Hi Daniel,
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.
- Sandipan
>> + }
>> + } else {
>> + if (copy_to_user(uinsns, prog->bpf_func, ulen))
>> + return -EFAULT;
>> + }
>> } else {
>> info.jited_prog_insns = 0;
>> }
>> @@ -1987,7 +2014,6 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog
>> *prog,
>> if (info.nr_jited_ksyms && ulen) {
>> u64 __user *user_jited_ksyms =
>> u64_to_user_ptr(info.jited_ksyms);
>> ulong ksym_addr;
>> - u32 i;
>>
>> /* copy the address of the kernel symbol corresponding to
>> * each function
>>
>
>
