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linux/virt/kvm
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Breno Leitao 82bd728a06 KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 
commit 49f683b41f upstream.

Use {READ,WRITE}_ONCE() to access kvm->last_boosted_vcpu to ensure the
loads and stores are atomic.  In the extremely unlikely scenario the
compiler tears the stores, it's theoretically possible for KVM to attempt
to get a vCPU using an out-of-bounds index, e.g. if the write is split
into multiple 8-bit stores, and is paired with a 32-bit load on a VM with
257 vCPUs:

  CPU0                              CPU1
  last_boosted_vcpu = 0xff;

                                    (last_boosted_vcpu = 0x100)
                                    last_boosted_vcpu[15:8] = 0x01;
  i = (last_boosted_vcpu = 0x1ff)
                                    last_boosted_vcpu[7:0] = 0x00;

  vcpu = kvm->vcpu_array[0x1ff];

As detected by KCSAN:

  BUG: KCSAN: data-race in kvm_vcpu_on_spin [kvm] / kvm_vcpu_on_spin [kvm]

  write to 0xffffc90025a92344 of 4 bytes by task 4340 on cpu 16:
  kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112) kvm
  handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel
  vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?
		 arch/x86/kvm/vmx/vmx.c:6606) kvm_intel
  vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm
  kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm
  kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm
  __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)
  __x64_sys_ioctl (fs/ioctl.c:890)
  x64_sys_call (arch/x86/entry/syscall_64.c:33)
  do_syscall_64 (arch/x86/entry/common.c:?)
  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

  read to 0xffffc90025a92344 of 4 bytes by task 4342 on cpu 4:
  kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4069) kvm
  handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel
  vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?
			arch/x86/kvm/vmx/vmx.c:6606) kvm_intel
  vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm
  kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm
  kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm
  __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)
  __x64_sys_ioctl (fs/ioctl.c:890)
  x64_sys_call (arch/x86/entry/syscall_64.c:33)
  do_syscall_64 (arch/x86/entry/common.c:?)
  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

  value changed: 0x00000012 -> 0x00000000

Fixes: 217ece6129 ("KVM: use yield_to instead of sleep in kvm_vcpu_on_spin")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/20240510092353.2261824-1-leitao@debian.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2024-10-22 15:40:41 +02:00
..
async_pf.c KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-10 16:18:34 +02:00
async_pf.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 504 2019-06-19 17:09:56 +02:00
binary_stats.c KVM: stats: remove dead stores 2021-08-13 03:35:15 -04:00
coalesced_mmio.c KVM: Destroy target device if coalesced MMIO unregistration fails 2023-03-10 09:40:00 +01:00
coalesced_mmio.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dirty_ring.c KVM: Drop unused kvm_dirty_gfn_invalid() 2021-09-06 08:23:46 -04:00
eventfd.c KVM: eventfd: Fix false positive RCU usage warning 2022-02-16 12:56:16 +01:00
irqchip.c KVM/arm updates for 5.3 2019-07-11 15:14:16 +02:00
Kconfig kvm: add PM-notifier 2021-06-17 13:09:32 -04:00
kvm_main.c KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-10-22 15:40:41 +02:00
mmu_lock.h KVM: x86/mmu: Use an rwlock for the x86 MMU 2021-02-04 05:27:43 -05:00
vfio.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
vfio.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00