| Message ID | 20240723232055.3643811-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Acquire kvm->srcu when handling KVM_SET_VCPU_EVENTS | expand |
On Tue, 23 Jul 2024 16:20:55 -0700, Sean Christopherson wrote: > Grab kvm->srcu when processing KVM_SET_VCPU_EVENTS, as KVM will forcibly > leave nested VMX/SVM if SMM mode is being toggled, and leaving nested VMX > reads guest memory. > > Note, kvm_vcpu_ioctl_x86_set_vcpu_events() can also be called from KVM_RUN > via sync_regs(), which already holds SRCU. I.e. trying to precisely use > kvm_vcpu_srcu_read_lock() around the problematic SMM code would cause > problems. Acquiring SRCU isn't all that expensive, so for simplicity, > grab it unconditionally for KVM_SET_VCPU_EVENTS. > > [...] Applied to kvm-x86 fixes, thanks! [1/1] KVM: x86: Acquire kvm->srcu when handling KVM_SET_VCPU_EVENTS https://github.com/kvm-x86/linux/commit/4bcdd831d9d0 -- https://github.com/kvm-x86/linux/tree/next
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index af6c8cf6a37a..d3a4333807c6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6042,7 +6042,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, if (copy_from_user(&events, argp, sizeof(struct kvm_vcpu_events))) break; + kvm_vcpu_srcu_read_lock(vcpu); r = kvm_vcpu_ioctl_x86_set_vcpu_events(vcpu, &events); + kvm_vcpu_srcu_read_unlock(vcpu); break; } case KVM_GET_DEBUGREGS: {
Grab kvm->srcu when processing KVM_SET_VCPU_EVENTS, as KVM will forcibly leave nested VMX/SVM if SMM mode is being toggled, and leaving nested VMX reads guest memory. Note, kvm_vcpu_ioctl_x86_set_vcpu_events() can also be called from KVM_RUN via sync_regs(), which already holds SRCU. I.e. trying to precisely use kvm_vcpu_srcu_read_lock() around the problematic SMM code would cause problems. Acquiring SRCU isn't all that expensive, so for simplicity, grab it unconditionally for KVM_SET_VCPU_EVENTS. ============================= WARNING: suspicious RCU usage 6.10.0-rc7-332d2c1d713e-next-vm #552 Not tainted ----------------------------- include/linux/kvm_host.h:1027 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by repro/1071: #0: ffff88811e424430 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x7d/0x970 [kvm] stack backtrace: CPU: 15 PID: 1071 Comm: repro Not tainted 6.10.0-rc7-332d2c1d713e-next-vm #552 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+0x13f/0x1a0 kvm_vcpu_gfn_to_memslot+0x168/0x190 [kvm] kvm_vcpu_read_guest+0x3e/0x90 [kvm] nested_vmx_load_msr+0x6b/0x1d0 [kvm_intel] load_vmcs12_host_state+0x432/0xb40 [kvm_intel] vmx_leave_nested+0x30/0x40 [kvm_intel] kvm_vcpu_ioctl_x86_set_vcpu_events+0x15d/0x2b0 [kvm] kvm_arch_vcpu_ioctl+0x1107/0x1750 [kvm] ? mark_held_locks+0x49/0x70 ? kvm_vcpu_ioctl+0x7d/0x970 [kvm] ? kvm_vcpu_ioctl+0x497/0x970 [kvm] kvm_vcpu_ioctl+0x497/0x970 [kvm] ? lock_acquire+0xba/0x2d0 ? find_held_lock+0x2b/0x80 ? do_user_addr_fault+0x40c/0x6f0 ? lock_release+0xb7/0x270 __x64_sys_ioctl+0x82/0xb0 do_syscall_64+0x6c/0x170 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7ff11eb1b539 </TASK> Fixes: f7e570780efc ("KVM: x86: Forcibly leave nested virt when SMM state is toggled") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+) base-commit: 332d2c1d713e232e163386c35a3ba0c1b90df83f