Re: [PATCH ftrace/core 0/2] ftrace, kprobes: Introduce IPMODIFY flag for ftrace_ops to detect conflicts

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Tue, Jun 10, 2014 at 10:50:01AM +0000, Masami Hiramatsu wrote:
> Hi,
> 
> Here is a pair of patches which introduces IPMODIFY flag for
> ftrace_ops to detect conflicts of ftrace users who can modify
> regs->ip in their handler.
> Currently, only kprobes can change the regs->ip in the handler,
> but recently kpatch is also want to change it. Moreover, since
> the ftrace itself exported to modules, it might be considerable
> senario.
> 
> Here we talked on github.
>  https://github.com/dynup/kpatch/issues/47
> 
> To protect modified regs-ip from each other, this series
> introduces FTRACE_OPS_FL_IPMODIFY flag and ftrace now ensures
> the flag can be set on each function entry location. If there
> is someone who already reserve regs->ip on target function
> entry, ftrace_set_filter_ip or register_ftrace_function will
> return -EBUSY. Users must handle that.
> 
> At this point, all kprobes will reserve regs->ip, since jprobe
> requires it.

Masami, thanks very much for this!

One issue with this approach is that it _always_ makes kprobes and
kpatch incompatible when probing/patching the same function, even when
kprobes doesn't need to touch regs->ip.

Is it possible to add a kprobes flag (KPROBE_FLAG_IPMODIFY), which is
only set by those kprobes users (just jprobes?) which need to modify IP?
Then kprobes could only set the corresponding ftrace flag when it's
really needed.  And I think kprobes could even enforce the fact that
!KPROBE_FLAG_IPMODIFY users don't change regs->ip.


BTW, I've done some testing with this patch set by patching/probing the
same function with FTRACE_OPS_FL_IPMODIFY, and got some warnings.  I saw
the following warning when attempting to kpatch a kprobed function:


  WARNING: CPU: 2 PID: 18351 at kernel/trace/ftrace.c:419 __unregister_ftrace_function+0x1be/0x1d0()
  Modules linked in: kpatch_meminfo_string(OE+) kpatch(OE) stap_8d70d6e041605bd1e144cba4801652_14636(OE) rfcomm fuse ipt_MASQUERADE ccm xt_CHECKSUM tun ip6t_rpfilter ip6t_REJECT xt_conntrack bnep ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw arc4 iwldvm mac80211 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic x86_pkg_temp_thermal coretemp kvm_intel snd_hda_intel iTCO_wdt iTCO_vendor_support snd_hda_controller kvm snd_hda_codec iwlwifi snd_hwdep uvcvideo snd_seq videobuf2_vmalloc videobuf2_memops snd_seq_device
   videobuf2_core btusb v4l2_common snd_pcm videodev nfsd cfg80211 microcode e1000e bluetooth media thinkpad_acpi joydev sdhci_pci sdhci pcspkr serio_raw snd_timer i2c_i801 snd mmc_core auth_rpcgss mei_me mei lpc_ich mfd_core shpchp ptp pps_core wmi tpm_tis soundcore tpm rfkill nfs_acl lockd sunrpc dm_crypt i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel i2c_core video
  CPU: 2 PID: 18351 Comm: insmod Tainted: G        W  OE 3.15.0-IPMODIFY+ #1
  Hardware name: LENOVO 2356BH8/2356BH8, BIOS G7ET63WW (2.05 ) 11/12/2012
   0000000000000000 00000000b39bd289 ffff8803b78d7bc0 ffffffff816f31ed
   0000000000000000 ffff8803b78d7bf8 ffffffff8108914d ffffffffa07f9040
   00000000fffffff0 0000000000000000 0000000000000001 ffff8803e7ac4200
  Call Trace:
   [<ffffffff816f31ed>] dump_stack+0x45/0x56
   [<ffffffff8108914d>] warn_slowpath_common+0x7d/0xa0
   [<ffffffff8108927a>] warn_slowpath_null+0x1a/0x20
   [<ffffffff81135bae>] __unregister_ftrace_function+0x1be/0x1d0
   [<ffffffff81137294>] ftrace_startup+0x1e4/0x220
   [<ffffffff81137313>] register_ftrace_function+0x43/0x60
   [<ffffffffa07f6c84>] kpatch_register+0x664/0x830 [kpatch]
   [<ffffffffa0810000>] ? 0xffffffffa080ffff
   [<ffffffffa0810000>] ? 0xffffffffa080ffff
   [<ffffffffa0046194>] patch_init+0x194/0x1000 [kpatch_meminfo_string]
   [<ffffffffa0046000>] ? 0xffffffffa0045fff
   [<ffffffff81002144>] do_one_initcall+0xd4/0x210
   [<ffffffff81059d43>] ? set_memory_nx+0x43/0x50
   [<ffffffff81102e42>] load_module+0x1d92/0x25e0
   [<ffffffff810feb60>] ? store_uevent+0x70/0x70
   [<ffffffff811eba30>] ? kernel_read+0x50/0x80
   [<ffffffff81103846>] SyS_finit_module+0xa6/0xd0
   [<ffffffff81703179>] system_call_fastpath+0x16/0x1b


