| Message ID | 20180504135535.53744-2-mark.rutland@arm.com |
|---|---|
| State | Accepted |
| Commit | c9484b986ef03492357fddd50afbdd02929cfa72 |
| Headers | show |
| Series | kcov: fix unexpected faults | expand |
On Fri, May 04, 2018 at 02:55:33PM +0100, Mark Rutland wrote: > 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. Whoops; that 'Since' shuoldn't be there. I've fixed this up locally. Mark.
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; + WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED); + barrier(); t->kcov_size = 0; t->kcov_area = NULL; t->kcov = NULL;
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 t->kcov_area. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Dmitry Vyukov <dvyukov@google.com> --- kernel/kcov.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) -- 2.11.0