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32 results

kcov.c

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  • kcov.c 11.07 KiB
    // 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);