netdev - Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog load/unload

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Date:   Wed, 19 Sep 2018 17:59:33 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>
CC:     "David S . Miller" <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog
 load/unload

On 9/19/18 4:44 PM, Song Liu wrote:
>
>
>> On Sep 19, 2018, at 3:39 PM, Alexei Starovoitov <ast@...nel.org> wrote:
>>
>> use perf_event_mmap_bpf_prog() helper to notify user space
>> about JITed bpf programs.
>> Use RECORD_MMAP perf event to tell user space where JITed bpf program was loaded.
>> Use empty program name as unload indication.
>>
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>> ---
>> kernel/bpf/core.c | 22 ++++++++++++++++++++--
>> 1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 3f5bf1af0826..ddf11fdafd36 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -384,7 +384,7 @@ bpf_get_prog_addr_region(const struct bpf_prog *prog,
>> 	*symbol_end   = addr + hdr->pages * PAGE_SIZE;
>> }
>>
>> -static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
>> +static char *bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
>> {
>> 	const char *end = sym + KSYM_NAME_LEN;
>>
>> @@ -402,9 +402,10 @@ static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
>> 	sym += snprintf(sym, KSYM_NAME_LEN, "bpf_prog_");
>> 	sym  = bin2hex(sym, prog->tag, sizeof(prog->tag));
>> 	if (prog->aux->name[0])
>> -		snprintf(sym, (size_t)(end - sym), "_%s", prog->aux->name);
>> +		sym += snprintf(sym, (size_t)(end - sym), "_%s", prog->aux->name);
>> 	else
>> 		*sym = 0;
>> +	return sym;
>> }
>>
>> static __always_inline unsigned long
>> @@ -480,23 +481,40 @@ static bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp)
>>
>> void bpf_prog_kallsyms_add(struct bpf_prog *fp)
>> {
>> +	unsigned long symbol_start, symbol_end;
>> +	char buf[KSYM_NAME_LEN], *sym;
>> +
>> 	if (!bpf_prog_kallsyms_candidate(fp) ||
>> 	    !capable(CAP_SYS_ADMIN))
>> 		return;
>>
>> +	bpf_get_prog_addr_region(fp, &symbol_start, &symbol_end);
>> +	sym = bpf_get_prog_name(fp, buf);
>> +	sym++; /* sym - buf is the length of the name including trailing 0 */
>> +	while (!IS_ALIGNED(sym - buf, sizeof(u64)))
>> +		*sym++ = 0;
>
> nit: This logic feels a little weird to me. How about we wrap the extra logic
> in a separate function:
>
> size_t bpf_get_prog_name_u64_aligned(const struct bpf_prog fp, char *buf)

probably bpf_get_prog_name_u64_padded() ?
would be cleaner indeed.

Will send v2 once Peter and Arnaldo provide their feedback.

Thanks for reviewing!