linux-kernel - [PATCH 4.19 21/50] KVM: s390: kvm_s390_vm_start_migration: check dirty_bitmap before using it as target for memset()

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Message-Id: <20190918061225.325572504@linuxfoundation.org>
Date:   Wed, 18 Sep 2019 08:19:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Igor Mammedov <imammedo@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Janosch Frank <frankja@...ux.ibm.com>
Subject: [PATCH 4.19 21/50] KVM: s390: kvm_s390_vm_start_migration: check dirty_bitmap before using it as target for memset()

From: Igor Mammedov <imammedo@...hat.com>

commit 13a17cc0526f08d1df9507f7484176371cd263a0 upstream.

If userspace doesn't set KVM_MEM_LOG_DIRTY_PAGES on memslot before calling
kvm_s390_vm_start_migration(), kernel will oops with:

  Unable to handle kernel pointer dereference in virtual kernel address space
  Failing address: 0000000000000000 TEID: 0000000000000483
  Fault in home space mode while using kernel ASCE.
  AS:0000000002a2000b R2:00000001bff8c00b R3:00000001bff88007 S:00000001bff91000 P:000000000000003d
  Oops: 0004 ilc:2 [#1] SMP
  ...
  Call Trace:
  ([<001fffff804ec552>] kvm_s390_vm_set_attr+0x347a/0x3828 [kvm])
   [<001fffff804ecfc0>] kvm_arch_vm_ioctl+0x6c0/0x1998 [kvm]
   [<001fffff804b67e4>] kvm_vm_ioctl+0x51c/0x11a8 [kvm]
   [<00000000008ba572>] do_vfs_ioctl+0x1d2/0xe58
   [<00000000008bb284>] ksys_ioctl+0x8c/0xb8
   [<00000000008bb2e2>] sys_ioctl+0x32/0x40
   [<000000000175552c>] system_call+0x2b8/0x2d8
  INFO: lockdep is turned off.
  Last Breaking-Event-Address:
   [<0000000000dbaf60>] __memset+0xc/0xa0

due to ms->dirty_bitmap being NULL, which might crash the host.

Make sure that ms->dirty_bitmap is set before using it or
return -EINVAL otherwise.

Cc: <stable@...r.kernel.org>
Fixes: afdad61615cc ("KVM: s390: Fix storage attributes migration with memory slots")
Signed-off-by: Igor Mammedov <imammedo@...hat.com>
Link: https://lore.kernel.org/kvm/20190911075218.29153-1-imammedo@redhat.com/
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@...hat.com>
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>
Signed-off-by: Janosch Frank <frankja@...ux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/s390/kvm/kvm-s390.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -928,6 +928,8 @@ static int kvm_s390_vm_start_migration(s
 	/* mark all the pages in active slots as dirty */
 	for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
 		ms = slots->memslots + slotnr;
+		if (!ms->dirty_bitmap)
+			return -EINVAL;
 		/*
 		 * The second half of the bitmap is only used on x86,
 		 * and would be wasted otherwise, so we put it to good