Re: [PATCH v8 bpf-next 4/9] bpf: use prog->jited_len in bpf_prog_ksym_set_addr()

Song Liu
2022-02-04T18:05:51Z

> On Feb 3, 2022, at 11:41 PM, Song Liu <song@kernel.org> wrote:
>
> On Mon, Jan 31, 2022 at 10:31 PM Song Liu <song@kernel.org> wrote:
>>
>> Using prog->jited_len is simpler and more accurate than current
>> estimation (header + header->size).
>>
>> Signed-off-by: Song Liu <song@kernel.org>
>
> Hmm... CI [1] reports error on test_progs 159/tailcalls, and bisect points to
> this one. However, I couldn't figure out why this breaks tail call.
> round_up(PAGE_SIZE) does fix it though. But that won't be accurate, right?
>
> Any suggestions on what could be the reason for these failures?
>
> Thanks,
> Song
>
> [1] https://github.com/kernel-patches/bpf/runs/5060194776?check_suite_focus=true

I guess this is the missing piece:

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1ae41d0cf96c..bbef86cb4e72 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13067,6 +13067,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)

prog->jited = 1;
prog->bpf_func = func[0]->bpf_func;
+ prog->jited_len = func[0]->jited_len;
prog->aux->func = func;
prog->aux->func_cnt = env->subprog_cnt;
bpf_prog_jit_attempt_done(prog);

Will send v9 with this.

>
>> ---
>> kernel/bpf/core.c | 5 +----
>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 14199228a6f0..e3fe53df0a71 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -537,13 +537,10 @@ long bpf_jit_limit_max __read_mostly;
>> static void
>> bpf_prog_ksym_set_addr(struct bpf_prog *prog)
>> {
>> - const struct bpf_binary_header *hdr = bpf_jit_binary_hdr(prog);
>> - unsigned long addr = (unsigned long)hdr;
>> -
>> WARN_ON_ONCE(!bpf_prog_ebpf_jited(prog));
>>
>> prog->aux->ksym.start = (unsigned long) prog->bpf_func;
>> - prog->aux->ksym.end = addr + hdr->size;
>> + prog->aux->ksym.end = prog->aux->ksym.start + prog->jited_len;
>> }
>>
>> static void
>> --
>> 2.30.2
>>