Commit 6556fde2 authored by Marco Elver's avatar Marco Elver Committed by Peter Zijlstra
Browse files

kcov: Enable context analysis 



Enable context analysis for the KCOV subsystem.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-30-elver@google.com
parent 0f5d7648

kernel/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -43,6 +43,8 @@ KASAN_SANITIZE_kcov.o := n 
KCSAN_SANITIZE_kcov.o := n

UBSAN_SANITIZE_kcov.o := n

KMSAN_SANITIZE_kcov.o := n



CONTEXT_ANALYSIS_kcov.o := y

CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector



obj-y += sched/

kernel/kcov.c

+25 −11
Original line number Diff line number Diff line
@@ -55,13 +55,13 @@ struct kcov { 
	refcount_t		refcount;

	/* The lock protects mode, size, area and t. */

	spinlock_t		lock;

	enum kcov_mode		mode;

	enum kcov_mode		mode __guarded_by(&lock);

	/* Size of arena (in long's). */

	unsigned int		size;

	unsigned int		size __guarded_by(&lock);

	/* Coverage buffer shared with user space. */

	void			*area;

	void			*area __guarded_by(&lock);

	/* Task for which we collect coverage, or NULL. */

	struct task_struct	*t;

	struct task_struct	*t __guarded_by(&lock);

	/* Collecting coverage from remote (background) threads. */

	bool			remote;

	/* Size of remote area (in long's). */
@@ -391,6 +391,7 @@ void kcov_task_init(struct task_struct *t) 
}



static void kcov_reset(struct kcov *kcov)

	__must_hold(&kcov->lock)

{

	kcov->t = NULL;

	kcov->mode = KCOV_MODE_INIT;
@@ -400,6 +401,7 @@ static void kcov_reset(struct kcov *kcov) 
}



static void kcov_remote_reset(struct kcov *kcov)

	__must_hold(&kcov->lock)

{

	int bkt;

	struct kcov_remote *remote;
@@ -419,6 +421,7 @@ static void kcov_remote_reset(struct kcov *kcov) 
}



static void kcov_disable(struct task_struct *t, struct kcov *kcov)

	__must_hold(&kcov->lock)

{

	kcov_task_reset(t);

	if (kcov->remote)
@@ -435,8 +438,11 @@ static void kcov_get(struct kcov *kcov) 
static void kcov_put(struct kcov *kcov)

{

	if (refcount_dec_and_test(&kcov->refcount)) {

		/* Context-safety: no references left, object being destroyed. */

		context_unsafe(

			kcov_remote_reset(kcov);

			vfree(kcov->area);

		);

		kfree(kcov);

	}

}
@@ -491,6 +497,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma) 
	unsigned long size, off;

	struct page *page;

	unsigned long flags;

	void *area;



	spin_lock_irqsave(&kcov->lock, flags);

	size = kcov->size * sizeof(unsigned long);
@@ -499,10 +506,11 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma) 
		res = -EINVAL;

		goto exit;

	}

	area = kcov->area;

	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);

		page = vmalloc_to_page(area + off);

		res = vm_insert_page(vma, vma->vm_start + off, page);

		if (res) {

			pr_warn_once("kcov: vm_insert_page() failed\n");
@@ -522,10 +530,10 @@ static int kcov_open(struct inode *inode, struct file *filep) 
	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);

	if (!kcov)

		return -ENOMEM;

	spin_lock_init(&kcov->lock);

	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);

}
@@ -556,6 +564,7 @@ static int kcov_get_mode(unsigned long arg) 
 * vmalloc fault handling path is instrumented.

 */

static void kcov_fault_in_area(struct kcov *kcov)

	__must_hold(&kcov->lock)

{

	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);

	unsigned long *area = kcov->area;
@@ -584,6 +593,7 @@ static inline bool kcov_check_handle(u64 handle, bool common_valid, 


static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,

			     unsigned long arg)

	__must_hold(&kcov->lock)

{

	struct task_struct *t;

	unsigned long flags, unused;
@@ -814,6 +824,7 @@ static inline bool kcov_mode_enabled(unsigned int mode) 
}



static void kcov_remote_softirq_start(struct task_struct *t)

	__must_hold(&kcov_percpu_data.lock)

{

	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);

	unsigned int mode;
@@ -831,6 +842,7 @@ static void kcov_remote_softirq_start(struct task_struct *t) 
}



static void kcov_remote_softirq_stop(struct task_struct *t)

	__must_hold(&kcov_percpu_data.lock)

{

	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
@@ -896,10 +908,12 @@ void kcov_remote_start(u64 handle) 
	/* Put in kcov_remote_stop(). */

	kcov_get(kcov);

	/*

	 * Read kcov fields before unlock to prevent races with

	 * KCOV_DISABLE / kcov_remote_reset().

	 * Read kcov fields before unlocking kcov_remote_lock to prevent races

	 * with KCOV_DISABLE and kcov_remote_reset(); cannot acquire kcov->lock

	 * here, because it might lead to deadlock given kcov_remote_lock is

	 * acquired _after_ kcov->lock elsewhere.

	 */

	mode = kcov->mode;

	mode = context_unsafe(kcov->mode);

	sequence = kcov->sequence;

	if (in_task()) {

		size = kcov->remote_size;