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KVM: s390/diag: fix racy access of physical cpu number in diag 9c handler 

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: 87e28a15c4 ("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>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Christian Borntraeger 2023-05-15 10:42:34 +02:00 committed by Janosch Frank
parent 246be7d272
commit 0bc380beb7
1 changed files with 5 additions and 3 deletions
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8
arch/s390/kvm/diag.c
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@ -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);