From 218bf772bddd221489c38dde6ef8e917131161f6 Mon Sep 17 00:00:00 2001 From: Jim Mattson Date: Wed, 2 Jun 2021 13:52:24 -0700 Subject: [PATCH] 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: <20210602205224.3189316-1-jmattson@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 3 +++ 1 file changed, 3 insertions(+) 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; -- 2.11.0