[lkml]   [2018]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 1/3] kcov: ensure irq code sees a valid area
For kernels built with CONFIG_PREEMPT, some C code may execute before or
after the interrupt handler, while the hardirq count is zero. In these
cases, in_task() can return true.

A task can be interrupted in the middle of a KCOV_DISABLE ioctl while it
resets the task's kcov data via kcov_task_init(). Instrumented code
executed during this period will call __sanitizer_cov_trace_pc(), and as
in_task() returns true, will inspect t->kcov_mode before trying to write
to t->kcov_area.

In kcov_init_task() Since we update t->kcov_{mode,area,size} with plain
stores, which may be re-ordered, torn, etc. Thus
__sanitizer_cov_trace_pc() may see bogus values for any of these fields,
and may attempt to write to memory which is not mapped.

Let's avoid this by using WRITE_ONCE() to set t->kcov_mode, with a
barrier() to ensure this is ordered before we clear t->kov_{area,size}.
This ensures that any code execute while kcov_init_task() is preempted
will either see valid values for t->kcov_{area,size}, or will see that
t->kcov_mode is KCOV_MODE_DISABLED, and bail out without touching

Signed-off-by: Mark Rutland <>
Cc: Andrew Morton <>
Cc: Andrey Ryabinin <>
Cc: Dmitry Vyukov <>
kernel/kcov.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 2c16f1ab5e10..5be9a60a959f 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -241,7 +241,8 @@ static void kcov_put(struct kcov *kcov)

void kcov_task_init(struct task_struct *t)
- t->kcov_mode = KCOV_MODE_DISABLED;
+ barrier();
t->kcov_size = 0;
t->kcov_area = NULL;
t->kcov = NULL;
 \ /
  Last update: 2018-05-04 15:56    [W:0.060 / U:7.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site