linux-kernel - [RFC PATCH v4 08/39] KVM: arm64: Deny changes to locked memslots

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Date:   Wed, 25 Aug 2021 17:17:44 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        will@...nel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v4 08/39] KVM: arm64: Deny changes to locked memslots

Forbid userspace from making changes to a locked memslot. If userspace
wants to modify a locked memslot, then they will need to unlock it.

One special case is allowed: memslots locked for read, but not for write,
can have dirty page logging turned on.

Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
 arch/arm64/kvm/mmu.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 27b7befd4fa9..3ab8eba808ae 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1842,8 +1842,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 {
 	hva_t hva = mem->userspace_addr;
 	hva_t reg_end = hva + mem->memory_size;
+	struct kvm_memory_slot *old;
 	int ret = 0;
 
+	/*
+	 * Forbid all changes to locked memslots with the exception of turning
+	 * on dirty page logging for memslots locked only for reads.
+	 */
+	old = id_to_memslot(kvm_memslots(kvm), memslot->id);
+	if (old && memslot_is_locked(old)) {
+		if (change == KVM_MR_FLAGS_ONLY &&
+		    memslot_is_logging(memslot) &&
+		    !(old->arch.flags & KVM_MEMSLOT_LOCK_WRITE))
+			memcpy(&memslot->arch, &old->arch, sizeof(old->arch));
+		else
+			return -EBUSY;
+	}
+
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
 			change != KVM_MR_FLAGS_ONLY)
 		return 0;
-- 
2.33.0