);
if (IS_ERR(remote_arg))
return PTR_ERR(remote_arg);
if (remote_arg->num_handles != remote_num_handles) {
kfree(remote_arg);
return -EINVAL;
}
arg = (unsigned long)remote_arg;
}
kcov = filep->private_data;
spin_lock_irqsave(&kcov->lock, flags);
res = kcov_ioctl_locked(kcov, cmd, arg);
spin_unlock_irqrestore(&kcov->lock, flags);
kfree(remote_arg);
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,
};
/*
* kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
* of code in a kernel background thread or in a softirq to allow kcov to be
* used to collect coverage from that part of code.
*
* The handle argument of kcov_remote_start() identifies a code section that is
* used for coverage collection. A userspace process passes this handle to
* KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
* coverage for the code section identified by this handle.
*
* The usage of these annotations in the kernel code is different depending on
* the type of the kernel thread whose code is being annotated.
*
* For global kernel threads that are spawned in a limited number of instances
* (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
* softirqs, each instance must be assigned a unique 4-byte instance id. The
* instance id is then combined with a 1-byte subsystem id to get a handle via
* kcov_remote_handle(subsystem_id, instance_id).
*
* For local kernel threads that are spawned from system calls handler when a
* user interacts with some kernel interface (e.g. vhost workers), a handle is
* passed from a userspace process as the common_handle field of the
* kcov_remote_arg struct (note, that the user must generate a handle by using
* kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
* arbitrary 4-byte non-zero number as the instance id). This common handle
* then gets saved into the task_struct of the process that issued the
* KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
* kernel threads, the common handle must be retrieved via kcov_common_handle()
* and passed to the spawned threads via custom annotations. Those kernel
* threads must in turn be annotated with kcov_remote_start(common_handle) and
* kcov_remote_stop(). All of the threads that are spawned by the same process
* obtain the same handle, hence the name "common".
*
* See Documentation/dev-tools/kcov.rst for more details.
*
* Internally, kcov_remote_start() looks up the kcov device associated with the
* provided handle, allocates an area for coverage collection, and saves the
* pointers to kcov and area into the current task_struct to allow coverage to
* be collected via __sanitizer_cov_trace_pc().
* In turns kcov_remote_stop() clears those pointers from task_struct to stop
* collecting coverage and copies all collected coverage into the kcov area.
*/
static inline bool kcov_mode_enabled(unsigned int mode)
{
return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
}
static void kcov_remote_softirq_start(struct task_struct *t)
{
struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
unsigned int mode;
mode = READ_ONCE(t->kcov_mode);
barrier();
if (kcov_mode_enabled(mode)) {
data->saved_mode = mode;
data->saved_size = t->kcov_size;
data->saved_area = t->kcov_area;
data->saved_sequence = t->kcov_sequence;
data->saved_kcov = t->kcov;
kcov_stop(t);
}
}
static void kcov_remote_softirq_stop(struct task_struct *t)
{
struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
if (data->saved_kcov) {
kcov_start(t, data->saved_kcov, data->saved_size,
data->saved_area, data->saved_mode,
data->saved_sequence);
data->saved_mode = 0;
data->saved_size = 0;
data->saved_area = NULL;
data->saved_sequence = 0;
data->saved_kcov = NULL;
}
}
void kcov_remote_start(u64 handle)
{
struct task_struct *t = current;
struct kcov_remote *remote;
struct kcov *kcov;
unsigned int mode;
void *area;
unsigned int size;
int sequence;
unsigned long flags;
if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
return;
if (!in_task() && !in_serving_softirq())
return;
local_lock_irqsave(&kcov_percpu_data.lock, flags);
/*
* Check that kcov_remote_start() is not called twice in background
* threads nor called by user tasks (with enabled kcov).
*/
mode = READ_ONCE(t->kcov_mode);
if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
/*
* Check that kcov_remote_start() is not called twice in softirqs.
* Note, that kcov_remote_start() can be called from a softirq that
* happened while collecting coverage from a background thread.
*/
if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
spin_lock(&kcov_remote_lock);
remote = kcov_remote_find(handle);
if (!remote) {
spin_unlock(&kcov_remote_lock);
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
kcov_debug("handle = %llx, context: %s\n", handle,
in_task() ? "task" : "softirq");
kcov = remote->kcov;
/* Put in kcov_remote_stop(). */
kcov_get(kcov);
/*
* Read kcov fields before unlock to prevent races with
* KCOV_DISABLE / kcov_remote_reset().
