On Tue, 22 May 2018 22:46:10 +0530, 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
> ...
>
> # 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 | 36 +++++++++++++++++++++++++++++++++---
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index f0ad4b5f0224..1c4cba91e523 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1970,13 +1970,43 @@ 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) {
> + u32 i;
> +
> + 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, i;
> + 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;
nit: interesting, the previous code used to fill up the space
completely, I would personally vote to keep that behaviour and do:
len = min(len, free);
copy();
free -= len;
if (!free)
break;
otherwise the user space doesn't know when to stop disassembling
truncated output. But that's really a corner case, so not sure we care.
> + if (copy_to_user(uinsns, img, len))
> + return -EFAULT;
> + uinsns += len;
> + free -= len;
> + }
> + } else {
> + if (copy_to_user(uinsns, prog->bpf_func, ulen))
> + return -EFAULT;
> + }
> } else {
> info.jited_prog_insns = 0;
> }
