Re: [PATCH bpf-next 4/5] selftests/bpf: add a selftest with __user tag

[Yonghong Song <yhs@fb.com>]

On 12/19/21 5:51 PM, Alexei Starovoitov wrote:
> On Thu, Dec 09, 2021 at 09:35:59AM -0800, Yonghong Song wrote:
>> Added a selftest with two __user usages: a __user pointer-type argument
>> and a __user pointer-type struct member. In both cases,
>> directly accessing the user memory will result verification failure.
> ...
>> diff --git a/tools/testing/selftests/bpf/progs/btf_type_tag_user.c b/tools/testing/selftests/bpf/progs/btf_type_tag_user.c
>> new file mode 100644
>> index 000000000000..e149854f42dd
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/btf_type_tag_user.c
>> @@ -0,0 +1,29 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2021 Facebook */
>> +#include "vmlinux.h"
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +struct bpf_testmod_btf_type_tag_1 {
>> +	int a;
>> +};
>> +
>> +struct bpf_testmod_btf_type_tag_2 {
>> +	struct bpf_testmod_btf_type_tag_1 *p;
>> +};
>> +
>> +int g;
>> +
>> +SEC("fentry/bpf_testmod_test_btf_type_tag_user_1")
>> +int BPF_PROG(test_user1, struct bpf_testmod_btf_type_tag_1 *arg)
>> +{
>> +	g = arg->a;
>> +	return 0;
>> +}
>> +
>> +SEC("fentry/bpf_testmod_test_btf_type_tag_user_2")
>> +int BPF_PROG(test_user2, struct bpf_testmod_btf_type_tag_2 *arg)
>> +{
>> +	g = arg->p->a;
>> +	return 0;
>> +}
> 
> This is a targeted synthetic test. Great, but can you add one
> that probes real kernel function like:
> getsockname(int fd, struct sockaddr __user *usockaddr
> or
> getpeername(int fd, struct sockaddr __user *usockaddr > and the bpf prog tries to deref usockaddr ?

Ack. Will do.