*/
mode = kcov->mode;
sequence = kcov->sequence;
if (in_task()) {
size = kcov->remote_size;
area = kcov_remote_area_get(size);
} else {
size = CONFIG_KCOV_IRQ_AREA_SIZE;
area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
}
spin_unlock(&kcov_remote_lock);
/* Can only happen when in_task(). */
if (!area) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
area = vmalloc(size * sizeof(unsigned long));
if (!area) {
kcov_put(kcov);
return;
}
local_lock_irqsave(&kcov_percpu_data.lock, flags);
}
/* Reset coverage size. */
*(u64 *)area = 0;
if (in_serving_softirq()) {
kcov_remote_softirq_start(t);
t->kcov_softirq = 1;
}
kcov_start(t, kcov, size, area, mode, sequence);
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
}
EXPORT_SYMBOL(kcov_remote_start);
static void kcov_move_area(enum kcov_mode mode, void *dst_area,
unsigned int dst_area_size, void *src_area)
{
u64 word_size = sizeof(unsigned long);
u64 count_size, entry_size_log;
u64 dst_len, src_len;
void *dst_entries, *src_entries;
u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
kcov_debug("%px %u <= %px %lu\n",
dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
switch (mode) {
case KCOV_MODE_TRACE_PC:
dst_len = READ_ONCE(*(unsigned long *)dst_area);
src_len = *(unsigned long *)src_area;
count_size = sizeof(unsigned long);
entry_size_log = __ilog2_u64(sizeof(unsigned long));
break;
case KCOV_MODE_TRACE_CMP:
dst_len = READ_ONCE(*(u64 *)dst_area);
src_len = *(u64 *)src_area;
count_size = sizeof(u64);
BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
break;
default:
WARN_ON(1);
return;
}
/* As arm can't divide u64 integers use log of entry size. */
if (dst_len > ((dst_area_size * word_size - count_size) >>
entry_size_log))
return;
dst_occupied = count_size + (dst_len << entry_size_log);
dst_free = dst_area_size * word_size - dst_occupied;
bytes_to_move = min(dst_free, src_len << entry_size_log);
dst_entries = dst_area + dst_occupied;
src_entries = src_area + count_size;
memcpy(dst_entries, src_entries, bytes_to_move);
entries_moved = bytes_to_move >> entry_size_log;
switch (mode) {
case KCOV_MODE_TRACE_PC:
WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
break;
case KCOV_MODE_TRACE_CMP:
WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
break;
default:
break;
}
}
/* See the comment before kcov_remote_start() for usage details. */
void kcov_remote_stop(void)
{
struct task_struct *t = current;
struct kcov *kcov;
unsigned int mode;
void *area;
unsigned int size;
int sequence;
unsigned long flags;
if (!in_task() && !in_serving_softirq())
return;
local_lock_irqsave(&kcov_percpu_data.lock, flags);
mode = READ_ONCE(t->kcov_mode);
barrier();
if (!kcov_mode_enabled(mode)) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
/*
* When in softirq, check if the corresponding kcov_remote_start()
* actually found the remote handle and started collecting coverage.
*/
if (in_serving_softirq() && !t->kcov_softirq) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
/* Make sure that kcov_softirq is only set when in softirq. */
if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
return;
}
kcov = t->kcov;
area = t->kcov_area;
size = t->kcov_size;
sequence = t->kcov_sequence;
kcov_stop(t);
if (in_serving_softirq()) {
t->kcov_softirq = 0;
kcov_remote_softirq_stop(t);
}
spin_lock(&kcov->lock);
/*
* KCOV_DISABLE could have been called between kcov_remote_start()
* and kcov_remote_stop(), hence the sequence check.
*/
if (sequence == kcov->sequence && kcov->remote)
kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
spin_unlock(&kcov->lock);
if (in_task()) {
spin_lock(&kcov_remote_lock);
kcov_remote_area_put(area, size);
spin_unlock(&kcov_remote_lock);
}
local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
/* Get in kcov_remote_start(). */
kcov_put(kcov);
}
EXPORT_SYMBOL(kcov_remote_stop);
/* See the comment before kcov_remote_start() for usage details. */
u64 kcov_common_handle(void)
{
if (!in_task())
return 0;
return current->kcov_handle;
}
EXPORT_SYMBOL(kcov_common_handle);
static int __init kcov_init(void)
{
int cpu;
for_each_possible_cpu(cpu) {
void *area = vmalloc_node(CONFIG_KCOV_IRQ_AREA_SIZE *
sizeof(unsigned long), cpu_to_node(cpu));
if (!area)
return -ENOMEM;
per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
}
/*
* 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);