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authorDavid Hildenbrand2015-10-26 08:41:29 +0100
committerChristian Borntraeger2015-10-29 15:58:41 +0100
commitc5c2c393468576bad6d10b2b5fefff8cd25df3f4 (patch)
treeb4e09d33d0adfc57d9b752dde228529c368113f6 /arch/s390/kvm/kvm-s390.c
parentKVM: s390: factor out reading of the guest TOD clock (diff)
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KVM: s390: SCA must not cross page boundaries
We seemed to have missed a few corner cases in commit f6c137ff00a4 ("KVM: s390: randomize sca address"). The SCA has a maximum size of 2112 bytes. By setting the sca_offset to some unlucky numbers, we exceed the page. 0x7c0 (1984) -> Fits exactly 0x7d0 (2000) -> 16 bytes out 0x7e0 (2016) -> 32 bytes out 0x7f0 (2032) -> 48 bytes out One VCPU entry is 32 bytes long. For the last two cases, we actually write data to the other page. 1. The address of the VCPU. 2. Injection/delivery/clearing of SIGP externall calls via SIGP IF. Especially the 2. happens regularly. So this could produce two problems: 1. The guest losing/getting external calls. 2. Random memory overwrites in the host. So this problem happens on every 127 + 128 created VM with 64 VCPUs. Cc: stable@vger.kernel.org # v3.15+ Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Diffstat (limited to 'arch/s390/kvm/kvm-s390.c')
-rw-r--r--arch/s390/kvm/kvm-s390.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 618c85411a51..35596177fad2 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1098,7 +1098,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
if (!kvm->arch.sca)
goto out_err;
spin_lock(&kvm_lock);
- sca_offset = (sca_offset + 16) & 0x7f0;
+ sca_offset += 16;
+ if (sca_offset + sizeof(struct sca_block) > PAGE_SIZE)
+ sca_offset = 0;
kvm->arch.sca = (struct sca_block *) ((char *) kvm->arch.sca + sca_offset);
spin_unlock(&kvm_lock);