diff options
authorSean Christopherson <sean.j.christopherson@intel.com>2019-11-22 08:58:18 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-12-13 08:52:46 +0100
commit5cbc7ff56097659c5e41e884cff34731ea03e23a (patch)
parent6a10f818a9adbe394eb36d223814e207e5121236 (diff)
KVM: x86: Grab KVM's srcu lock when setting nested state
commit ad5996d9a0e8019c3ae5151e687939369acfe044 upstream. Acquire kvm->srcu for the duration of ->set_nested_state() to fix a bug where nVMX derefences ->memslots without holding ->srcu or ->slots_lock. The other half of nested migration, ->get_nested_state(), does not need to acquire ->srcu as it is a purely a dump of internal KVM (and CPU) state to userspace. Detected as an RCU lockdep splat that is 100% reproducible by running KVM's state_test selftest with CONFIG_PROVE_LOCKING=y. Note that the failing function, kvm_is_visible_gfn(), is only checking the validity of a gfn, it's not actually accessing guest memory (which is more or less unsupported during vmx_set_nested_state() due to incorrect MMU state), i.e. vmx_set_nested_state() itself isn't fundamentally broken. In any case, setting nested state isn't a fast path so there's no reason to go out of our way to avoid taking ->srcu. ============================= WARNING: suspicious RCU usage 5.4.0-rc7+ #94 Not tainted ----------------------------- include/linux/kvm_host.h:626 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by evmcs_test/10939: #0: ffff88826ffcb800 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0x85/0x630 [kvm] stack backtrace: CPU: 1 PID: 10939 Comm: evmcs_test Not tainted 5.4.0-rc7+ #94 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack+0x68/0x9b kvm_is_visible_gfn+0x179/0x180 [kvm] mmu_check_root+0x11/0x30 [kvm] fast_cr3_switch+0x40/0x120 [kvm] kvm_mmu_new_cr3+0x34/0x60 [kvm] nested_vmx_load_cr3+0xbd/0x1f0 [kvm_intel] nested_vmx_enter_non_root_mode+0xab8/0x1d60 [kvm_intel] vmx_set_nested_state+0x256/0x340 [kvm_intel] kvm_arch_vcpu_ioctl+0x491/0x11a0 [kvm] kvm_vcpu_ioctl+0xde/0x630 [kvm] do_vfs_ioctl+0xa2/0x6c0 ksys_ioctl+0x66/0x70 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x54/0x200 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7f59a2b95f47 Fixes: 8fcc4b5923af5 ("kvm: nVMX: Introduce KVM_CAP_NESTED_STATE") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 68dd949bc0eb..353f63f3b262 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4117,6 +4117,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
struct kvm_nested_state __user *user_kvm_nested_state = argp;
struct kvm_nested_state kvm_state;
+ int idx;
r = -EINVAL;
if (!kvm_x86_ops->set_nested_state)
@@ -4138,7 +4139,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
if (kvm_state.flags == KVM_STATE_NESTED_RUN_PENDING)
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
r = kvm_x86_ops->set_nested_state(vcpu, user_kvm_nested_state, &kvm_state);
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);