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Commit fa1edf3f authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
Browse files

s390/guarded storage: fix possible memory corruption 



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: 916cda1a ("s390: add a system call for guarded storage")
Cc: <stable@vger.kernel.org> # v4.12+
Reviewed-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 8d9047f8

arch/s390/kernel/guarded_storage.c

+2 −0
Original line number Diff line number Diff line
@@ -13,9 +13,11 @@ 


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)