3.16.54-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
commit d6e646ad7cfa7034d280459b2b2546288f247144 upstream.
For PREEMPT enabled kernels the runtime instrumentation (RI) code
contains a possible use-after-free bug. If a task that makes use of RI
exits, it will execute do_exit() while still enabled for preemption.
That function will call exit_thread_runtime_instr() via
exit_thread(). If exit_thread_runtime_instr() gets preempted after the
RI control block of the task has been freed but before the pointer to
it is set to NULL, then save_ri_cb(), called from switch_to(), will
write to already freed memory.
Avoid this and simply disable preemption while freeing the control
block and setting the pointer to NULL.
Fixes: e4b8b3f33fca ("s390: add support for runtime instrumentation")
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/s390/kernel/runtime_instr.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/s390/kernel/runtime_instr.c
+++ b/arch/s390/kernel/runtime_instr.c
@@ -53,12 +53,14 @@ void exit_thread_runtime_instr(void)
{
struct task_struct *task = current;
+ preempt_disable();
if (!task->thread.ri_cb)
return;
disable_runtime_instr();
kfree(task->thread.ri_cb);
task->thread.ri_signum = 0;
task->thread.ri_cb = NULL;
+ preempt_enable();
}
static void runtime_instr_int_handler(struct ext_code ext_code,
@@ -100,9 +102,7 @@ SYSCALL_DEFINE2(s390_runtime_instr, int,
return -EOPNOTSUPP;
if (command == S390_RUNTIME_INSTR_STOP) {
- preempt_disable();
exit_thread_runtime_instr();
- preempt_enable();
return 0;
}