From: Jim Mattson jmattson@google.com
[ Upstream commit 218bf772bddd221489c38dde6ef8e917131161f6 ]
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 jmattson@google.com Reported-by: syzbot syzkaller@googlegroups.com Message-Id: 20210602205224.3189316-1-jmattson@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 fa023f3feb25..43013ac0fd4d 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;