LoongArch: BPF: Prevent out-of-bounds memory access

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

LoongArch: BPF: Prevent out-of-bounds memory access

The test_tag test triggers an unhandled page fault:

# ./test_tag
[ 130.640218] CPU 0 Unable to handle kernel paging request at virtual address ffff80001b898004, era == 9000000003137f7c, ra == 9000000003139e70
[ 130.640501] Oops[#3]:
[ 130.640553] CPU: 0 PID: 1326 Comm: test_tag Tainted: G D O 6.7.0-rc4-loong-devel-gb62ab1a397cf #47 61985c1d94084daa2432f771daa45b56b10d8d2a
[ 130.640764] Hardware name: QEMU QEMU Virtual Machine, BIOS unknown 2/2/2022
[ 130.640874] pc 9000000003137f7c ra 9000000003139e70 tp 9000000104cb4000 sp 9000000104cb7a40
[ 130.641001] a0 ffff80001b894000 a1 ffff80001b897ff8 a2 000000006ba210be a3 0000000000000000
[ 130.641128] a4 000000006ba210be a5 00000000000000f1 a6 00000000000000b3 a7 0000000000000000
[ 130.641256] t0 0000000000000000 t1 00000000000007f6 t2 0000000000000000 t3 9000000004091b70
[ 130.641387] t4 000000006ba210be t5 0000000000000004 t6 fffffffffffffff0 t7 90000000040913e0
[ 130.641512] t8 0000000000000005 u0 0000000000000dc0 s9 0000000000000009 s0 9000000104cb7ae0
[ 130.641641] s1 00000000000007f6 s2 0000000000000009 s3 0000000000000095 s4 0000000000000000
[ 130.641771] s5 ffff80001b894000 s6 ffff80001b897fb0 s7 9000000004090c50 s8 0000000000000000
[ 130.641900] ra: 9000000003139e70 build_body+0x1fcc/0x4988
[ 130.642007] ERA: 9000000003137f7c build_body+0xd8/0x4988
[ 130.642112] CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
[ 130.642261] PRMD: 00000004 (PPLV0 +PIE -PWE)
[ 130.642353] EUEN: 00000003 (+FPE +SXE -ASXE -BTE)
[ 130.642458] ECFG: 00071c1c (LIE=2-4,10-12 VS=7)
[ 130.642554] ESTAT: 00010000 [PIL] (IS= ECode=1 EsubCode=0)
[ 130.642658] BADV: ffff80001b898004
[ 130.642719] PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
[ 130.642815] Modules linked in: [last unloaded: bpf_testmod(O)]
[ 130.642924] Process test_tag (pid: 1326, threadinfo=00000000f7f4015f, task=000000006499f9fd)
[ 130.643062] Stack : 0000000000000000 9000000003380724 0000000000000000 0000000104cb7be8
[ 130.643213] 0000000000000000 25af8d9b6e600558 9000000106250ea0 9000000104cb7ae0
[ 130.643378] 0000000000000000 0000000000000000 9000000104cb7be8 90000000049f6000
[ 130.643538] 0000000000000090 9000000106250ea0 ffff80001b894000 ffff80001b894000
[ 130.643685] 00007ffffb917790 900000000313ca94 0000000000000000 0000000000000000
[ 130.643831] ffff80001b894000 0000000000000ff7 0000000000000000 9000000100468000
[ 130.643983] 0000000000000000 0000000000000000 0000000000000040 25af8d9b6e600558
[ 130.644131] 0000000000000bb7 ffff80001b894048 0000000000000000 0000000000000000
[ 130.644276] 9000000104cb7be8 90000000049f6000 0000000000000090 9000000104cb7bdc
[ 130.644423] ffff80001b894000 0000000000000000 00007ffffb917790 90000000032acfb0
[ 130.644572] ...
[ 130.644629] Call Trace:
[ 130.644641] [<9000000003137f7c>] build_body+0xd8/0x4988
[ 130.644785] [<900000000313ca94>] bpf_int_jit_compile+0x228/0x4ec
[ 130.644891] [<90000000032acfb0>] bpf_prog_select_runtime+0x158/0x1b0
[ 130.645003] [<90000000032b3504>] bpf_prog_load+0x760/0xb44
[ 130.645089] [<90000000032b6744>] __sys_bpf+0xbb8/0x2588
[ 130.645175] [<90000000032b8388>] sys_bpf+0x20/0x2c
[ 130.645259] [<9000000003f6ab38>] do_syscall+0x7c/0x94
[ 130.645369] [<9000000003121c5c>] handle_syscall+0xbc/0x158
[ 130.645507]
[ 130.645539] Code: 380839f6 380831f9 28412bae <24000ca6> 004081ad 0014cb50 004083e8 02bff34c 58008e91
[ 130.645729]
[ 130.646418] ---[ end trace 0000000000000000 ]---

On my machine, which has CONFIG_PAGE_SIZE_16KB=y, the test failed at
loading a BPF prog with 2039 instructions:

prog = (struct bpf_prog *)ffff80001b894000
insn = (struct bpf_insn *)(prog->insnsi)fff
---truncated---