path: root/arch/x86
diff options
authorJim Mattson <>2021-06-02 13:52:24 -0700
committerPaolo Bonzini <>2021-06-09 17:25:37 -0400
commit218bf772bddd221489c38dde6ef8e917131161f6 (patch)
treedd4cbdfa4caa3660908846cbc154b34514fe006b /arch/x86
parent4422829e8053068e0225e4d0ef42dc41ea7c9ef5 (diff)
kvm: LAPIC: Restore guard to prevent illegal APIC register access
Per the SDM, "any access that touches bytes 4 through 15 of an APIC register may cause undefined behavior and must not be executed." Worse, such an access in kvm_lapic_reg_read can result in a leak of kernel stack contents. Prior to commit 01402cf81051 ("kvm: LAPIC: write down valid APIC registers"), such an access was explicitly disallowed. Restore the guard that was removed in that commit. Fixes: 01402cf81051 ("kvm: LAPIC: write down valid APIC registers") Signed-off-by: Jim Mattson <> Reported-by: syzbot <> Message-Id: <> Signed-off-by: Paolo Bonzini <>
Diffstat (limited to 'arch/x86')
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 6d72d8f43310..17fa4ab1b834 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1410,6 +1410,9 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
if (!apic_x2apic_mode(apic))
valid_reg_mask |= APIC_REG_MASK(APIC_ARBPRI);
+ if (alignment + len > 4)
+ return 1;
if (offset > 0x3f0 || !(valid_reg_mask & APIC_REG_MASK(offset)))
return 1;