Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755849AbaFLMut (ORCPT ); Thu, 12 Jun 2014 08:50:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41243 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752781AbaFLMur (ORCPT ); Thu, 12 Jun 2014 08:50:47 -0400 Date: Thu, 12 Jun 2014 07:50:34 -0500 From: Josh Poimboeuf To: Namhyung Kim Cc: Masami Hiramatsu , Steven Rostedt , Ingo Molnar , Linux Kernel Mailing List , Ananth N Mavinakayanahalli Subject: Re: [PATCH ftrace/core 0/2] ftrace, kprobes: Introduce IPMODIFY flag for ftrace_ops to detect conflicts Message-ID: <20140612125034.GB3863@treble.redhat.com> References: <20140610105001.8732.93502.stgit@kbuild-fedora.novalocal> <20140611165826.GA5087@treble.redhat.com> <87d2eeajre.fsf@sejong.aot.lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87d2eeajre.fsf@sejong.aot.lge.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 12, 2014 at 12:28:53PM +0900, Namhyung Kim wrote: > Hi Josh, > > On Wed, 11 Jun 2014 11:58:26 -0500, Josh Poimboeuf wrote: > > 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_dev > > ice > > 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: > > [] dump_stack+0x45/0x56 > > [] warn_slowpath_common+0x7d/0xa0 > > [] warn_slowpath_null+0x1a/0x20 > > [] __unregister_ftrace_function+0x1be/0x1d0 > > [] ftrace_startup+0x1e4/0x220 > > [] register_ftrace_function+0x43/0x60 > > [] kpatch_register+0x664/0x830 [kpatch] > > [] ? 0xffffffffa080ffff > > [] ? 0xffffffffa080ffff > > [] patch_init+0x194/0x1000 [kpatch_meminfo_string] > > [] ? 0xffffffffa0045fff > > [] do_one_initcall+0xd4/0x210 > > [] ? set_memory_nx+0x43/0x50 > > [] load_module+0x1d92/0x25e0 > > [] ? store_uevent+0x70/0x70 > > [] ? kernel_read+0x50/0x80 > > [] SyS_finit_module+0xa6/0xd0 > > [] 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. > > Did you just remove the clearing line or actually clear the flag after > __unregister_ftrace_function() was called? Ah, I just removed the clearing line. Looks like I should have also cleared it after calling __unregister_ftrace_function(). > > > > 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 vide > > obuf2_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: > > [] dump_stack+0x45/0x56 > > [] warn_slowpath_common+0x7d/0xa0 > > [] warn_slowpath_fmt+0x5c/0x80 > > [] arm_kprobe+0xa7/0xe0 > > [] register_kprobe+0x557/0x5d0 > > [] ? meminfo_proc_open+0x30/0x30 > > [] _stp_ctl_write_cmd+0x8d5/0x930 [stap_b2ea0de23f179d8ded86fcc19fcc533_4444] > > [] vfs_write+0xba/0x1e0 > > [] SyS_write+0x55/0xd0 > > [] system_call_fastpath+0x16/0x1b > > This one looks fairly normal as kpatch set FTRACE_FL_IPMODIFY and kprobe > see it again.. Instead of a warning I'd expect to see register_kprobe return an error back to stap. > > > > > > > > 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: > > [] dump_stack+0x45/0x56 > > [] warn_slowpath_common+0x7d/0xa0 > > [] warn_slowpath_null+0x1a/0x20 > > [] __ftrace_hash_rec_update.part.35+0x20a/0x240 > > [] ftrace_hash_move+0x1d5/0x200 > > [] ftrace_set_hash+0x126/0x1d0 > > [] ? meminfo_proc_open+0x30/0x30 > > [] ? meminfo_proc_open+0x30/0x30 > > [] ftrace_set_filter_ip+0x60/0x70 > > [] kpatch_register+0x430/0x830 [kpatch] > > [] ? 0xffffffffa0808fff > > [] ? 0xffffffffa0808fff > > [] patch_init+0x194/0x1000 [kpatch_meminfo_string] > > [] ? 0xffffffffa0046fff > > [] do_one_initcall+0xd4/0x210 > > [] ? 0xffffffffa0046fff > > [] load_module+0x1d92/0x25e0 > > [] ? store_uevent+0x70/0x70 > > [] ? kernel_read+0x50/0x80 > > [] SyS_finit_module+0xa6/0xd0 > > [] system_call_fastpath+0x16/0x1b > > But this is weird since kpatch_register() calls ftrace_set_filter_ip() > before registering kpatch_ftrace_ops. So the ops->flags should not have > FTRACE_OPS_FL_ENABLED and it makes __ftrace_hash_rec_update() return > immediately. > > So I guessed a following scenario: > > register kprobe (success) > register kpatch (-EBUSY, but not reset _FL_ENABLED) > unregister kprobe (success) > register kpatch (boom...) That's entirely possible :-) -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/