Patch "s390/mm: fix BUG_ON in crst_table_upgrade" has been added to the 4.12-stable tree

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

s390/mm: fix BUG_ON in crst_table_upgrade

to the 4.12-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-mm-fix-bug_on-in-crst_table_upgrade.patch

and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Martin Schwidefsky <[email protected]>
Date: Thu, 31 Aug 2017 13:18:22 +0200
Subject: s390/mm: fix BUG_ON in crst_table_upgrade

From: Martin Schwidefsky <[email protected]>

commit 8ab867cb0806a8e195de161fd8883a0578d1d050 upstream.

A 31-bit compat process can force a BUG_ON in crst_table_upgrade with specific, invalid mmap calls, e.g.

mmap((void*) 0x7fff8000, 0x10000, 3, 32, -1, 0)

The arch_get_unmapped_area[_topdown] functions miss an if condition in the decision to do a page table upgrade.

[ms: Backport to 4.12, minor context change]

---
 arch/s390/mm/mmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -119,7 +119,8 @@ arch_get_unmapped_area(struct file *filp
 		return addr;
 
 check_asce_limit:
-	if (addr + len > current->mm->context.asce_limit) {
+	if (addr + len > current->mm->context.asce_limit &&
+	    addr + len <= TASK_SIZE) {
 		rc = crst_table_upgrade(mm);
 		if (rc)
 			return (unsigned long) rc;

@@ -183,7 +184,8 @@ arch_get_unmapped_area_topdown(struct fi
 	}
 
 check_asce_limit:
-	if (addr + len > current->mm->context.asce_limit) {
+	if (addr + len > current->mm->context.asce_limit &&
+	    addr + len <= TASK_SIZE) {
 		rc = crst_table_upgrade(mm);
 		if (rc)
 			return (unsigned long) rc;

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/s390-mm-avoid-empty-zero-pages-for-kvm-guests-to-avoid-postcopy-hangs.patch queue-4.12/s390-mm-fix-bug_on-in-crst_table_upgrade.patch