LoongArch: KVM: Fix stack protector issue in send_ipi_data()

In the Linux kernel, the following vulnerability has been resolved: LoongArch: KVM: Fix stack protector issue in send_ipi_data() Function kvm_io_bus_read() is called in function send_ipi_data(), buffer size of parameter *val should be at least 8 bytes. Since some emulation functions like loongarch_ipi_readl() and kvm_eiointc_read() will write the buffer *val with 8 bytes signed extension regardless parameter len. Otherwise there will be buffer overflow issue when CONFIG_STACKPROTECTOR is enabled. The bug report is shown as follows: Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: send_ipi_data+0x194/0x1a0 [kvm] CPU: 11 UID: 107 PID: 2692 Comm: CPU 0/KVM Not tainted 6.17.0-rc1+ #102 PREEMPT(full) Stack : 9000000005901568 0000000000000000 9000000003af371c 900000013c68c000 900000013c68f850 900000013c68f858 0000000000000000 900000013c68f998 900000013c68f990 900000013c68f990 900000013c68f6c0 fffffffffffdb058 fffffffffffdb0e0 900000013c68f858 911e1d4d39cf0ec2 9000000105657a00 0000000000000001 fffffffffffffffe 0000000000000578 282049464555206e 6f73676e6f6f4c20 0000000000000001 00000000086b4000 0000000000000000 0000000000000000 0000000000000000 9000000005709968 90000000058f9000 900000013c68fa68 900000013c68fab4 90000000029279f0 900000010153f940 900000010001f360 0000000000000000 9000000003af3734 000000004390000c 00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d ... Call Trace: [<9000000003af3734>] show_stack+0x5c/0x180 [<9000000003aed168>] dump_stack_lvl+0x6c/0x9c [<9000000003ad0ab0>] vpanic+0x108/0x2c4 [<9000000003ad0ca8>] panic+0x3c/0x40 [<9000000004eb0a1c>] __stack_chk_fail+0x14/0x18 [<ffff8000023473f8>] send_ipi_data+0x190/0x1a0 [kvm] [<ffff8000023313e4>] __kvm_io_bus_write+0xa4/0xe8 [kvm] [<ffff80000233147c>] kvm_io_bus_write+0x54/0x90 [kvm] [<ffff80000233f9f8>] kvm_emu_iocsr+0x180/0x310 [kvm] [<ffff80000233fe08>] kvm_handle_gspr+0x280/0x478 [kvm] [<ffff8000023443e8>] kvm_handle_exit+0xc0/0x130 [kvm]