[Devel] [PATCH RHEL7] KVM: LAPIC: Fix pv ipis use-before-initialization

[Valeriy Vdovin]

From: Wanpeng Li <kernellwp at gmail.com>

Reported by syzkaller:

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000014
 PGD 800000040410c067 P4D 800000040410c067 PUD 40410d067 PMD 0
 Oops: 0000 [#1] PREEMPT SMP PTI
 CPU: 3 PID: 2567 Comm: poc Tainted: G           OE     4.19.0-rc5 #16
 RIP: 0010:kvm_pv_send_ipi+0x94/0x350 [kvm]
 Call Trace:
  kvm_emulate_hypercall+0x3cc/0x700 [kvm]
  handle_vmcall+0xe/0x10 [kvm_intel]
  vmx_handle_exit+0xc1/0x11b0 [kvm_intel]
  vcpu_enter_guest+0x9fb/0x1910 [kvm]
  kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm]
  kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm]
  do_vfs_ioctl+0xa5/0x690
  ksys_ioctl+0x6d/0x80
  __x64_sys_ioctl+0x1a/0x20
  do_syscall_64+0x83/0x6e0
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The reason is that the apic map has not yet been initialized, the testcase
triggers pv_send_ipi interface by vmcall which results in kvm->arch.apic_map
is dereferenced. This patch fixes it by checking whether or not apic map is
NULL and bailing out immediately if that is the case.

Fixes: 4180bf1b65 (KVM: X86: Implement "send IPI" hypercall)
Reported-by: Wei Wu <ww9210 at gmail.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Krčmář <rkrcmar at redhat.com>
Cc: Wei Wu <ww9210 at gmail.com>
Signed-off-by: Wanpeng Li <wanpengli at tencent.com>
Cc: stable at vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>

(cherry-picked from commit 38ab012f109caf10f471db1adf284e620dd8d701)
https://jira.sw.ru/browse/PSBM-107931

Signed-off-by: Valeriy.Vdovin <valeriy.vdovin at virtuozzo.com>
---
 arch/x86/kvm/lapic.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 740be89..f433199 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -566,6 +566,11 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
 	rcu_read_lock();
 	map = rcu_dereference(kvm->arch.apic_map);
 
+	if (unlikely(!map)) {
+		count = -EOPNOTSUPP;
+		goto out;
+	}
+
 	if (min > map->max_apic_id)
 		goto out;
 	/* Bits above cluster_size are masked in the caller.  */
-- 
1.8.3.1