linux-kernel - [PATCH] s390/kvm: Reject memory region operations for ucontrol VMs

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Date: Mon, 24 Jun 2024 11:59:02 +0200
From: Christoph Schlameuss <schlameuss@...ux.ibm.com>
To: linux-s390@...r.kernel.org
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org
Subject: [PATCH] s390/kvm: Reject memory region operations for ucontrol VMs

This change rejects the KVM_SET_USER_MEMORY_REGION and
KVM_SET_USER_MEMORY_REGION2 ioctls when called on a ucontrol VM.
This is neccessary since ucontrol VMs have kvm->arch.gmap set to 0 and
would thus result in a null pointer dereference further in.
Memory management needs to be performed in userspace and using the
ioctls KVM_S390_UCAS_MAP and KVM_S390_UCAS_UNMAP.

Also improve s390 specific documentation for KVM_SET_USER_MEMORY_REGION
and KVM_SET_USER_MEMORY_REGION2.

Signed-off-by: Christoph Schlameuss <schlameuss@...ux.ibm.com>
---
 Documentation/virt/kvm/api.rst | 12 ++++++++++++
 arch/s390/kvm/kvm-s390.c       |  3 +++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index a71d91978d9e..eec8df1dde06 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1403,6 +1403,12 @@ Instead, an abort (data abort if the cause of the page-table update
 was a load or a store, instruction abort if it was an instruction
 fetch) is injected in the guest.
 
+S390:
+^^^^^
+
+Returns -EINVAL if the VM has the KVM_VM_S390_UCONTROL flag set.
+Returns -EINVAL if called on a protected VM.
+
 4.36 KVM_SET_TSS_ADDR
 ---------------------
 
@@ -6273,6 +6279,12 @@ state.  At VM creation time, all memory is shared, i.e. the PRIVATE attribute
 is '0' for all gfns.  Userspace can control whether memory is shared/private by
 toggling KVM_MEMORY_ATTRIBUTE_PRIVATE via KVM_SET_MEMORY_ATTRIBUTES as needed.
 
+S390:
+^^^^^
+
+Returns -EINVAL if the VM has the KVM_VM_S390_UCONTROL flag set.
+Returns -EINVAL if called on a protected VM.
+
 4.141 KVM_SET_MEMORY_ATTRIBUTES
 -------------------------------
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 82e9631cd9ef..854d0d1410be 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5748,6 +5748,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 {
 	gpa_t size;
 
+	if (kvm_is_ucontrol(kvm))
+		return -EINVAL;
+
 	/* When we are protected, we should not change the memory slots */
 	if (kvm_s390_pv_get_handle(kvm))
 		return -EINVAL;

base-commit: f2661062f16b2de5d7b6a5c42a9a5c96326b8454
-- 
2.45.2