From d6e646ad7cfa7034d280459b2b2546288f247144 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Mon, 11 Sep 2017 11:24:22 +0200 Subject: [PATCH] s390/runtime instrumention: fix possible memory corruption 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") Cc: # v3.7+ Reviewed-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/runtime_instr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/s390/kernel/runtime_instr.c b/arch/s390/kernel/runtime_instr.c index 429d3a782f1c..b9738ae2e1de 100644 --- a/arch/s390/kernel/runtime_instr.c +++ b/arch/s390/kernel/runtime_instr.c @@ -49,11 +49,13 @@ 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) @@ -64,9 +66,7 @@ SYSCALL_DEFINE1(s390_runtime_instr, int, command) return -EOPNOTSUPP; if (command == S390_RUNTIME_INSTR_STOP) { - preempt_disable(); exit_thread_runtime_instr(); - preempt_enable(); return 0; }