bpf: verifier: reject addr_space_cast insn without arena

The verifier allows using the addr_space_cast instruction in a program
that doesn't have an associated arena. This was caught in the form an
invalid memory access in do_misc_fixups() when while converting
addr_space_cast to a normal 32-bit mov, env->prog->aux->arena was
dereferenced to check for BPF_F_NO_USER_CONV flag.

Reject programs that include the addr_space_cast instruction but don't
have an associated arena.

root@rv-tester:~# ./reproducer
 Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000000000030
 Oops [#1]
 [<ffffffff8017eeaa>] do_misc_fixups+0x43c/0x1168
 [<ffffffff801936d6>] bpf_check+0xda8/0x22b6
 [<ffffffff80174b32>] bpf_prog_load+0x486/0x8dc
 [<ffffffff80176566>] __sys_bpf+0xbd8/0x214e
 [<ffffffff80177d14>] __riscv_sys_bpf+0x22/0x2a
 [<ffffffff80d2493a>] do_trap_ecall_u+0x102/0x17c
 [<ffffffff80d3048c>] ret_from_exception+0x0/0x64

Fixes: 6082b6c3 ("bpf: Recognize addr_space_cast instruction in the verifier.")
Reported-by: xingwei lee <xrivendell7@gmail.com>
Reported-by: yue sun <samsun1006219@gmail.com>
Closes: https://lore.kernel.org/bpf/CABOYnLz09O1+2gGVJuCxd_24a-7UueXzV-Ff+Fr+h5EKFDiYCQ@mail.gmail.com/Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Link: https://lore.kernel.org/r/20240322153518.11555-1-puranjay12@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -14022,6 +14022,10 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 					verbose(env, "addr_space_cast insn can only convert between address space 1 and 0\n");
 					return -EINVAL;
 				}
+				if (!env->prog->aux->arena) {
+					verbose(env, "addr_space_cast insn can only be used in a program that has an associated arena\n");
+					return -EINVAL;
+				}
 			} else {
 				if ((insn->off != 0 && insn->off != 8 && insn->off != 16 &&
 				     insn->off != 32) || insn->imm) {