Messages in this thread Patch in this message | | | From | Pu Lehui <> | Subject | Re: [PATCH -next 1/2] bpf: Unify data extension operation of jited_ksyms and jited_linfo | Date | Thu, 28 Apr 2022 17:47:48 +0800 |
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Hi Andrii,
On 2022/4/28 6:33, Andrii Nakryiko wrote: > On Tue, Apr 26, 2022 at 6:40 AM Pu Lehui <pulehui@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@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, 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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