diff options
| author | Sean Christopherson <seanjc@google.com> | 2025-04-01 08:05:04 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2025-04-04 07:07:39 -0400 |
| commit | ef01cac401f18647d62720cf773d7bb0541827da (patch) | |
| tree | 84fe59c6e66c6a5d36777cc676aaefd89e01e14c /arch | |
| parent | 782f9feaa9517caf33186dcdd6b50a8f770ed29b (diff) | |
KVM: x86: Acquire SRCU in KVM_GET_MP_STATE to protect guest memory accesses
Acquire a lock on kvm->srcu when userspace is getting MP state to handle a
rather extreme edge case where "accepting" APIC events, i.e. processing
pending INIT or SIPI, can trigger accesses to guest memory. If the vCPU
is in L2 with INIT *and* a TRIPLE_FAULT request pending, then getting MP
state will trigger a nested VM-Exit by way of ->check_nested_events(), and
emuating the nested VM-Exit can access guest memory.
The splat was originally hit by syzkaller on a Google-internal kernel, and
reproduced on an upstream kernel by hacking the triple_fault_event_test
selftest to stuff a pending INIT, store an MSR on VM-Exit (to generate a
memory access on VMX), and do vcpu_mp_state_get() to trigger the scenario.
=============================
WARNING: suspicious RCU usage
6.14.0-rc3-b112d356288b-vmx/pi_lockdep_false_pos-lock #3 Not tainted
-----------------------------
include/linux/kvm_host.h:1058 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by triple_fault_ev/1256:
#0: ffff88810df5a330 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x8b/0x9a0 [kvm]
stack backtrace:
CPU: 11 UID: 1000 PID: 1256 Comm: triple_fault_ev Not tainted 6.14.0-rc3-b112d356288b-vmx #3
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
<TASK>
dump_stack_lvl+0x7f/0x90
lockdep_rcu_suspicious+0x144/0x190
kvm_vcpu_gfn_to_memslot+0x156/0x180 [kvm]
kvm_vcpu_read_guest+0x3e/0x90 [kvm]
read_and_check_msr_entry+0x2e/0x180 [kvm_intel]
__nested_vmx_vmexit+0x550/0xde0 [kvm_intel]
kvm_check_nested_events+0x1b/0x30 [kvm]
kvm_apic_accept_events+0x33/0x100 [kvm]
kvm_arch_vcpu_ioctl_get_mpstate+0x30/0x1d0 [kvm]
kvm_vcpu_ioctl+0x33e/0x9a0 [kvm]
__x64_sys_ioctl+0x8b/0xb0
do_syscall_64+0x6c/0x170
entry_SYSCALL_64_after_hwframe+0x4b/0x53
</TASK>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250401150504.829812-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c841817a914a..3712dde0bf9d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11786,6 +11786,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu, if (kvm_mpx_supported()) kvm_load_guest_fpu(vcpu); + kvm_vcpu_srcu_read_lock(vcpu); + r = kvm_apic_accept_events(vcpu); if (r < 0) goto out; @@ -11799,6 +11801,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu, mp_state->mp_state = vcpu->arch.mp_state; out: + kvm_vcpu_srcu_read_unlock(vcpu); + if (kvm_mpx_supported()) kvm_put_guest_fpu(vcpu); vcpu_put(vcpu); |