Am 23.03.22 um 09:57 schrieb Janosch Frank:
On 3/23/22 09:52, Janis Schoetterl-Glausch wrote:
On 3/23/22 08:58, Janosch Frank wrote:
On 3/22/22 16:32, Janis Schoetterl-Glausch wrote:
Issuing a memop on a protected vm does not make sense,
Issuing a vm memop on a protected vm...
The cpu memop still makes sense, no?
The vcpu memop does hold the vcpu->lock, so no lockdep issue.
If you issue a vcpu memop while enabling protected virtualization,
the memop might find that the vcpu is not protected, while other vcpus
might already be, but I don't think there's a way to create secure memory
concurrent with the memop.
I just wanted you to make this a bit more specific since we now have vm and vcpu memops. vm memops don't make sense for pv guests but vcpu ones are needed to access the sida.
Right, I think changing the commit messages
- Issuing a memop on a protected vm does not make sense
+ Issuing a vm memop on a protected vm does not make sense
does make sense.
neither is the memory readable/writable, nor does it make sense to check
storage keys. This is why the ioctl will return -EINVAL when it detects
the vm to be protected. However, in order to ensure that the vm cannot
become protected during the memop, the kvm->lock would need to be taken
for the duration of the ioctl. This is also required because
kvm_s390_pv_is_protected asserts that the lock must be held.
Instead, don't try to prevent this. If user space enables secure
execution concurrently with a memop it must accecpt the possibility of
the memop failing.
Still check if the vm is currently protected, but without locking and
consider it a heuristic.
Fixes: ef11c9463ae0 ("KVM: s390: Add vm IOCTL for key checked guest absolute memory access")
Signed-off-by: Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx>
Makes sense to me.
Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
---
arch/s390/kvm/kvm-s390.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ca96f84db2cc..53adbe86a68f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2385,7 +2385,16 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
return -EINVAL;
if (mop->size > MEM_OP_MAX_SIZE)
return -E2BIG;
- if (kvm_s390_pv_is_protected(kvm))
+ /*
+ * This is technically a heuristic only, if the kvm->lock is not
+ * taken, it is not guaranteed that the vm is/remains non-protected.
+ * This is ok from a kernel perspective, wrongdoing is detected
+ * on the access, -EFAULT is returned and the vm may crash the
+ * next time it accesses the memory in question.
+ * There is no sane usecase to do switching and a memop on two
+ * different CPUs at the same time.
+ */
+ if (kvm_s390_pv_get_handle(kvm))
return -EINVAL;
if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
if (access_key_invalid(mop->key))
base-commit: c9b8fecddb5bb4b67e351bbaeaa648a6f7456912
