| From | Luis Henriques <> | Subject | [PATCH 3.16.y-ckt 045/126] KVM: s390: SCA must not cross page boundaries | Date | Wed, 9 Dec 2015 09:36:55 +0000 |
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3.16.7-ckt21 -stable review patch. If anyone has any objections, please let me know.
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From: David Hildenbrand <dahi@linux.vnet.ibm.com>
commit c5c2c393468576bad6d10b2b5fefff8cd25df3f4 upstream.
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.
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> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- arch/s390/kvm/kvm-s390.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 5e9217d96cfe..fd8a8373c275 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -429,7 +429,9 @@ 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);
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