| Message ID | 20230523140500.271990-1-borntraeger@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390/diag: fix racy access of physical cpu number in diag 9c handler | expand |
On 23.05.23 16:05, Christian Borntraeger wrote: > We do check for target CPU == -1, but this might change at the time we > are going to use it. Hold the physical target CPU in a local variable to > avoid out-of-bound accesses to the cpu arrays. > > Cc: Pierre Morel <pmorel@linux.ibm.com> > Fixes: 87e28a15c42c ("KVM: s390: diag9c (directed yield) forwarding") > Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com> > Reviewed-by: Nico Boehr <nrb@linux.ibm.com> > Reviewed-by: Pierre Morel <pmorel@linux.ibm.com> > Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com> > --- > arch/s390/kvm/diag.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c > index 807fa9da1e72..3c65b8258ae6 100644 > --- a/arch/s390/kvm/diag.c > +++ b/arch/s390/kvm/diag.c > @@ -166,6 +166,7 @@ static int diag9c_forwarding_overrun(void) > static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) > { > struct kvm_vcpu *tcpu; > + int tcpu_cpu; > int tid; > > tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4]; > @@ -181,14 +182,15 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) > goto no_yield; > > /* target guest VCPU already running */ > - if (READ_ONCE(tcpu->cpu) >= 0) { > + tcpu_cpu = READ_ONCE(tcpu->cpu); > + if (tcpu_cpu >= 0) { > if (!diag9c_forwarding_hz || diag9c_forwarding_overrun()) > goto no_yield; > > /* target host CPU already running */ > - if (!vcpu_is_preempted(tcpu->cpu)) > + if (!vcpu_is_preempted(tcpu_cpu)) > goto no_yield; > - smp_yield_cpu(tcpu->cpu); > + smp_yield_cpu(tcpu_cpu); > VCPU_EVENT(vcpu, 5, > "diag time slice end directed to %d: yield forwarded", > tid); Reviewed-by: David Hildenbrand <david@redhat.com>
On Tue, 23 May 2023 16:05:00 +0200 Christian Borntraeger <borntraeger@linux.ibm.com> wrote: > We do check for target CPU == -1, but this might change at the time we > are going to use it. Hold the physical target CPU in a local variable to > avoid out-of-bound accesses to the cpu arrays. > > Cc: Pierre Morel <pmorel@linux.ibm.com> > Fixes: 87e28a15c42c ("KVM: s390: diag9c (directed yield) forwarding") > Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com> > Reviewed-by: Nico Boehr <nrb@linux.ibm.com> > Reviewed-by: Pierre Morel <pmorel@linux.ibm.com> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com> > --- > arch/s390/kvm/diag.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c > index 807fa9da1e72..3c65b8258ae6 100644 > --- a/arch/s390/kvm/diag.c > +++ b/arch/s390/kvm/diag.c > @@ -166,6 +166,7 @@ static int diag9c_forwarding_overrun(void) > static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) > { > struct kvm_vcpu *tcpu; > + int tcpu_cpu; > int tid; > > tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4]; > @@ -181,14 +182,15 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) > goto no_yield; > > /* target guest VCPU already running */ > - if (READ_ONCE(tcpu->cpu) >= 0) { > + tcpu_cpu = READ_ONCE(tcpu->cpu); > + if (tcpu_cpu >= 0) { > if (!diag9c_forwarding_hz || diag9c_forwarding_overrun()) > goto no_yield; > > /* target host CPU already running */ > - if (!vcpu_is_preempted(tcpu->cpu)) > + if (!vcpu_is_preempted(tcpu_cpu)) > goto no_yield; > - smp_yield_cpu(tcpu->cpu); > + smp_yield_cpu(tcpu_cpu); > VCPU_EVENT(vcpu, 5, > "diag time slice end directed to %d: yield forwarded", > tid);
diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c index 807fa9da1e72..3c65b8258ae6 100644 --- a/arch/s390/kvm/diag.c +++ b/arch/s390/kvm/diag.c @@ -166,6 +166,7 @@ static int diag9c_forwarding_overrun(void) static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) { struct kvm_vcpu *tcpu; + int tcpu_cpu; int tid; tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4]; @@ -181,14 +182,15 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) goto no_yield; /* target guest VCPU already running */ - if (READ_ONCE(tcpu->cpu) >= 0) { + tcpu_cpu = READ_ONCE(tcpu->cpu); + if (tcpu_cpu >= 0) { if (!diag9c_forwarding_hz || diag9c_forwarding_overrun()) goto no_yield; /* target host CPU already running */ - if (!vcpu_is_preempted(tcpu->cpu)) + if (!vcpu_is_preempted(tcpu_cpu)) goto no_yield; - smp_yield_cpu(tcpu->cpu); + smp_yield_cpu(tcpu_cpu); VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: yield forwarded", tid);
We do check for target CPU == -1, but this might change at the time we are going to use it. Hold the physical target CPU in a local variable to avoid out-of-bound accesses to the cpu arrays. Cc: Pierre Morel <pmorel@linux.ibm.com> Fixes: 87e28a15c42c ("KVM: s390: diag9c (directed yield) forwarding") Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com> Reviewed-by: Nico Boehr <nrb@linux.ibm.com> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com> --- arch/s390/kvm/diag.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)