Hi On Thu, 26 Dec 2019 11:57:07 +0900 Masami Hiramatsu wrote: > > Hi Jisheng, > > On Wed, 25 Dec 2019 09:44:21 +0000 > Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote: > > > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > > eliminates the need for a trap, as well as the need to emulate or > > single-step instructions. > > > > Tested on berlin arm64 platform. > > > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > > ~ # cd /sys/kernel/debug/ > > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > > > before the patch: > > > > /sys/kernel/debug # cat kprobes/list > > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > > > after the patch: > > > > /sys/kernel/debug # cat kprobes/list > > ffffff801009ff54 k _do_fork+0x0 [DISABLED][FTRACE] > > What happens if user puts a probe on _do_fork+4? > Is that return -EILSEQ correctly? _do_fork+4 can be probed successfully. > > > > > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> > > --- > > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- > > arch/arm64/Kconfig | 1 + > > arch/arm64/include/asm/ftrace.h | 1 + > > arch/arm64/kernel/probes/Makefile | 1 + > > arch/arm64/kernel/probes/ftrace.c | 78 +++++++++++++++++++ > > 5 files changed, 82 insertions(+), 1 deletion(-) > > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > > > diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > index 4fae0464ddff..f9dd9dd91e0c 100644 > > --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > @@ -9,7 +9,7 @@ > > | alpha: | TODO | > > | arc: | TODO | > > | arm: | TODO | > > - | arm64: | TODO | > > + | arm64: | ok | > > | c6x: | TODO | > > | csky: | TODO | > > | h8300: | TODO | > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index b1b4476ddb83..92b9882889ac 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -166,6 +166,7 @@ config ARM64 > > select HAVE_STACKPROTECTOR > > select HAVE_SYSCALL_TRACEPOINTS > > select HAVE_KPROBES > > + select HAVE_KPROBES_ON_FTRACE > > select HAVE_KRETPROBES > > select HAVE_GENERIC_VDSO > > select IOMMU_DMA if IOMMU_SUPPORT > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > index 91fa4baa1a93..875aeb839654 100644 > > --- a/arch/arm64/include/asm/ftrace.h > > +++ b/arch/arm64/include/asm/ftrace.h > > @@ -20,6 +20,7 @@ > > > > /* The BL at the callsite's adjusted rec->ip */ > > #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE > > +#define FTRACE_IP_EXTENSION MCOUNT_INSN_SIZE > > > > #define FTRACE_PLT_IDX 0 > > #define FTRACE_REGS_PLT_IDX 1 > > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > > index 8e4be92e25b1..4020cfc66564 100644 > > --- a/arch/arm64/kernel/probes/Makefile > > +++ b/arch/arm64/kernel/probes/Makefile > > @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > > simulate-insn.o > > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > > simulate-insn.o > > +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o > > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c > > new file mode 100644 > > index 000000000000..0643aa2dacdb > > --- /dev/null > > +++ b/arch/arm64/kernel/probes/ftrace.c > > @@ -0,0 +1,78 @@ > > +// SPDX-License-Identifier: GPL-2.0-or-later > > +/* > > + * Dynamic Ftrace based Kprobes Optimization > > + * > > + * Copyright (C) Hitachi Ltd., 2012 > > + * Copyright (C) 2019 Jisheng Zhang <jszhang@xxxxxxxxxx> > > + * Synaptics Incorporated > > + */ > > + > > +#include <linux/kprobes.h> > > + > > +/* > > + * In arm64 FTRACE_WITH_REGS implementation, we patch two nop instructions: > > + * the lr saver and bl ftrace-entry. Both these instructions are claimed > > + * by ftrace and we should allow probing on either instruction. > > No, the 2nd bl ftrace-entry must not be probed. > The pair of lr-saver and bl ftrace-entry is tightly coupled. You can not > decouple it. This is the key. different viewing of this results in different implementation. I'm just wondering why are the two instructions considered as coupled. I think here we met similar situation as powerpc: https://lkml.org/lkml/2019/6/18/646 the "mflr r0" equals to lr-saver here, branch to _mcount equals to bl ftrace-entry could you please kindly comment more? Thanks in advance > > > + */ > > +int arch_check_ftrace_location(struct kprobe *p) > > +{ > > + if (ftrace_location((unsigned long)p->addr)) > > + p->flags |= KPROBE_FLAG_FTRACE; > > + return 0; > > +} > > Thus, this must return -EILSEQ if user puts a probe on the bl. > > > + > > +/* Ftrace callback handler for kprobes -- called under preepmt disabed */ > > +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > + struct ftrace_ops *ops, struct pt_regs *regs) > > +{ > > + bool lr_saver = false; > > + struct kprobe *p; > > + struct kprobe_ctlblk *kcb; > > + > > + /* Preempt is disabled by ftrace */ > > + p = get_kprobe((kprobe_opcode_t *)ip); > > + if (!p) { > > + p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE)); > > + if (unlikely(!p) || kprobe_disabled(p)) > > + return; > > + lr_saver = true; > > Then, this can be removed. > > > + } > > + > > + kcb = get_kprobe_ctlblk(); > > + if (kprobe_running()) { > > + kprobes_inc_nmissed_count(p); > > + } else { > > + unsigned long orig_ip = instruction_pointer(regs); > > + > > + if (lr_saver) > > + ip -= MCOUNT_INSN_SIZE; > > Ditto. > > Thank you, > > > + instruction_pointer_set(regs, ip); > > + __this_cpu_write(current_kprobe, p); > > + kcb->kprobe_status = KPROBE_HIT_ACTIVE; > > + if (!p->pre_handler || !p->pre_handler(p, regs)) { > > + /* > > + * Emulate singlestep (and also recover regs->pc) > > + * as if there is a nop > > + */ > > + instruction_pointer_set(regs, > > + (unsigned long)p->addr + MCOUNT_INSN_SIZE); > > + if (unlikely(p->post_handler)) { > > + kcb->kprobe_status = KPROBE_HIT_SSDONE; > > + p->post_handler(p, regs, 0); > > + } > > + instruction_pointer_set(regs, orig_ip); > > + } > > + /* > > + * If pre_handler returns !0, it changes regs->pc. We have to > > + * skip emulating post_handler. > > + */ > > + __this_cpu_write(current_kprobe, NULL); > > + } > > +} > > +NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > + > > +int arch_prepare_kprobe_ftrace(struct kprobe *p) > > +{ > > + p->ainsn.api.insn = NULL; > > + return 0; > > +} > > -- > > 2.24.1 > > > > > -- > Masami Hiramatsu <mhiramat@xxxxxxxxxx>
