diff options
Diffstat (limited to 'kernel/kcov.c')
| -rw-r--r-- | kernel/kcov.c | 1081 |
1 files changed, 1081 insertions, 0 deletions
diff --git a/kernel/kcov.c b/kernel/kcov.c new file mode 100644 index 0000000000..f9ac2e9e46 --- /dev/null +++ b/kernel/kcov.c @@ -0,0 +1,1081 @@ +// 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/kmsan-checks.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); + /* + * KMSAN doesn't instrument this file, so it may not know area->list + * is initialized. Unpoison it explicitly to avoid reports in + * kcov_remote_area_get(). + */ + kmsan_unpoison_memory(&area->list, sizeof(area->list)); +} + +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)) { + /* Previously we write pc before updating pos. However, some + * early interrupt code could bypass check_kcov_mode() check + * and invoke __sanitizer_cov_trace_pc(). If such interrupt is + * raised between writing pc and updating pos, the pc could be + * overitten by the recursive __sanitizer_cov_trace_pc(). + * Update pos before writing pc to avoid such interleaving. + */ + WRITE_ONCE(area[0], pos); + barrier(); + area[pos] = ip; + } +} +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)) { + /* See comment in __sanitizer_cov_trace_pc(). */ + WRITE_ONCE(area[0], count + 1); + barrier(); + area[start_index] = type; + area[start_index + 1] = arg1; + area[start_index + 2] = arg2; + area[start_index + 3] = ip; + } +} + +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(kcov_u64 arg1, kcov_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(kcov_u64 arg1, kcov_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(kcov_u64 val, void *arg) +{ + u64 i; + u64 *cases = arg; + 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; + struct kcov *kcov = vma->vm_file->private_data; + unsigned long size, off; + struct page *page; + unsigned long flags; + + spin_lock_irqsave(&kcov->lock, flags); + size = kcov->size * sizeof(unsigned long); + if (kcov->area == NULL || vma->vm_pgoff != 0 || + vma->vm_end - vma->vm_start != size) { + res = -EINVAL; + goto exit; + } + spin_unlock_irqrestore(&kcov->lock, flags); + vm_flags_set(vma, VM_DONTEXPAND); + for (off = 0; off < size; off += PAGE_SIZE) { + page = vmalloc_to_page(kcov->area + off); + res = vm_insert_page(vma, vma->vm_start + off, page); + if (res) { + pr_warn_once("kcov: vm_insert_page() failed\n"); + return res; + } + } + return 0; +exit: + spin_unlock_irqrestore(&kcov->lock, flags); + 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 flags, unused; + int mode, i; + struct kcov_remote_arg *remote_arg; + struct kcov_remote *remote; + + switch (cmd) { + 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 size, flags; + void *area; + + kcov = filep->private_data; + switch (cmd) { + case KCOV_INIT_TRACE: + /* + * Enable kcov in trace mode and setup buffer size. + * Must happen before anything else. + * + * First check the size argument - it must be at least 2 + * to hold the current position and one PC. + */ + size = arg; + if (size < 2 || size > INT_MAX / sizeof(unsigned long)) + return -EINVAL; + area = vmalloc_user(size * sizeof(unsigned long)); + if (area == NULL) + return -ENOMEM; + spin_lock_irqsave(&kcov->lock, flags); + if (kcov->mode != KCOV_MODE_DISABLED) { + spin_unlock_irqrestore(&kcov->lock, flags); + vfree(area); + return -EBUSY; + } + kcov->area = area; + kcov->size = size; + kcov->mode = KCOV_MODE_INIT; + spin_unlock_irqrestore(&kcov->lock, flags); + return 0; + case 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; + fallthrough; + default: + /* + * All other commands can be normally executed under a spin lock, so we + * obtain and release it here in order to simplify kcov_ioctl_locked(). + */ + 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); |