selftests/bpf: Add test for BPF_NEG alu on CONST_PTR_TO_MAP

Add a test case for BPF_NEG operation on CONST_PTR_TO_MAP. Tests if
BPF_NEG operation on map_ptr is rejected in unprivileged mode and is a
scalar value and do not trigger Oops in privileged mode.

Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
Signed-off-by: Brahmajit Das <listout@listout.xyz>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251001191739.2323644-3-listout@listout.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: mannkafai

tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c

@@ -146,6 +146,24 @@ l0_%=:	exit;						\
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("map_ptr illegal alu op, map_ptr = -map_ptr")
+__failure __msg("R0 invalid mem access 'scalar'")
+__failure_unpriv __msg_unpriv("R0 pointer arithmetic prohibited")
+__flag(BPF_F_ANY_ALIGNMENT)
+__naked void map_ptr_illegal_alu_op(void)
+{
+	asm volatile ("					\
+	r0 = %[map_hash_48b] ll;			\
+	r0 = -r0;					\
+	r1 = 22;					\
+	*(u64*)(r0 + 0) = r1;				\
+	exit;						\
+"	:
+	: __imm_addr(map_hash_48b)
+	: __clobber_all);
+}
+
 SEC("flow_dissector")
 __description("flow_keys illegal alu op with variable offset")
 __failure __msg("R7 pointer arithmetic on flow_keys prohibited")