On 05/21/2018 09:42 PM, Sandipan Das wrote:
> On 05/18/2018 09:21 PM, Daniel Borkmann wrote:
>> On 05/18/2018 02:50 PM, Sandipan Das wrote:
>>> Currently, for multi-function programs, we cannot get the JITed
>>> instructions using the bpf system call's BPF_OBJ_GET_INFO_BY_FD
>>> command. Because of this, userspace tools such as bpftool fail
>>> to identify a multi-function program as being JITed or not.
>>>
>>> With the JIT enabled and the test program running, this can be
>>> verified as follows:
>>>
>>> # cat /proc/sys/net/core/bpf_jit_enable
>>> 1
>>>
>>> Before applying this patch:
>>>
>>> # bpftool prog list
>>> 1: kprobe name foo tag b811aab41a39ad3d gpl
>>> loaded_at 2018-05-16T11:43:38+0530 uid 0
>>> xlated 216B not jited memlock 65536B
>>> ...
>>>
>>> # bpftool prog dump jited id 1
>>> no instructions returned
>>>
>>> After applying this patch:
>>>
>>> # bpftool prog list
>>> 1: kprobe name foo tag b811aab41a39ad3d gpl
>>> loaded_at 2018-05-16T12:13:01+0530 uid 0
>>> xlated 216B jited 308B memlock 65536B
>>> ...
>>
>> That's really nice! One comment inline below:
>>
>>> # bpftool prog dump jited id 1
>>> 0: nop
>>> 4: nop
>>> 8: mflr r0
>>> c: std r0,16(r1)
>>> 10: stdu r1,-112(r1)
>>> 14: std r31,104(r1)
>>> 18: addi r31,r1,48
>>> 1c: li r3,10
>>> ...
>>>
>>> Signed-off-by: Sandipan Das <sandi...@linux.vnet.ibm.com>
>>> ---
>>> kernel/bpf/syscall.c | 38 ++++++++++++++++++++++++++++++++------
>>> 1 file changed, 32 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>>> index 54a72fafe57c..2430d159078c 100644
>>> --- a/kernel/bpf/syscall.c
>>> +++ b/kernel/bpf/syscall.c
>>> @@ -1896,7 +1896,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog
>>> *prog,
>>> struct bpf_prog_info info = {};
>>> u32 info_len = attr->info.info_len;
>>> char __user *uinsns;
>>> - u32 ulen;
>>> + u32 ulen, i;
>>> int err;
>>>
>>> err = check_uarg_tail_zero(uinfo, sizeof(info), info_len);
>>> @@ -1922,7 +1922,6 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog
>>> *prog,
>>> ulen = min_t(u32, info.nr_map_ids, ulen);
>>> if (ulen) {
>>> u32 __user *user_map_ids = u64_to_user_ptr(info.map_ids);
>>> - u32 i;
>>>
>>> for (i = 0; i < ulen; i++)
>>> if (put_user(prog->aux->used_maps[i]->id,
>>> @@ -1970,13 +1969,41 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog
>>> *prog,
>>> * for offload.
>>> */
>>> ulen = info.jited_prog_len;
>>> - info.jited_prog_len = prog->jited_len;
>>> + if (prog->aux->func_cnt) {
>>> + info.jited_prog_len = 0;
>>> + for (i = 0; i < prog->aux->func_cnt; i++)
>>> + info.jited_prog_len += prog->aux->func[i]->jited_len;
>>> + } else {
>>> + info.jited_prog_len = prog->jited_len;
>>> + }
>>> +
>>> if (info.jited_prog_len && ulen) {
>>> if (bpf_dump_raw_ok()) {
>>> uinsns = u64_to_user_ptr(info.jited_prog_insns);
>>> ulen = min_t(u32, info.jited_prog_len, ulen);
>>> - if (copy_to_user(uinsns, prog->bpf_func, ulen))
>>> - return -EFAULT;
>>> +
>>> + /* for multi-function programs, copy the JITed
>>> + * instructions for all the functions
>>> + */
>>> + if (prog->aux->func_cnt) {
>>> + u32 len, free;
>>> + u8 *img;
>>> +
>>> + free = ulen;
>>> + for (i = 0; i < prog->aux->func_cnt; i++) {
>>> + len = prog->aux->func[i]->jited_len;
>>> + img = (u8 *)
>>> prog->aux->func[i]->bpf_func;
>>> + if (len > free)
>>> + break;
>>> + if (copy_to_user(uinsns, img, len))
>>> + return -EFAULT;
>>> + uinsns += len;
>>> + free -= len;
>>
>> Is there any way we can introduce a delimiter between the different
>> images such that they could be more easily correlated with the call
>> from the main (or other sub-)program instead of having one contiguous
>> dump blob?
>
> Can we have another member in bpf_prog_info that points to a list of the
> lengths of the
> JITed images for each subprogram? We can use this information to split up the
> dump.
Seems okay to me.
Thanks,
Daniel
