bpf: add new negative selftests to cover missing check_func_arg_reg_off() and reg->type check

Add new negative selftests which are intended to cover the
out-of-bounds memory access that could be performed on a
CONST_PTR_TO_DYNPTR within functions taking a ARG_PTR_TO_DYNPTR |
MEM_RDONLY as an argument, and acceptance of invalid register types
i.e. PTR_TO_BTF_ID within functions taking a ARG_PTR_TO_DYNPTR |
MEM_RDONLY.

Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Link: https://lore.kernel.org/r/20240625062857.92760-2-mattbobrowski@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -1686,3 +1686,27 @@ int test_dynptr_skb_small_buff(struct __sk_buff *skb)
 
 	return !!data;
 }
+
+__noinline long global_call_bpf_dynptr(const struct bpf_dynptr *dynptr)
+{
+	long ret = 0;
+	/* Avoid leaving this global function empty to avoid having the compiler
+	 * optimize away the call to this global function.
+	 */
+	__sink(ret);
+	return ret;
+}
+
+SEC("?raw_tp")
+__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
+int test_dynptr_reg_type(void *ctx)
+{
+	struct task_struct *current = NULL;
+	/* R1 should be holding a PTR_TO_BTF_ID, so this shouldn't be a
+	 * reg->type that can be passed to a function accepting a
+	 * ARG_PTR_TO_DYNPTR | MEM_RDONLY. process_dynptr_func() should catch
+	 * this.
+	 */
+	global_call_bpf_dynptr((const struct bpf_dynptr *)current);
+	return 0;
+}

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

@@ -45,7 +45,7 @@ int BPF_PROG(not_valid_dynptr, int cmd, union bpf_attr *attr, unsigned int size)
 }
 
 SEC("?lsm.s/bpf")
-__failure __msg("arg#0 expected pointer to stack or dynptr_ptr")
+__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
 int BPF_PROG(not_ptr_to_stack, int cmd, union bpf_attr *attr, unsigned int size)
 {
 	unsigned long val = 0;

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

@@ -29,7 +29,7 @@ int kfunc_dynptr_nullable_test2(struct __sk_buff *skb)
 }
 
 SEC("tc")
-__failure __msg("expected pointer to stack or dynptr_ptr")
+__failure __msg("expected pointer to stack or const struct bpf_dynptr")
 int kfunc_dynptr_nullable_test3(struct __sk_buff *skb)
 {
 	struct bpf_dynptr data;

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

@@ -221,3 +221,25 @@ int user_ringbuf_callback_reinit_dynptr_ringbuf(void *ctx)
 	bpf_user_ringbuf_drain(&user_ringbuf, try_reinit_dynptr_ringbuf, NULL, 0);
 	return 0;
 }
+
+__noinline long global_call_bpf_dynptr_data(struct bpf_dynptr *dynptr)
+{
+	bpf_dynptr_data(dynptr, 0xA, 0xA);
+	return 0;
+}
+
+static long callback_adjust_bpf_dynptr_reg_off(struct bpf_dynptr *dynptr,
+					       void *ctx)
+{
+	global_call_bpf_dynptr_data(dynptr += 1024);
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("dereference of modified dynptr_ptr ptr R1 off=16384 disallowed")
+int user_ringbuf_callback_const_ptr_to_dynptr_reg_off(void *ctx)
+{
+	bpf_user_ringbuf_drain(&user_ringbuf,
+			       callback_adjust_bpf_dynptr_reg_off, NULL, 0);
+	return 0;
+}