1 files changed, 454 insertions, 0 deletions
diff --git a/kernel/kcov.c b/kernel/kcov.c
new file mode 100644
index 000000000..c2277dbdb
--- /dev/null
+++ b/kernel/kcov.c
@@ -0,0 +1,454 @@
+// 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 <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)
+	 */
+	atomic_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)
+{
+	atomic_inc(&kcov->refcount);
+}
+
+static void kcov_put(struct kcov *kcov)
+{
+	if (atomic_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;
+	atomic_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.
+	 */
+	if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
+		pr_err("failed to create kcov in debugfs\n");
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+device_initcall(kcov_init);