From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Derek Yerger <derek@djy.llc>,
kernel@najdan.com, Thomas Lambertz <mail@thomaslambertz.de>,
Rik van Riel <riel@surriel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Borislav Petkov <bp@suse.de>, Dave Hansen <dave.hansen@intel.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH 3/4] KVM: x86: Revert "KVM: X86: Fix fpu state crash in kvm guest"
Date: Thu, 16 Jan 2020 22:26:27 -0800 [thread overview]
Message-ID: <20200117062628.6233-4-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20200117062628.6233-1-sean.j.christopherson@intel.com>
Reload the current thread's FPU state, which contains the guest's FPU
state, to the CPU registers if necessary during vcpu_enter_guest().
TIF_NEED_FPU_LOAD can be set any time control is transferred out of KVM,
e.g. if I/O is triggered during a KVM call to get_user_pages() or if a
softirq occurs while KVM is scheduled in.
Moving the handling of TIF_NEED_FPU_LOAD from vcpu_enter_guest() to
kvm_arch_vcpu_load(), effectively kvm_sched_in(), papered over a bug
where kvm_put_guest_fpu() failed to account for TIF_NEED_FPU_LOAD. The
easiest way to the kvm_put_guest_fpu() bug was to run with involuntary
preemption enable, thus handling TIF_NEED_FPU_LOAD during kvm_sched_in()
made the bug go away. But, removing the handling in vcpu_enter_guest()
exposed KVM to the rare case of a softirq triggering kernel_fpu_begin()
between vcpu_load() and vcpu_enter_guest().
Now that kvm_{load,put}_guest_fpu() correctly handle TIF_NEED_FPU_LOAD,
revert the commit to both restore the vcpu_enter_guest() behavior and
eliminate the superfluous switch_fpu_return() in kvm_arch_vcpu_load().
Note, leaving the handling in kvm_arch_vcpu_load() isn't wrong per se,
but it is unnecessary, and most critically, makes it extremely difficult
to find bugs such as the kvm_put_guest_fpu() issue due to shrinking the
window where a softirq can corrupt state.
A sample trace triggered by warning if TIF_NEED_FPU_LOAD is set while
vcpu state is loaded:
<IRQ>
gcmaes_crypt_by_sg.constprop.12+0x26e/0x660
? 0xffffffffc024547d
? __qdisc_run+0x83/0x510
? __dev_queue_xmit+0x45e/0x990
? ip_finish_output2+0x1a8/0x570
? fib4_rule_action+0x61/0x70
? fib4_rule_action+0x70/0x70
? fib_rules_lookup+0x13f/0x1c0
? helper_rfc4106_decrypt+0x82/0xa0
? crypto_aead_decrypt+0x40/0x70
? crypto_aead_decrypt+0x40/0x70
? crypto_aead_decrypt+0x40/0x70
? esp_output_tail+0x8f4/0xa5a [esp4]
? skb_ext_add+0xd3/0x170
? xfrm_input+0x7a6/0x12c0
? xfrm4_rcv_encap+0xae/0xd0
? xfrm4_transport_finish+0x200/0x200
? udp_queue_rcv_one_skb+0x1ba/0x460
? udp_unicast_rcv_skb.isra.63+0x72/0x90
? __udp4_lib_rcv+0x51b/0xb00
? ip_protocol_deliver_rcu+0xd2/0x1c0
? ip_local_deliver_finish+0x44/0x50
? ip_local_deliver+0xe0/0xf0
? ip_protocol_deliver_rcu+0x1c0/0x1c0
? ip_rcv+0xbc/0xd0
? ip_rcv_finish_core.isra.19+0x380/0x380
? __netif_receive_skb_one_core+0x7e/0x90
? netif_receive_skb_internal+0x3d/0xb0
? napi_gro_receive+0xed/0x150
? 0xffffffffc0243c77
? net_rx_action+0x149/0x3b0
? __do_softirq+0xe4/0x2f8
? handle_irq_event_percpu+0x6a/0x80
? irq_exit+0xe6/0xf0
? do_IRQ+0x7f/0xd0
? common_interrupt+0xf/0xf
</IRQ>
? irq_entries_start+0x20/0x660
? vmx_get_interrupt_shadow+0x2f0/0x710 [kvm_intel]
? kvm_set_msr_common+0xfc7/0x2380 [kvm]
? recalibrate_cpu_khz+0x10/0x10
? ktime_get+0x3a/0xa0
? kvm_arch_vcpu_ioctl_run+0x107/0x560 [kvm]
? kvm_init+0x6bf/0xd00 [kvm]
? __seccomp_filter+0x7a/0x680
? do_vfs_ioctl+0xa4/0x630
? security_file_ioctl+0x32/0x50
? ksys_ioctl+0x60/0x90
? __x64_sys_ioctl+0x16/0x20
? do_syscall_64+0x5f/0x1a0
? entry_SYSCALL_64_after_hwframe+0x44/0xa9
---[ end trace 9564a1ccad733a90 ]---
This reverts commit e751732486eb3f159089a64d1901992b1357e7cc.
Fixes: e751732486eb3 ("KVM: X86: Fix fpu state crash in kvm guest")
Reported-by: Derek Yerger <derek@djy.llc>
Reported-by: kernel@najdan.com
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Thomas Lambertz <mail@thomaslambertz.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/x86.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0c7211491f98..ac290b7cc4d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3458,10 +3458,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_x86_ops->vcpu_load(vcpu, cpu);
- fpregs_assert_state_consistent();
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
- switch_fpu_return();
-
/* Apply any externally detected TSC adjustments (due to suspend) */
if (unlikely(vcpu->arch.tsc_offset_adjustment)) {
adjust_tsc_offset_host(vcpu, vcpu->arch.tsc_offset_adjustment);
@@ -8198,8 +8194,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
trace_kvm_entry(vcpu->vcpu_id);
guest_enter_irqoff();
- /* The preempt notifier should have taken care of the FPU already. */
- WARN_ON_ONCE(test_thread_flag(TIF_NEED_FPU_LOAD));
+ fpregs_assert_state_consistent();
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ switch_fpu_return();
if (unlikely(vcpu->arch.switch_db_regs)) {
set_debugreg(0, 7);
--
2.24.1
next prev parent reply other threads:[~2020-01-17 6:26 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 6:26 [PATCH 0/4] KVM: x86: TIF_NEED_FPU_LOAD bug fixes Sean Christopherson
2020-01-17 6:26 ` [PATCH 1/4] KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu() Sean Christopherson
2020-01-17 18:31 ` Dave Hansen
2020-01-17 18:43 ` Sean Christopherson
2020-01-17 6:26 ` [PATCH 2/4] KVM: x86: Ensure guest's FPU state is loaded when accessing for emulation Sean Christopherson
2020-01-17 6:26 ` Sean Christopherson [this message]
2020-03-04 7:41 ` [PATCH 3/4] KVM: x86: Revert "KVM: X86: Fix fpu state crash in kvm guest" Liu, Jing2
2020-03-04 7:58 ` Paolo Bonzini
2020-01-17 6:26 ` [PATCH 4/4] KVM: x86: Remove unused ctxt param from emulator's FPU accessors Sean Christopherson
2020-03-04 7:38 ` [PATCH 0/4] KVM: x86: TIF_NEED_FPU_LOAD bug fixes Liu, Jing2
2020-03-04 15:24 ` Sean Christopherson
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