cregit-Linux how code gets into the kernel

Release 4.7 kernel/kcov.c

Directory: kernel

#define pr_fmt(fmt) "kcov: " fmt


#define DISABLE_BRANCH_PROFILING
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/printk.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>

/*
 * 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, repeated enable/disable for a task (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;
};

/*
 * Entry point from instrumented code.
 * This is called once per basic-block/edge.
 */

void notrace __sanitizer_cov_trace_pc(void) { struct task_struct *t; enum kcov_mode mode; t = current; /* * We are interested in code coverage as a function of a syscall inputs, * so we ignore code executed in interrupts. */ if (!t || in_interrupt()) return; mode = READ_ONCE(t->kcov_mode); if (mode == KCOV_MODE_TRACE) { unsigned long *area; unsigned long pos; /* * 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(); area = t->kcov_area; /* The first word is number of subsequent PCs. */ pos = READ_ONCE(area[0]) + 1; if (likely(pos < t->kcov_size)) { area[pos] = _RET_IP_; WRITE_ONCE(area[0], pos); } } }

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EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
static void kcov_get(struct kcov *kcov) { atomic_inc(&kcov->refcount); }

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static void kcov_put(struct kcov *kcov) { if (atomic_dec_and_test(&kcov->refcount)) { vfree(kcov->area); kfree(kcov); } }

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void kcov_task_init(struct task_struct *t) { t->kcov_mode = KCOV_MODE_DISABLED; t->kcov_size = 0; t->kcov_area = NULL; t->kcov = NULL; }

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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; spin_unlock(&kcov->lock); kcov_put(kcov); }

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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_DISABLED || 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; }

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static int kcov_open(struct inode *inode, struct file *filep) { struct kcov *kcov; kcov = kzalloc(sizeof(*kcov), GFP_KERNEL); if (!kcov) return -ENOMEM; atomic_set(&kcov->refcount, 1); spin_lock_init(&kcov->lock); filep->private_data = kcov; return nonseekable_open(inode, filep); }

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static int kcov_close(struct inode *inode, struct file *filep) { kcov_put(filep->private_data); return 0; }

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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_TRACE; 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. */ unused = arg; if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED || kcov->area == NULL) return -EINVAL; if (kcov->t != NULL) return -EBUSY; t = current; /* Cache in task struct for performance. */ t->kcov_size = kcov->size; t->kcov_area = kcov->area; /* See comment in __sanitizer_cov_trace_pc(). */ 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_put(kcov); return 0; default: return -ENOTTY; } }

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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; }

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static const struct file_operations kcov_fops = { .open = kcov_open, .unlocked_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; }

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device_initcall(kcov_init);

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Directory: kernel
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