Commit 7c724edb authored by David Hildenbrand's avatar David Hildenbrand Committed by Luis Henriques

KVM: s390: SCA must not cross page boundaries

commit c5c2c393 upstream.

We seemed to have missed a few corner cases in commit f6c137ff
("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: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent dea853b1
...@@ -429,7 +429,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) ...@@ -429,7 +429,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
if (!kvm->arch.sca) if (!kvm->arch.sca)
goto out_err; goto out_err;
spin_lock(&kvm_lock); 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); kvm->arch.sca = (struct sca_block *) ((char *) kvm->arch.sca + sca_offset);
spin_unlock(&kvm_lock); spin_unlock(&kvm_lock);
......
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