cregit-Linux how code gets into the kernel

Release 4.15 kernel/kcov.c

Directory: kernel
// 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 bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t) { enum kcov_mode 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; }

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static unsigned long canonicalize_ip(unsigned long ip) { #ifdef CONFIG_RANDOMIZE_BASE ip -= kaslr_offset(); #endif return ip; }

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/* * 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); } }

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EXPORT_SYMBOL(__sanitizer_cov_trace_pc); #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
static void 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); } }

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void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2) { write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_); }

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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_); }

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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_); }

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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_); }

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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_); }

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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_); }

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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_); }

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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_); }

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James Morse13.57%133.33%
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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_); }

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EXPORT_SYMBOL(__sanitizer_cov_trace_switch); #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
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; kcov->mode = KCOV_MODE_INIT; spin_unlock(&kcov->lock); kcov_put(kcov); }

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Dmitriy Vyukov8393.26%150.00%
Victor Chibotaru66.74%150.00%
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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_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; }

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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; kcov->mode = KCOV_MODE_DISABLED; 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_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; if (kcov->t != 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; t = current; /* 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; } }

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Dmitriy Vyukov24482.43%150.00%
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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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Dmitriy Vyukov63100.00%1100.00%
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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; }

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device_initcall(kcov_init);

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Victor Chibotaru76342.94%19.09%
Kefeng Wang181.01%218.18%
Alexander Popov50.28%19.09%
Andrey Ryabinin30.17%19.09%
Nicolai Stange20.11%19.09%
Greg Kroah-Hartman10.06%19.09%
James Morse10.06%19.09%
Total1777100.00%11100.00%
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