KVM: s390: Add vm IOCTL for key checked guest absolute memory access

Channel I/O honors storage keys and is performed on absolute memory.
For I/O emulation user space therefore needs to be able to do key
checked accesses.
The vm IOCTL supports read/write accesses, as well as checking
if an access would succeed.
Unlike relying on KVM_S390_GET_SKEYS for key checking would,
the vm IOCTL performs the check in lockstep with the read or write,
by, ultimately, mapping the access to move instructions that
support key protection checking with a supplied key.
Fetch and storage protection override are not applicable to absolute
accesses and so are not applied as they are when using the vcpu memop.

Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20220211182215.2730017-7-scgl@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>

1 files changed, 81 insertions, 0 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c31b40abfa23..36bc73b5f5de 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2364,6 +2364,78 @@ static bool access_key_invalid(u8 access_key)
 	return access_key > 0xf;
 }
 
+static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
+{
+	void __user *uaddr = (void __user *)mop->buf;
+	u64 supported_flags;
+	void *tmpbuf = NULL;
+	int r, srcu_idx;
+
+	supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION
+			  | KVM_S390_MEMOP_F_CHECK_ONLY;
+	if (mop->flags & ~supported_flags)
+		return -EINVAL;
+	if (mop->size > MEM_OP_MAX_SIZE)
+		return -E2BIG;
+	if (kvm_s390_pv_is_protected(kvm))
+		return -EINVAL;
+	if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
+		if (access_key_invalid(mop->key))
+			return -EINVAL;
+	} else {
+		mop->key = 0;
+	}
+	if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
+		tmpbuf = vmalloc(mop->size);
+		if (!tmpbuf)
+			return -ENOMEM;
+	}
+
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+
+	if (kvm_is_error_gpa(kvm, mop->gaddr)) {
+		r = PGM_ADDRESSING;
+		goto out_unlock;
+	}
+
+	switch (mop->op) {
+	case KVM_S390_MEMOP_ABSOLUTE_READ: {
+		if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
+			r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_FETCH, mop->key);
+		} else {
+			r = access_guest_abs_with_key(kvm, mop->gaddr, tmpbuf,
+						      mop->size, GACC_FETCH, mop->key);
+			if (r == 0) {
+				if (copy_to_user(uaddr, tmpbuf, mop->size))
+					r = -EFAULT;
+			}
+		}
+		break;
+	}
+	case KVM_S390_MEMOP_ABSOLUTE_WRITE: {
+		if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
+			r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key);
+		} else {
+			if (copy_from_user(tmpbuf, uaddr, mop->size)) {
+				r = -EFAULT;
+				break;
+			}
+			r = access_guest_abs_with_key(kvm, mop->gaddr, tmpbuf,
+						      mop->size, GACC_STORE, mop->key);
+		}
+		break;
+	}
+	default:
+		r = -EINVAL;
+	}
+
+out_unlock:
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+	vfree(tmpbuf);
+	return r;
+}
+
 long kvm_arch_vm_ioctl(struct file *filp,
 		       unsigned int ioctl, unsigned long arg)
 {
@@ -2488,6 +2560,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		}
 		break;
 	}
+	case KVM_S390_MEM_OP: {
+		struct kvm_s390_mem_op mem_op;
+
+		if (copy_from_user(&mem_op, argp, sizeof(mem_op)) == 0)
+			r = kvm_s390_vm_mem_op(kvm, &mem_op);
+		else
+			r = -EFAULT;
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}