Re: [PATCH net-next 3/3] bpf: make jited programs visible in traces
From: Eric Dumazet <hidden>
Date: 2017-02-20 19:05:41
Also in:
lkml
On Thu, 2017-02-16 at 22:24 +0100, Daniel Borkmann wrote:
Long standing issue with JITed programs is that stack traces from
function tracing check whether a given address is kernel code
through {__,}kernel_text_address(), which checks for code in core
kernel, modules and dynamically allocated ftrace trampolines. But
what is still missing is BPF JITed programs (interpreted programs
are not an issue as __bpf_prog_run() will be attributed to them),
thus when a stack trace is triggered, the code walking the stack
won't see any of the JITed ones. The same for address correlation
done from user space via reading /proc/kallsyms. This is read by
tools like perf, but the latter is also useful for permanent live
tracing with eBPF itself in combination with stack maps when other
eBPF types are part of the callchain. See offwaketime example on
dumping stack from a map.
This work tries to tackle that issue by making the addresses and
symbols known to the kernel. The lookup from *kernel_text_address()
is implemented through a latched RB tree that can be read under
RCU in fast-path that is also shared for symbol/size/offset lookup
for a specific given address in kallsyms. The slow-path iteration
through all symbols in the seq file done via RCU list, which holds
a tiny fraction of all exported ksyms, usually below 0.1 percent.
Function symbols are exported as bpf_prog_<tag>, in order to aide
debugging and attribution. This facility is currently enabled for
root-only when bpf_jit_kallsyms is set to 1, and disabled if hardening
is active in any mode. The rationale behind this is that still a lot
of systems ship with world read permissions on kallsyms thus addresses
should not get suddenly exposed for them. If that situation gets
much better in future, we always have the option to change the
default on this. Likewise, unprivileged programs are not allowed
to add entries there either, but that is less of a concern as most
such programs types relevant in this context are for root-only anyway.
If enabled, call graphs and stack traces will then show a correct
attribution; one example is illustrated below, where the trace is
now visible in tooling such as perf script --kallsyms=/proc/kallsyms
and friends.
Before:
7fff8166889d bpf_clone_redirect+0x80007f0020ed (/lib/modules/4.9.0-rc8+/build/vmlinux)
f5d80 __sendmsg_nocancel+0xffff006451f1a007 (/usr/lib64/libc-2.18.so)
After:
7fff816688b7 bpf_clone_redirect+0x80007f002107 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fffa0575728 bpf_prog_33c45a467c9e061a+0x8000600020fb (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fffa07ef1fc cls_bpf_classify+0x8000600020dc (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff81678b68 tc_classify+0x80007f002078 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8164d40b __netif_receive_skb_core+0x80007f0025fb (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8164d718 __netif_receive_skb+0x80007f002018 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8164e565 process_backlog+0x80007f002095 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8164dc71 net_rx_action+0x80007f002231 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff81767461 __softirqentry_text_start+0x80007f0020d1 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff817658ac do_softirq_own_stack+0x80007f00201c (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff810a2c20 do_softirq+0x80007f002050 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff810a2cb5 __local_bh_enable_ip+0x80007f002085 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8168d452 ip_finish_output2+0x80007f002152 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8168ea3d ip_finish_output+0x80007f00217d (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff8168f2af ip_output+0x80007f00203f (/lib/modules/4.9.0-rc8+/build/vmlinux)
[...]
