[PATCH v6 39/44] KVM: VMX: Bug the VM if either MSR auto-load list is full

Sean Christopherson
2025-12-06T00:18:46Z

WARN and bug the VM if either MSR auto-load list is full when adding an
MSR to the lists, as the set of MSRs that KVM loads via the lists is
finite and entirely KVM controlled, i.e. overflowing the lists shouldn't
be possible in a fully released version of KVM. Terminate the VM as the
core KVM infrastructure has no insight as to _why_ an MSR is being added
to the list, and failure to load an MSR on VM-Enter and/or VM-Exit could
be fatal to the host. E.g. running the host with a guest-controlled PEBS
MSR could generate unexpected writes to the DS buffer and crash the host.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 38491962b2c1..2c50ebf4ff1b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1098,6 +1098,7 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
{
int i, j = 0;
struct msr_autoload *m = &vmx->msr_autoload;
+ struct kvm *kvm = vmx->vcpu.kvm;

switch (msr) {
case MSR_EFER:
@@ -1134,12 +1135,10 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
i = vmx_find_loadstore_msr_slot(&m->guest, msr);
j = vmx_find_loadstore_msr_slot(&m->host, msr);

- if ((i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS) ||
- (j < 0 && m->host.nr == MAX_NR_LOADSTORE_MSRS)) {
- printk_once(KERN_WARNING "Not enough msr switch entries. "
- "Can't add msr %x\n", msr);
+ if (KVM_BUG_ON(i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm) ||
+ KVM_BUG_ON(j < 0 && m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
return;
- }
+
if (i < 0) {
i = m->guest.nr++;
vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);
--
2.52.0.223.gf5cc29aaa4-goog