[PATCH -next 1/2] bpf: Unify data extension operation of jited_ksyms and jited_linfo
Pu Lehui
pulehui at huawei.com
Fri May 6 17:48:23 PDT 2022
On 2022/5/7 5:01, Andrii Nakryiko wrote:
> On Thu, Apr 28, 2022 at 2:47 AM Pu Lehui <pulehui at huawei.com> wrote:
>>
>> Hi Andrii,
>>
>> On 2022/4/28 6:33, Andrii Nakryiko wrote:
>>> On Tue, Apr 26, 2022 at 6:40 AM Pu Lehui <pulehui at huawei.com> wrote:
>>>>
>>>> We found that 32-bit environment can not print bpf line info due
>>>> to data inconsistency between jited_ksyms[0] and jited_linfo[0].
>>>>
>>>> For example:
>>>> jited_kyms[0] = 0xb800067c, jited_linfo[0] = 0xffffffffb800067c
>>>>
>>>> We know that both of them store bpf func address, but due to the
>>>> different data extension operations when extended to u64, they may
>>>> not be the same. We need to unify the data extension operations of
>>>> them.
>>>>
>>>> Signed-off-by: Pu Lehui <pulehui at huawei.com>
>>>> ---
>>>> kernel/bpf/syscall.c | 5 ++++-
>>>> tools/lib/bpf/bpf_prog_linfo.c | 8 ++++----
>>>> tools/testing/selftests/bpf/prog_tests/btf.c | 18 +++++++++---------
>>>
>>> please split kernel changes, libbpf changes, and selftests/bpf changes
>>> into separate patches
>> Thanks for your review. Alright, I will split it next time.
>>
>>>
>>>> 3 files changed, 17 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>>>> index e9621cfa09f2..4c417c806d92 100644
>>>> --- a/kernel/bpf/syscall.c
>>>> +++ b/kernel/bpf/syscall.c
>>>> @@ -3868,13 +3868,16 @@ static int bpf_prog_get_info_by_fd(struct file *file,
>>>> info.nr_jited_line_info = 0;
>>>> if (info.nr_jited_line_info && ulen) {
>>>> if (bpf_dump_raw_ok(file->f_cred)) {
>>>> + unsigned long jited_linfo_addr;
>>>> __u64 __user *user_linfo;
>>>> u32 i;
>>>>
>>>> user_linfo = u64_to_user_ptr(info.jited_line_info);
>>>> ulen = min_t(u32, info.nr_jited_line_info, ulen);
>>>> for (i = 0; i < ulen; i++) {
>>>> - if (put_user((__u64)(long)prog->aux->jited_linfo[i],
>>>> + jited_linfo_addr = (unsigned long)
>>>> + prog->aux->jited_linfo[i];
>>>> + if (put_user((__u64) jited_linfo_addr,
>>>> &user_linfo[i]))
>>>> return -EFAULT;
>>>> }
>> Please let me to explain more detail, sorry if I'm wordy.
>> The main reason that 32-bit env does not print bpf line info is here:
>>
>> kernel/bpf/syscall.c:
>> bpf_prog_get_info_by_fd {
>> ...
>> user_ksyms = u64_to_user_ptr(info.jited_ksyms);
>> ksym_addr = (unsigned long)prog->aux->func[i]->bpf_func;
>> if (put_user((u64) ksym_addr, &user_ksyms[i]))
>> ...
>>
>> user_linfo = u64_to_user_ptr(info.jited_line_info);
>> if (put_user((__u64)(long)prog->aux->jited_linfo[i],
>> &user_linfo[i]))
>> ...
>> }
>>
>> In 32-bit env, ksym_addr and prog->aux->jited_linfo[0] both store the
>> 32-bit address of bpf_func, but the first one is zero-extension to u64,
>> while the other is sign-extension to u64.
>> For example:
>> prog->aux->func[0]->bpf_func = 0xb800067c
>> user_ksyms[0] = 0xb800067c, user_linfo[0] = 0xffffffffb800067c
>>
>> Both zero-extension and sign-extension are fine, but if operating
>> directly between them without casting in 32-bit env, there will have
>> some potential problems. Such as:
>>
>> tools/lib/bpf/bpf_prog_linfo.c:
>> dissect_jited_func {
>> ...
>> if (ksym_func[0] != *jited_linfo) //always missmatch in 32 env
>> goto errout;
>> ...
>> if (ksym_func[f] == *jited_linfo) {
>> ...
>> last_jited_linfo = *jited_linfo;
>> if (last_jited_linfo - ksym_func[f - 1] + 1 >
>> ksym_len[f - 1])
>> ...
>> }
>>
>> We could cast them to 32-bit data type, but I think unify data extension
>> operation will be better.
