4.4-stable review patch. If anyone has any objections, please let me know.
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From: Heiko Carstens heiko.carstens@de.ibm.com
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@de.ibm.com Signed-off-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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 @@ -47,11 +47,13 @@ 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_cb = NULL; + preempt_enable(); }
SYSCALL_DEFINE1(s390_runtime_instr, int, command) @@ -62,9 +64,7 @@ SYSCALL_DEFINE1(s390_runtime_instr, int, return -EOPNOTSUPP;
if (command == S390_RUNTIME_INSTR_STOP) { - preempt_disable(); exit_thread_runtime_instr(); - preempt_enable(); return 0; }