From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Thu, 3 Aug 2017 13:05:40 +0200
Subject: KVM: s390: sthyi: remove invalid guest write access
Patch-mainline: v4.14-rc1
Git-commit: 631aebfee8261d66597ce0f88ba046c77a0e415e
References: bsc#1077761
handle_sthyi() always writes to guest memory if the sthyi function
code is zero in order to fault in the page that later is written to.
However a function code of zero does not necessarily mean that a write
to guest memory happens: if the KVM host is running as a second level
guest under z/VM 6.2 the sthyi instruction is indicated to be
available to the KVM host, however if the instruction is executed it
will always return with a return code that indicates "unsupported
function code".
In such a case handle_sthyi() must not write to guest memory. This
means that the prior write access to fault in the guest page may
result in invalid guest exceptions, and/or invalid data modification.
In order to be architecture compliant simply remove the write_guest()
call.
Given that the guest assumed a write access anyway, this fix does not
qualify for -stable. This just makes sure the sthyi handler is
architecture compliant.
Fixes: 95ca2cb57985 ("KVM: s390: Add sthyi emulation")
Reviewed-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Alexander Graf <agraf@suse.de>
---
arch/s390/kvm/sthyi.c | 8 --------
1 file changed, 8 deletions(-)
--- a/arch/s390/kvm/sthyi.c
+++ b/arch/s390/kvm/sthyi.c
@@ -436,14 +436,6 @@
if (addr & ~PAGE_MASK)
return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
- /*
- * If the page has not yet been faulted in, we want to do that
- * now and not after all the expensive calculations.
- */
- r = write_guest(vcpu, addr, reg2, &cc, 1);
- if (r)
- return kvm_s390_inject_prog_cond(vcpu, r);
-
sctns = (void *)get_zeroed_page(GFP_KERNEL);
if (!sctns)
return -ENOMEM;