>>
>>>> diff --git a/tools/lib/bpf/bpf_prog_linfo.c b/tools/lib/bpf/bpf_prog_linfo.c
>>>> index 5c503096ef43..5cf41a563ef5 100644
>>>> --- a/tools/lib/bpf/bpf_prog_linfo.c
>>>> +++ b/tools/lib/bpf/bpf_prog_linfo.c
>>>> @@ -127,7 +127,7 @@ struct bpf_prog_linfo *bpf_prog_linfo__new(const struct bpf_prog_info *info)
>>>> prog_linfo->raw_linfo = malloc(data_sz);
>>>> if (!prog_linfo->raw_linfo)
>>>> goto err_free;
>>>> - memcpy(prog_linfo->raw_linfo, (void *)(long)info->line_info, data_sz);
>>>> + memcpy(prog_linfo->raw_linfo, (void *)(unsigned long)info->line_info, data_sz);
>>>>
>>>> nr_jited_func = info->nr_jited_ksyms;
>>>> if (!nr_jited_func ||
>>>> @@ -148,7 +148,7 @@ struct bpf_prog_linfo *bpf_prog_linfo__new(const struct bpf_prog_info *info)
>>>> if (!prog_linfo->raw_jited_linfo)
>>>> goto err_free;
>>>> memcpy(prog_linfo->raw_jited_linfo,
>>>> - (void *)(long)info->jited_line_info, data_sz);
>>>> + (void *)(unsigned long)info->jited_line_info, data_sz);
>>>>
>>>> /* Number of jited_line_info per jited func */
>>>> prog_linfo->nr_jited_linfo_per_func = malloc(nr_jited_func *
>>>> @@ -166,8 +166,8 @@ struct bpf_prog_linfo *bpf_prog_linfo__new(const struct bpf_prog_info *info)
>>>> goto err_free;
>>>>
>>>> if (dissect_jited_func(prog_linfo,
>>>> - (__u64 *)(long)info->jited_ksyms,
>>>> - (__u32 *)(long)info->jited_func_lens))
>>>> + (__u64 *)(unsigned long)info->jited_ksyms,
>>>> + (__u32 *)(unsigned long)info->jited_func_lens))
>>>
>>> so I'm trying to understand how this is changing anything for 32-bit
>>> architecture and I must be missing something, sorry if I'm being
>>> dense. The example you used below
>>>
>>> jited_kyms[0] = 0xb800067c, jited_linfo[0] = 0xffffffffb800067c
>>>
>>> Wouldn't (unsigned long)0xffffffffb800067c == (long)0xffffffffb800067c
>>> == 0xb800067c ?
>> If I understand correctly, info->jited_ksyms or info->jited_func_lens is
>> just a u64 address that point to the corresponding space. The bpf_func
>> address is stored in the item of info->jited_ksyms but not
>> info->jited_ksyms.
>>
>> And here, I may have misled you. Both (__u64 *)(long)info->jited_ksyms
>> and (__u64 *)(unsigned long)info->jited_ksyms are the same, I just want
>> to unify the style. I will remove them in v2.
>>
>> Please let me know if there is any problem with my understanding.
>>
>
> Thanks for explanation. I guess in my mind I was always sign extending
> 32-bit to 64-bit, but I think memory addresses are conceptually
> unsigned, so (unsigned long) casting makes more sense, and u64
> representation of 0xb800067c should be 0x00000000b800067c and not
> 0xffffffffb800067c. So your changes make sense, and I agree that
> libbpf-side changes for conceptual uniformity are also good.
>
Alright, I will pick them back in v3. Thanks.
>
>> Thanks,
>> Lehui
>>>
>>> isn't sizeof(long) == sizeof(void*) == 4?
>>>
>>> It would be nice if you could elaborate a bit more on what problems
>>> did you see in practice?
>>>
>>>> goto err_free;
>>>>
>>>> return prog_linfo;
>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
>>>> index 84aae639ddb5..d9ba1ec1d5b3 100644
>>>> --- a/tools/testing/selftests/bpf/prog_tests/btf.c
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/btf.c
>>>> @@ -6451,8 +6451,8 @@ static int test_get_linfo(const struct prog_info_raw_test *test,
>>>> info.nr_jited_line_info, jited_cnt,
>>>> info.line_info_rec_size, rec_size,
>>>> info.jited_line_info_rec_size, jited_rec_size,
>>>> - (void *)(long)info.line_info,
>>>> - (void *)(long)info.jited_line_info)) {
>>>> + (void *)(unsigned long)info.line_info,
>>>> + (void *)(unsigned long)info.jited_line_info)) {
>>>> err = -1;
>>>> goto done;
>>>> }
>>>> @@ -6500,8 +6500,8 @@ static int test_get_linfo(const struct prog_info_raw_test *test,
>>>> }
>>>>
>>>> if (CHECK(jited_linfo[0] != jited_ksyms[0],
>>>> - "jited_linfo[0]:%lx != jited_ksyms[0]:%lx",
>>>> - (long)(jited_linfo[0]), (long)(jited_ksyms[0]))) {
>>>> + "jited_linfo[0]:%llx != jited_ksyms[0]:%llx",
>>>> + jited_linfo[0], jited_ksyms[0])) {
>>>> err = -1;
>>>> goto done;
>>>> }
>>>> @@ -6519,16 +6519,16 @@ static int test_get_linfo(const struct prog_info_raw_test *test,
>>>> }
>>>>
>>>> if (CHECK(jited_linfo[i] <= jited_linfo[i - 1],
>>>> - "jited_linfo[%u]:%lx <= jited_linfo[%u]:%lx",
>>>> - i, (long)jited_linfo[i],
>>>> - i - 1, (long)(jited_linfo[i - 1]))) {
>>>> + "jited_linfo[%u]:%llx <= jited_linfo[%u]:%llx",
>>>> + i, jited_linfo[i],
>>>> + i - 1, (jited_linfo[i - 1]))) {
>>>> err = -1;
>>>> goto done;
>>>> }
>>>>
>>>> if (CHECK(jited_linfo[i] - cur_func_ksyms > cur_func_len,
>>>> - "jited_linfo[%u]:%lx - %lx > %u",
>>>> - i, (long)jited_linfo[i], (long)cur_func_ksyms,
>>>> + "jited_linfo[%u]:%llx - %llx > %u",
>>>> + i, jited_linfo[i], cur_func_ksyms,
>>>> cur_func_len)) {
>>>> err = -1;
>>>> goto done;
>>>> --
>>>> 2.25.1
>>>>
>>> .
>>>
> .
>
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