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Subject[PATCH v3 2/2] kcov: properly handle subsequent mmap calls
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Allocate the kcov buffer during KCOV_MODE_INIT in order to untie mmapping
of a kcov instance and the actual coverage collection process. Modify
kcov_mmap, so that it can be reliably used any number of times once
KCOV_MODE_INIT has succeeded.

These changes to the user-facing interface of the tool only weaken the
preconditions, so all existing user space code should remain compatible
with the new version.

Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
---
kernel/kcov.c | 34 +++++++++++++++-------------------
1 file changed, 15 insertions(+), 19 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index e1be7301500b..475524bd900a 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -459,37 +459,28 @@ void kcov_task_exit(struct task_struct *t)
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;
unsigned long flags;

- area = vmalloc_user(vma->vm_end - vma->vm_start);
- if (!area)
- return -ENOMEM;
-
spin_lock_irqsave(&kcov->lock, flags);
size = kcov->size * sizeof(unsigned long);
- if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
+ if (kcov->area == NULL || 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_irqrestore(&kcov->lock, flags);
- 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;
+ spin_unlock_irqrestore(&kcov->lock, flags);
+ vma->vm_flags |= VM_DONTEXPAND;
+ 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_irqrestore(&kcov->lock, flags);
- vfree(area);
return res;
}

@@ -674,6 +665,7 @@ static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
unsigned int remote_num_handles;
unsigned long remote_arg_size;
unsigned long size, flags;
+ void *area;

kcov = filep->private_data;
switch (cmd) {
@@ -683,17 +675,21 @@ static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
* Must happen before anything else.
*
* First check the size argument - it must be at least 2
- * to hold the current position and one PC. Later we allocate
- * size * sizeof(unsigned long) memory, that must not overflow.
+ * to hold the current position and one PC.
*/
size = arg;
if (size < 2 || size > INT_MAX / sizeof(unsigned long))
return -EINVAL;
+ area = vmalloc_user(size * sizeof(unsigned long));
+ if (area == NULL)
+ return -ENOMEM;
spin_lock_irqsave(&kcov->lock, flags);
if (kcov->mode != KCOV_MODE_DISABLED) {
spin_unlock_irqrestore(&kcov->lock, flags);
+ vfree(area);
return -EBUSY;
}
+ kcov->area = area;
kcov->size = size;
kcov->mode = KCOV_MODE_INIT;
spin_unlock_irqrestore(&kcov->lock, flags);
--
2.34.1.703.g22d0c6ccf7-goog
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