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Subject[PATCH 1/2] kcov: size of arena is now given in bytes.
Date
We'll introduce a different mode of tracing a-la AFL fixed table and Dmitry
suggests that the code would be simpler with the size expressed in bytes as
opposed unsigned longs.

We only change the kcov::size field, which will be shared between different
modes, but leave the task_struct::kcov_size field expressed in unsigned
long in order to save an unecessary bitshift/division in the hot path when
using KCOV_MODE_TRACE.

Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Michal Zalewski <lcamtuf@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
---
kernel/kcov.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 30e6d05aa5a9..c2aa93851f93 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -32,7 +32,7 @@ struct kcov {
/* 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). */
+ /* Size of arena in bytes. */
unsigned size;
/* Coverage buffer shared with user space. */
void *area;
@@ -140,7 +140,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
return -ENOMEM;

spin_lock(&kcov->lock);
- size = kcov->size * sizeof(unsigned long);
+ size = kcov->size;
if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
vma->vm_end - vma->vm_start != size) {
res = -EINVAL;
@@ -198,13 +198,11 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
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->size = size * sizeof(unsigned long);
kcov->mode = KCOV_MODE_TRACE;
return 0;
case KCOV_ENABLE:
@@ -223,7 +221,7 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
return -EBUSY;
t = current;
/* Cache in task struct for performance. */
- t->kcov_size = kcov->size;
+ t->kcov_size = kcov->size / sizeof(unsigned long);
t->kcov_area = kcov->area;
/* See comment in __sanitizer_cov_trace_pc(). */
barrier();
--
2.10.2
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