linux-kernel - [PATCH 3/3] KVM: x86: Explicitly zero kvm

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Date: Tue, 23 Apr 2024 09:53:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] KVM: x86: Explicitly zero kvm_caps during vendor module load

Zero out all of kvm_caps when loading a new vendor module to ensure that
KVM can't inadvertently rely on global initialization of a field, and add
a comment above the definition of kvm_caps to call out that all fields
needs to be explicitly computed during vendor module load.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44ce187bad89..8f3979d5fc80 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -92,6 +92,11 @@
 #define MAX_IO_MSRS 256
 #define KVM_MAX_MCE_BANKS 32
 
+/*
+ * Note, kvm_caps fields should *never* have default values, all fields must be
+ * recomputed from scratch during vendor module load, e.g. to account for a
+ * vendor module being reloaded with different module parameters.
+ */
 struct kvm_caps kvm_caps __read_mostly;
 EXPORT_SYMBOL_GPL(kvm_caps);
 
@@ -9755,6 +9760,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 		return -EIO;
 	}
 
+	memset(&kvm_caps, 0, sizeof(kvm_caps));
+
 	x86_emulator_cache = kvm_alloc_emulator_cache();
 	if (!x86_emulator_cache) {
 		pr_err("failed to allocate cache for x86 emulator\n");
-- 
2.44.0.769.g3c40516874-goog