CVE-2022-48943

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: make apf token non-zero to fix bug

In current async pagefault logic, when a page is ready, KVM relies on

kvm_arch_can_dequeue_async_page_present() to determine whether to deliver

a READY event to the Guest. This function test token value of struct

kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a

READY event is finished by Guest. If value is zero meaning that a READY

event is done, so the KVM can deliver another.

But the kvm_arch_setup_async_pf() may produce a valid token with zero

value, which is confused with previous mention and may lead the loss of

this READY event.

This bug may cause task blocked forever in Guest:

INFO: task stress:7532 blocked for more than 1254 seconds.

Not tainted 5.10.0 #16

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:stress state:D stack: 0 pid: 7532 ppid: 1409

flags:0x00000080

Call Trace:

__schedule+0x1e7/0x650

schedule+0x46/0xb0

kvm_async_pf_task_wait_schedule+0xad/0xe0

? exit_to_user_mode_prepare+0x60/0x70

__kvm_handle_async_pf+0x4f/0xb0

? asm_exc_page_fault+0x8/0x30

exc_page_fault+0x6f/0x110

? asm_exc_page_fault+0x8/0x30

asm_exc_page_fault+0x1e/0x30

RIP: 0033:0x402d00

RSP: 002b:00007ffd31912500 EFLAGS: 00010206

RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0

RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0

RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086

R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000

R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000