Patch "s390/guarded storage: fix possible memory corruption" has been added to the 4.14-stable tree

Patch "s390/guarded storage: fix possible memory corruption" has been added to the 4.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    s390/guarded storage: fix possible memory corruption

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     s390-guarded-storage-fix-possible-memory-corruption.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From fa1edf3f63c05ca8eacafcd7048ed91e5360f1a8 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Mon, 11 Sep 2017 11:24:22 +0200
Subject: s390/guarded storage: fix possible memory corruption

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)


Patches currently in stable-queue which might be from heiko.carstens@de.ibm.com are

queue-4.14/s390-guarded-storage-fix-possible-memory-corruption.patch
queue-4.14/s390-disassembler-add-missing-end-marker-for-e7-table.patch
queue-4.14/s390-fix-transactional-execution-control-register-handling.patch
queue-4.14/s390-runtime-instrumention-fix-possible-memory-corruption.patch
queue-4.14/s390-noexec-execute-kexec-datamover-without-dat.patch