7fff81005854 do_syscall_64+0x80007f002054 (/lib/modules/4.9.0-rc8+/build/vmlinux)
7fff817649eb return_from_SYSCALL_64+0x80007f002000 (/lib/modules/4.9.0-rc8+/build/vmlinux)
f5d80 __sendmsg_nocancel+0xffff01c484812007 (/usr/lib64/libc-2.18.so)
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: linux-kernel@vger.kernel.org
---Latest net-next tree dies on my hosts, and my bisection came to this commit. [ 90.045546] BUG: unable to handle kernel paging request at ffff881fef01a000^M [ 90.052535] IP: __tlb_remove_page_size+0x57/0x90^M [ 90.057152] PGD 2247067 ^M [ 90.057153] PUD 1fdaadc063 ^M [ 90.059691] PMD 1fefb0b063 ^M [ 90.062491] PTE 8000001fef01a161^M [ 90.065287] ^M [ 90.070011] Oops: 0003 [#1] SMP^M [ 90.073478] gsmi: Log Shutdown Reason 0x03^M [ 90.077584] Modules linked in: w1_therm wire cdc_acm ehci_pci ehci_hcd mlx4_en ib_uverbs mlx4_ib ib_core mlx4_core^M [ 90.087972] CPU: 34 PID: 9747 Comm: sshd Not tainted 4.10.0-smp-DEV #14^M [ 90.101580] task: ffff881fda56a300 task.stack: ffffc900337d4000^M [ 90.107515] RIP: 0010:__tlb_remove_page_size+0x57/0x90^M [ 90.112651] RSP: 0018:ffffc900337d7c98 EFLAGS: 00010202^M [ 90.117896] RAX: ffff881fef01a000 RBX: ffffc900337d7df8 RCX: 0000000000000001^M [ 90.125086] RDX: ffff880000000000 RSI: 0000000000000011 RDI: ffff88207fffe4c0^M [ 90.132234] RBP: ffffc900337d7ca0 R08: 0000000000000010 R09: ffffc900337d7bd8^M [ 90.139371] R10: 0000000000000020 R11: 0000000000000001 R12: ffff881fda064520^M [ 90.146544] R13: ffffea00ffb28f40 R14: 00007f84584a5000 R15: ffffc900337d7df8^M [ 90.153703] FS: 0000000000000000(0000) GS:ffff881fffd80000(0000) knlGS:0000000000000000^M [ 90.161802] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M [ 90.167548] CR2: ffff881fef01a000 CR3: 0000000001c09000 CR4: 00000000001406e0^M [ 90.174680] Call Trace:^M [ 90.177144] unmap_page_range+0x679/0x840^M [ 90.181154] unmap_single_vma+0x7f/0xf0^M [ 90.184984] unmap_vmas+0x4a/0xa0^M [ 90.188292] exit_mmap+0xa2/0x160^M [ 90.191605] mmput+0x3d/0x100^M[ 90.194584] do_exit+0x325/0xbc0^M [ 90.197810] ? vfs_read+0x95/0x140^M [ 90.201230] do_group_exit+0x49/0xc0^M [ 90.204818] SyS_exit_group+0x14/0x20^M [ 90.208492] entry_SYSCALL_64_fastpath+0x13/0x94^M [ 90.213127] RIP: 0033:0x7f8457b10279^M [ 90.216723] RSP: 002b:00007ffef283a8f0 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7^M [ 90.224286] RAX: ffffffffffffffda RBX: 000055692c599640 RCX: 00007f8457b10279^M [ 90.231432] RDX: 0000000000000000 RSI: 00000000000000ff RDI: 00000000000000ff^M [ 90.238575] RBP: 00007ffef283a9f0 R08: 000000000000003c R09: 00000000000000e7^M [ 90.245728] R10: ffffffffffffff90 R11: 0000000000000246 R12: 000055692c599640^M [ 90.252875] R13: 0000000000002614 R14: 000000000000ac60 R15: 00007ffef283aa90^M [ 90.260018] Code: 89 47 20 31 c0 c3 83 7f 78 13 74 45 55 53 31 f6 48 89 fb bf 00 02 00 01 48 8d 6c 24 08 e8 c2 05 fd ff 48 85 c0 74 30 83 43 78 01 <48> c7 00 00 00 00 00 c7 40 08 00 00 00 00 c7 40 0c fe 01 00 00 ^M [ 90.278939] RIP: __tlb_remove_page_size+0x57/0x90 RSP: ffffc900337d7c98^M [ 90.285550] CR2: ffff881fef01a000^M