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>
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;