CVE-2025-40102

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

KVM: arm64: Prevent access to vCPU events before init

Another day, another syzkaller bug. KVM erroneously allows userspace to

pend vCPU events for a vCPU that hasn't been initialized yet, leading to

KVM interpreting a bunch of uninitialized garbage for routing /

injecting the exception.

In one case the injection code and the hyp disagree on whether the vCPU

has a 32bit EL1 and put the vCPU into an illegal mode for AArch64,

tripping the BUG() in exception_target_el() during the next injection:

kernel BUG at arch/arm64/kvm/inject_fault.c:40!

Internal error: Oops - BUG: 00000000f2000800 [#1] SMP

CPU: 3 UID: 0 PID: 318 Comm: repro Not tainted 6.17.0-rc4-00104-g10fd0285305d #6 PREEMPT

Hardware name: linux,dummy-virt (DT)

pstate: 21402009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)

pc : exception_target_el+0x88/0x8c

lr : pend_serror_exception+0x18/0x13c

sp : ffff800082f03a10

x29: ffff800082f03a10 x28: ffff0000cb132280 x27: 0000000000000000

x26: 0000000000000000 x25: ffff0000c2a99c20 x24: 0000000000000000

x23: 0000000000008000 x22: 0000000000000002 x21: 0000000000000004

x20: 0000000000008000 x19: ffff0000c2a99c20 x18: 0000000000000000

x17: 0000000000000000 x16: 0000000000000000 x15: 00000000200000c0

x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000

x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000

x8 : ffff800082f03af8 x7 : 0000000000000000 x6 : 0000000000000000

x5 : ffff800080f621f0 x4 : 0000000000000000 x3 : 0000000000000000

x2 : 000000000040009b x1 : 0000000000000003 x0 : ffff0000c2a99c20

Call trace:

exception_target_el+0x88/0x8c (P)

kvm_inject_serror_esr+0x40/0x3b4

__kvm_arm_vcpu_set_events+0xf0/0x100

kvm_arch_vcpu_ioctl+0x180/0x9d4

kvm_vcpu_ioctl+0x60c/0x9f4

__arm64_sys_ioctl+0xac/0x104

invoke_syscall+0x48/0x110

el0_svc_common.constprop.0+0x40/0xe0

do_el0_svc+0x1c/0x28

el0_svc+0x34/0xf0

el0t_64_sync_handler+0xa0/0xe4

el0t_64_sync+0x198/0x19c

Code: f946bc01 b4fffe61 9101e020 17fffff2 (d4210000)

Reject the ioctls outright as no sane VMM would call these before

KVM_ARM_VCPU_INIT anyway. Even if it did the exception would've been

thrown away by the eventual reset of the vCPU's state.