linux-kernel - [PATCH 4.9 002/138] s390/runtime instrumention: fix possible memory corruption

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20171128100544.966299521@linuxfoundation.org>
Date:   Tue, 28 Nov 2017 11:21:43 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: [PATCH 4.9 002/138] s390/runtime instrumention: fix possible memory corruption

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Heiko Carstens <heiko.carstens@...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@...ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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;
 	}