Patch "s390/ptrace: fix guarded storage regset handling" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

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

    s390/ptrace: fix guarded storage regset handling

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-ptrace-fix-guarded-storage-regset-handling.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 foo@baz Wed Dec  6 18:04:41 CET 2017
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Mon, 11 Sep 2017 11:24:23 +0200
Subject: s390/ptrace: fix guarded storage regset handling

From: Heiko Carstens <heiko.carstens@de.ibm.com>


[ Upstream commit 5ef2d5231d547c672c67bdf84c13a4adaf477964 ]

If the guarded storage regset for current is supposed to be changed,
the regset from user space is copied directly into the guarded storage
control block.

If then the process gets scheduled away while the control block is
being copied and before the new control block has been loaded, the
result is random: the process can be scheduled away due to a page
fault or preemption. If that happens the already copied parts will be
overwritten by save_gs_cb(), called from switch_to().

Avoid this by copying the data to a temporary buffer on the stack and
do the actual update with preemption disabled.

Fixes: f5bbd7219891 ("s390/ptrace: guarded storage regset for the current task")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/kernel/ptrace.c |   33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -1172,26 +1172,37 @@ static int s390_gs_cb_set(struct task_st
 			  unsigned int pos, unsigned int count,
 			  const void *kbuf, const void __user *ubuf)
 {
-	struct gs_cb *data = target->thread.gs_cb;
+	struct gs_cb gs_cb = { }, *data = NULL;
 	int rc;
 
 	if (!MACHINE_HAS_GS)
 		return -ENODEV;
-	if (!data) {
+	if (!target->thread.gs_cb) {
 		data = kzalloc(sizeof(*data), GFP_KERNEL);
 		if (!data)
 			return -ENOMEM;
-		data->gsd = 25;
-		target->thread.gs_cb = data;
-		if (target == current)
-			__ctl_set_bit(2, 4);
-	} else if (target == current) {
-		save_gs_cb(data);
 	}
+	if (!target->thread.gs_cb)
+		gs_cb.gsd = 25;
+	else if (target == current)
+		save_gs_cb(&gs_cb);
+	else
+		gs_cb = *target->thread.gs_cb;
 	rc = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
-				data, 0, sizeof(struct gs_cb));
-	if (target == current)
-		restore_gs_cb(data);
+				&gs_cb, 0, sizeof(gs_cb));
+	if (rc) {
+		kfree(data);
+		return -EFAULT;
+	}
+	preempt_disable();
+	if (!target->thread.gs_cb)
+		target->thread.gs_cb = data;
+	*target->thread.gs_cb = gs_cb;
+	if (target == current) {
+		__ctl_set_bit(2, 4);
+		restore_gs_cb(target->thread.gs_cb);
+	}
+	preempt_enable();
 	return rc;
 }
 


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

queue-4.14/s390-ptrace-fix-guarded-storage-regset-handling.patch
queue-4.14/s390-pci-do-not-require-ais-facility.patch
queue-4.14/perf-test-attr-fix-ignored-test-case-result.patch
queue-4.14/s390-runtime-instrumentation-simplify-task-exit-handling.patch
queue-4.14/perf-test-attr-fix-python-error-on-empty-result.patch