KVM: s390: sthyi: remove invalid guest write access

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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: 95ca2cb579 ("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>

...

This commit is contained in:

Heiko Carstens 2017-08-03 13:05:40 +02:00 • committed by Christian Borntraeger

parent 8fa1696ea7

commit 631aebfee8

1 changed files with 0 additions and 8 deletions

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arch/s390/kvm/sthyi.c

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