[PATCH 3.16 252/306] KVM: x86: fix missed SRCU usage in kvm_lapic_set_vapic_addr

Ben Hutchings
2017-02-15T23:11:45Z

From: Paolo Bonzini <pbonzini@redhat.com>

commit 7301d6abaea926d685832f7e1f0c37dd206b01f4 upstream.

Reported by syzkaller:

[ INFO: suspicious RCU usage. ]
4.9.0-rc4+ #47 Not tainted
-------------------------------
./include/linux/kvm_host.h:536 suspicious rcu_dereference_check() usage!

stack backtrace:
CPU: 1 PID: 6679 Comm: syz-executor Not tainted 4.9.0-rc4+ #47
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
ffff880039e2f6d0 ffffffff81c2e46b ffff88003e3a5b40 0000000000000000
0000000000000001 ffffffff83215600 ffff880039e2f700 ffffffff81334ea9
ffffc9000730b000 0000000000000004 ffff88003c4f8420 ffff88003d3f8000
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff81c2e46b>] dump_stack+0xb3/0x118 lib/dump_stack.c:51
[<ffffffff81334ea9>] lockdep_rcu_suspicious+0x139/0x180 kernel/locking/lockdep.c:4445
[< inline >] __kvm_memslots include/linux/kvm_host.h:534
[< inline >] kvm_memslots include/linux/kvm_host.h:541
[<ffffffff8105d6ae>] kvm_gfn_to_hva_cache_init+0xa1e/0xce0 virt/kvm/kvm_main.c:1941
[<ffffffff8112685d>] kvm_lapic_set_vapic_addr+0xed/0x140 arch/x86/kvm/lapic.c:2217

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: fda4e2e85589191b123d31cdc21fd33ee70f50fd
Cc: Andrew Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/x86/kvm/x86.c | 3 +++
1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3305,6 +3305,7 @@ long kvm_arch_vcpu_ioctl(struct file *fi
};
case KVM_SET_VAPIC_ADDR: {
struct kvm_vapic_addr va;
+ int idx;

r = -EINVAL;
if (!irqchip_in_kernel(vcpu->kvm))
@@ -3312,7 +3313,9 @@ long kvm_arch_vcpu_ioctl(struct file *fi
r = -EFAULT;
if (copy_from_user(&va, argp, sizeof va))
goto out;
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
r = kvm_lapic_set_vapic_addr(vcpu, va.vapic_addr);
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
break;
}
case KVM_X86_SETUP_MCE: {