4.14-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 fa1edf3f63c05ca8eacafcd7048ed91e5360f1a8 upstream.
For PREEMPT enabled kernels the guarded storage (GS) code contains a possible use-after-free bug. If a task that makes use of GS 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_gs() gets preempted after the GS control block of the task has been freed but before the pointer to it is set to NULL, then save_gs_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: 916cda1aa1b4 ("s390: add a system call for guarded storage") 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/guarded_storage.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/s390/kernel/guarded_storage.c +++ b/arch/s390/kernel/guarded_storage.c @@ -14,9 +14,11 @@
void exit_thread_gs(void) { + preempt_disable(); kfree(current->thread.gs_cb); kfree(current->thread.gs_bc_cb); current->thread.gs_cb = current->thread.gs_bc_cb = NULL; + preempt_enable(); }
static int gs_enable(void)