That warning happened because __unregister_ftrace_function() doesn't
expect FTRACE_OPS_FL_ENABLED to be cleared in the ftrace_startup error
path.  I tried removing the FTRACE_OPS_FL_ENABLED clearing line in
ftrace_startup, but I saw more warnings.  This one happened when
attempting to kprobe a kpatched function:


  WARNING: CPU: 3 PID: 4444 at kernel/kprobes.c:953 arm_kprobe+0xa7/0xe0()
  Failed to init kprobe-ftrace (-16)
  Modules linked in: stap_b2ea0de23f179d8ded86fcc19fcc533_4444(OE) kpatch_meminfo_string(OE) kpatch(OE) rfcomm fuse ccm ipt_MASQUERADE xt_CHECKSUM tun ip6t_rpfilter ip6t_REJECT xt_conntrack bnep ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw arc4 iwldvm mac80211 iTCO_wdt iTCO_vendor_support x86_pkg_temp_thermal coretemp kvm_intel kvm snd_hda_codec_hdmi iwlwifi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_seq uvcvideo btusb cfg80211 bluetooth videobuf2_vmalloc videobuf2_memops
   videobuf2_core v4l2_common videodev snd_seq_device snd_pcm sdhci_pci media sdhci joydev nfsd i2c_i801 serio_raw pcspkr mmc_core microcode snd_timer e1000e lpc_ich thinkpad_acpi mfd_core shpchp snd wmi tpm_tis soundcore tpm ptp rfkill mei_me auth_rpcgss mei pps_core nfs_acl lockd sunrpc dm_crypt i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel i2c_core video [last unloaded: kpatch_meminfo_string]
  CPU: 3 PID: 4444 Comm: stapio Tainted: G     U  W  OE 3.15.0-IPMODIFY+ #1
  Hardware name: LENOVO 2356BH8/2356BH8, BIOS G7ET63WW (2.05 ) 11/12/2012
   0000000000000000 000000009cd22363 ffff880427bdfd80 ffffffff816f31ed
   ffff880427bdfdc8 ffff880427bdfdb8 ffffffff8108914d ffffffffa08258e0
   ffffffffa08258f0 0000000000000000 0000000000000000 0000000000000000
  Call Trace:
   [<ffffffff816f31ed>] dump_stack+0x45/0x56
   [<ffffffff8108914d>] warn_slowpath_common+0x7d/0xa0
   [<ffffffff810891cc>] warn_slowpath_fmt+0x5c/0x80
   [<ffffffff816ff9d7>] arm_kprobe+0xa7/0xe0
   [<ffffffff817007f7>] register_kprobe+0x557/0x5d0
   [<ffffffff81254da0>] ? meminfo_proc_open+0x30/0x30
   [<ffffffffa0820c95>] _stp_ctl_write_cmd+0x8d5/0x930 [stap_b2ea0de23f179d8ded86fcc19fcc533_4444]
   [<ffffffff811e5daa>] vfs_write+0xba/0x1e0
   [<ffffffff811e6965>] SyS_write+0x55/0xd0
   [<ffffffff81703179>] system_call_fastpath+0x16/0x1b


