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| author |   Sean Christopherson <sean.j.christopherson@intel.com> | 2019-11-22 08:58:18 -0800 |
|---|---|---|
| committer |   Paolo Bonzini <pbonzini@redhat.com> | 2019-11-23 11:30:15 +0100 |
| commit | ad5996d9a0e8019c3ae5151e687939369acfe044 (patch) | |
| tree | 1dcfacc559d734d59e940804f1209dcaaa7c5efc | |
| parent | KVM: x86: Open code shared_msr_update() in its only caller (diff) | |
| download | linux-dev-ad5996d9a0e8019c3ae5151e687939369acfe044.tar.xz linux-dev-ad5996d9a0e8019c3ae5151e687939369acfe044.zip | |
KVM: x86: Grab KVM's srcu lock when setting nested state
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>
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f5db520f2ac3..3ed167e039e5 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4442,6 +4442,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp, case KVM_SET_NESTED_STATE: { 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) @@ -4465,7 +4466,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, && !(kvm_state.flags & KVM_STATE_NESTED_GUEST_MODE)) break; + 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); break; } case KVM_GET_SUPPORTED_HV_CPUID: { |