linux-kernel - [PATCH 14/14] KVM: arm64: Prevent late calls to __pkvm_create_private

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Message-Id: <20210719104735.3681732-15-qperret@google.com>
Date:   Mon, 19 Jul 2021 11:47:35 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        tabba@...gle.com, dbrazdil@...gle.com, kernel-team@...roid.com,
        Quentin Perret <qperret@...gle.com>
Subject: [PATCH 14/14] KVM: arm64: Prevent late calls to __pkvm_create_private_mapping()

__pkvm_create_private_mapping() allows the host kernel to create
arbitrary mappings the hypervisor's "private" range. However, this is
only needed early on, and there should be no good reason for the host
to need this past the point where the pkvm static is set. Make sure to
stub the hypercall past this point to ensure it can't be used by a
malicious host.

Signed-off-by: Quentin Perret <qperret@...gle.com>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index f05ecbd382d0..e1d12f8122a7 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -154,7 +154,10 @@ static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ct
 	DECLARE_REG(size_t, size, host_ctxt, 2);
 	DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 3);
 
-	cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, prot);
+	if (static_branch_unlikely(&kvm_protected_mode_initialized))
+		cpu_reg(host_ctxt, 1) = -EPERM;
+	else
+		cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, prot);
 }
 
 static void handle___pkvm_prot_finalize(struct kvm_cpu_context *host_ctxt)
-- 
2.32.0.402.g57bb445576-goog