From 631aebfee8261d66597ce0f88ba046c77a0e415e Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Thu, 3 Aug 2017 13:05:40 +0200 Subject: [PATCH] KVM: s390: sthyi: remove invalid guest write access 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 Signed-off-by: Heiko Carstens Reviewed-by: Cornelia Huck Signed-off-by: Christian Borntraeger --- arch/s390/kvm/sthyi.c | 8 -------- 1 file changed, 8 deletions(-) diff --git a/arch/s390/kvm/sthyi.c b/arch/s390/kvm/sthyi.c index a2e5c24f47a7..395926b8c1ed 100644 --- a/arch/s390/kvm/sthyi.c +++ b/arch/s390/kvm/sthyi.c @@ -436,14 +436,6 @@ int handle_sthyi(struct kvm_vcpu *vcpu) 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;