| Message ID | 20200403153050.20569-3-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: vsie: fixes and cleanups | expand |
On Fri, 3 Apr 2020 17:30:47 +0200 David Hildenbrand <david@redhat.com> wrote: > Whenever we get an -EFAULT, we failed to read in guest 2 physical > address space. Such addressing exceptions are reported via a program > intercept to the nested hypervisor. > > We faked the intercept, we have to return to guest 2. Instead, right > now we would be returning -EFAULT from the intercept handler, > eventually crashing the VM. > > Addressing exceptions can only happen if the g2->g3 page tables > reference invalid g2 addresses (say, either a table or the final page > is not accessible - so something that basically never happens in sane > environments. > > Identified by manual code inspection. > > Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested > virtualization") Cc: <stable@vger.kernel.org> # v4.8+ > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > arch/s390/kvm/vsie.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c > index 076090f9e666..4f6c22d72072 100644 > --- a/arch/s390/kvm/vsie.c > +++ b/arch/s390/kvm/vsie.c > @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, > struct vsie_page *vsie_page) scb_s->iprcc = PGM_ADDRESSING; > scb_s->pgmilc = 4; > scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); > + rc = 1; > } > return rc; > } so, the reason why we never noticed this issue before is simply that nobody tried running a misbehaving nested guest? Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
On 07.04.20 13:00, Claudio Imbrenda wrote: > On Fri, 3 Apr 2020 17:30:47 +0200 > David Hildenbrand <david@redhat.com> wrote: > >> Whenever we get an -EFAULT, we failed to read in guest 2 physical >> address space. Such addressing exceptions are reported via a program >> intercept to the nested hypervisor. >> >> We faked the intercept, we have to return to guest 2. Instead, right >> now we would be returning -EFAULT from the intercept handler, >> eventually crashing the VM. >> >> Addressing exceptions can only happen if the g2->g3 page tables >> reference invalid g2 addresses (say, either a table or the final page >> is not accessible - so something that basically never happens in sane >> environments. >> >> Identified by manual code inspection. >> >> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested >> virtualization") Cc: <stable@vger.kernel.org> # v4.8+ >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> arch/s390/kvm/vsie.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >> index 076090f9e666..4f6c22d72072 100644 >> --- a/arch/s390/kvm/vsie.c >> +++ b/arch/s390/kvm/vsie.c >> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, >> struct vsie_page *vsie_page) scb_s->iprcc = PGM_ADDRESSING; >> scb_s->pgmilc = 4; >> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); >> + rc = 1; >> } >> return rc; >> } > > so, the reason why we never noticed this issue before is simply that > nobody tried running a misbehaving nested guest? Yes, actually, a misbehaving nested hypervisor. > > Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > Thanks!
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c index 076090f9e666..4f6c22d72072 100644 --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) scb_s->iprcc = PGM_ADDRESSING; scb_s->pgmilc = 4; scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); + rc = 1; } return rc; }
Whenever we get an -EFAULT, we failed to read in guest 2 physical address space. Such addressing exceptions are reported via a program intercept to the nested hypervisor. We faked the intercept, we have to return to guest 2. Instead, right now we would be returning -EFAULT from the intercept handler, eventually crashing the VM. Addressing exceptions can only happen if the g2->g3 page tables reference invalid g2 addresses (say, either a table or the final page is not accessible - so something that basically never happens in sane environments. Identified by manual code inspection. Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") Cc: <stable@vger.kernel.org> # v4.8+ Signed-off-by: David Hildenbrand <david@redhat.com> --- arch/s390/kvm/vsie.c | 1 + 1 file changed, 1 insertion(+)