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authorChristian Borntraeger <borntraeger@linux.ibm.com>2023-05-15 10:42:34 +0200
committerJanosch Frank <frankja@linux.ibm.com>2023-06-16 11:08:09 +0200
commit0bc380beb78aa352eadbc21d934dd9606fcee808 (patch)
tree77feadb3b7dd8ca8d224623b2d19900441df2adc
parent246be7d2720ea9a795b576067ecc5e5c7a1e7848 (diff)
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: 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> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
-rw-r--r--arch/s390/kvm/diag.c8
1 files 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);