And this one happened after unregistering a probe and then attempting to
register kpatch:


  WARNING: CPU: 1 PID: 18041 at kernel/trace/ftrace.c:1584 __ftrace_hash_rec_update.part.35+0x20a/0x240()
  Modules linked in: kpatch_meminfo_string(OE+) kpatch(OE) rfcomm fuse ipt_MASQUERADE ccm xt_CHECKSUM tun ip6t_rpfilter ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge bnep stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw arc4 iwldvm iTCO_wdt iTCO_vendor_support mac80211 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_hda_controller x86_pkg_temp_thermal snd_hda_codec coretemp iwlwifi kvm_intel kvm snd_hwdep snd_seq cfg80211 snd_seq_device uvcvideo btusb videobuf2_vmalloc snd_pcm videobuf2_memops videobuf2_core v4l2_common
   videodev microcode bluetooth media e1000e pcspkr snd_timer sdhci_pci sdhci thinkpad_acpi i2c_i801 joydev snd serio_raw mmc_core lpc_ich ptp mei_me mfd_core pps_core mei shpchp soundcore rfkill tpm_tis wmi tpm nfsd auth_rpcgss nfs_acl lockd sunrpc dm_crypt i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel i2c_core video [last unloaded: stap_bc293456f85bd78c424ce27a4ab459_18005]
  CPU: 1 PID: 18041 Comm: insmod Tainted: G        W  OE 3.15.0-IPMODIFY+ #1
  Hardware name: LENOVO 2356BH8/2356BH8, BIOS G7ET63WW (2.05 ) 11/12/2012
   ffff8803b4717ad8 00000000af73dd79 ffff8803b4717ae8 ffffffff816f31ed
   0000000000000000 ffff8803b4717b20 ffffffff8108914d 0000000000000000
   0000000000000001 ffff8804280a0ea0 00000000000020ea ffff88042dc04aa0
  Call Trace:
   [<ffffffff816f31ed>] dump_stack+0x45/0x56
   [<ffffffff8108914d>] warn_slowpath_common+0x7d/0xa0
   [<ffffffff8108927a>] warn_slowpath_null+0x1a/0x20
   [<ffffffff811359ba>] __ftrace_hash_rec_update.part.35+0x20a/0x240
   [<ffffffff81135e25>] ftrace_hash_move+0x1d5/0x200
   [<ffffffff81137e16>] ftrace_set_hash+0x126/0x1d0
   [<ffffffff81254da0>] ? meminfo_proc_open+0x30/0x30
   [<ffffffff81254da0>] ? meminfo_proc_open+0x30/0x30
   [<ffffffff81137f20>] ftrace_set_filter_ip+0x60/0x70
   [<ffffffffa07efa50>] kpatch_register+0x430/0x830 [kpatch]
   [<ffffffffa0809000>] ? 0xffffffffa0808fff
   [<ffffffffa0809000>] ? 0xffffffffa0808fff
   [<ffffffffa0047194>] patch_init+0x194/0x1000 [kpatch_meminfo_string]
   [<ffffffffa0047000>] ? 0xffffffffa0046fff
   [<ffffffff81002144>] do_one_initcall+0xd4/0x210
   [<ffffffffa0047000>] ? 0xffffffffa0046fff
   [<ffffffff81102e42>] load_module+0x1d92/0x25e0
   [<ffffffff810feb60>] ? store_uevent+0x70/0x70
   [<ffffffff811eba30>] ? kernel_read+0x50/0x80
   [<ffffffff81103846>] SyS_finit_module+0xa6/0xd0
   [<ffffffff81703179>] system_call_fastpath+0x16/0x1b


-- 
Josh