linux-kernel - [PATCH v2] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu

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Date:   Fri,  8 Jul 2022 14:51:47 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()

'vector' and 'trig_mode' fields of 'struct kvm_lapic_irq' are left
uninitialized in kvm_pv_kick_cpu_op(). While these fields are normally
not needed for APIC_DM_REMRD, they're still referenced by
__apic_accept_irq() for trace_kvm_apic_accept_irq(). Fully initialize
the structure to avoid consuming random stack memory.

Fixes: a183b638b61c ("KVM: x86: make apic_accept_irq tracepoint more generic")
Reported-by: syzbot+d6caa905917d353f0d07@...kaller.appspotmail.com
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
- Changes since v1:
  Only set fields which matter for APIC_DM_REMRD and defer
  initialization of the rest to the compiler [Sean].
---
 arch/x86/kvm/x86.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 567d13405445..6364da034462 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9340,15 +9340,17 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
  */
 static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
 {
-	struct kvm_lapic_irq lapic_irq;
-
-	lapic_irq.shorthand = APIC_DEST_NOSHORT;
-	lapic_irq.dest_mode = APIC_DEST_PHYSICAL;
-	lapic_irq.level = 0;
-	lapic_irq.dest_id = apicid;
-	lapic_irq.msi_redir_hint = false;
+	/*
+	 * All other fields are unused for APIC_DM_REMRD, but may be consumed by
+	 * common code, e.g. for tracing. Defer initialization to the compiler.
+	 */
+	struct kvm_lapic_irq lapic_irq = {
+		.delivery_mode = APIC_DM_REMRD,
+		.dest_mode = APIC_DEST_PHYSICAL,
+		.shorthand = APIC_DEST_NOSHORT,
+		.dest_id = apicid,
+	};
 
-	lapic_irq.delivery_mode = APIC_DM_REMRD;
 	kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
 }
 
-- 
2.35.3