Messages in this thread | | | From | Jianhua Liu <> | Date | Fri, 7 Jan 2022 01:34:16 +0800 | Subject | Re: [PATCH v2 2/2] arm64: kprobes: add support for KPROBES_ON_FTRACE |
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On Fri, Dec 17, 2021 at 3:40 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > Hi, > > On Tue, 2 Nov 2021 21:11:46 +0800 > Janet Liu <jianhua.ljh@gmail.com> wrote: > > > From: Janet Liu <janet.liu@unisoc.com> > > > > This patch allow kprobes on ftrace call sites. This optimization > > avoids use of a trap with regular kprobes. > > > > This depends on HAVE_DYNAMIC_FTRACE_WITH_REGS which depends on > > "patchable-function-entry" options which is only implemented with newer > > toolchains. > > > > Signed-off-by: Janet Liu <janet.liu@unisoc.com> > > --- > > arch/arm64/Kconfig | 1 + > > arch/arm64/kernel/probes/Makefile | 1 + > > arch/arm64/kernel/probes/ftrace.c | 73 ++++++++++++++++++++++++++++++ > > arch/arm64/kernel/probes/kprobes.c | 27 +++++++++++ > > 4 files changed, 102 insertions(+) > > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 339130712093..f59005608976 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -200,6 +200,7 @@ config ARM64 > > select HAVE_SYSCALL_TRACEPOINTS > > select HAVE_KPROBES > > select HAVE_OPTPROBES > > + select HAVE_KPROBES_ON_FTRACE > > select HAVE_KRETPROBES > > select HAVE_GENERIC_VDSO > > select IOMMU_DMA if IOMMU_SUPPORT > > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > > index c77c92ac95fd..d9b204f4795a 100644 > > --- a/arch/arm64/kernel/probes/Makefile > > +++ b/arch/arm64/kernel/probes/Makefile > > @@ -3,5 +3,6 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > > kprobes_trampoline.o \ > > simulate-insn.o > > obj-$(CONFIG_OPTPROBES) += opt.o opt_head.o > > +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o > > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > > simulate-insn.o > > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c > > new file mode 100644 > > index 000000000000..46ea92eb552f > > --- /dev/null > > +++ b/arch/arm64/kernel/probes/ftrace.c > > @@ -0,0 +1,73 @@ > > +// SPDX-License-Identifier: GPL-2.0-only > > +// > > +// Dynamic Ftrace based Kprobes Optimization > > +// > > +// Copyright (C) 2021, Unisoc Inc. > > +// Author: Janet Liu <janet.liu@unisoc.com> > > +#include <linux/kprobes.h> > > +#include <linux/ptrace.h> > > +#include <linux/hardirq.h> > > +#include <linux/preempt.h> > > +#include <linux/ftrace.h> > > + > > + > > +/* Ftrace callback handler for kprobes*/ > > +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > + struct ftrace_ops *ops, struct ftrace_regs *fregs) > > +{ > > + struct kprobe *p; > > + struct kprobe_ctlblk *kcb; > > + struct pt_regs *regs = ftrace_get_regs(fregs); > > + int bit; > > + > > + bit = ftrace_test_recursion_trylock(ip, parent_ip); > > + if (bit < 0) > > + return; > > + > > + preempt_disable_notrace(); > > This already has been done in ftrace side.
Hi Masami,
Got it by reading code, will fix this.
> > > + p = get_kprobe((kprobe_opcode_t *)ip); > > + if (unlikely(!p) || kprobe_disabled(p)) > > + goto end; > > + > > + kcb = get_kprobe_ctlblk(); > > + if (kprobe_running()) { > > + kprobes_inc_nmissed_count(p); > > + } else { > > + unsigned long orig_ip = instruction_pointer(regs); > > + > > + instruction_pointer_set(regs, ip); > > The 'ip' is the address of the 'bl' instruction, which must be > p->addr + AARCH64_INSN_SIZE * 2. But this is a bit strange. > > On aarch64, if the user probe callback is called from breakpoint handler, > regs->pc == kp->addr. But in this case, it is not the same. > > So, what about this? > > instruction_pointer_set(regs, ip - AARCH64_INSN_SIZE); >
I got what you said.
But p->addr is changed when KPROBES_ON_FTRACE enable. I implemented kprobe_lookup_name for arm64 to do the change in this patch. because kernel/kprobe.c:check_ftrace_location check, if p->addr != ftrace_addr, don't kprobe on ftrace entry. so p->addr is equal to ftrace addr(the second nop), is equal to 'ip'. here should be 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); > > And then, this will be > > instruction_pointer_set(regs, > (unsigned long)p->addr + AARCH64_INSN_SIZE * 2); > > So basically, kprobes on ftrace will skips 2 NOP instructions (the compiler installed > 2 nops) and call post handler. This means we have a virtual big NOP instruction there. > Ditto, skip two nop instructions should instruction_pointer_set(regs, (unsigned long)p->addr + AARCH64_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); > > + } > > +end: > > + preempt_enable_notrace(); > > + ftrace_test_recursion_unlock(bit); > > +} > > +NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > + > > +int arch_prepare_kprobe_ftrace(struct kprobe *p) > > +{ > > + p->ainsn.api.insn = NULL; > > + p->ainsn.api.restore = 0; > > + return 0; > > +} > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > > index 6dbcc89f6662..3d371d3e4dfa 100644 > > --- a/arch/arm64/kernel/probes/kprobes.c > > +++ b/arch/arm64/kernel/probes/kprobes.c > > @@ -417,6 +417,33 @@ int __kprobes arch_trampoline_kprobe(struct kprobe *p) > > return 0; > > } > > > > +kprobe_opcode_t __kprobes *kprobe_lookup_name(const char *name, unsigned int offset) > > +{ > > + kprobe_opcode_t *addr; > > + > > + addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); > > +#ifdef CONFIG_KPROBES_ON_FTRACE > > + if (addr && !offset) { > > + unsigned long faddr; > > + > > + faddr = ftrace_location_range((unsigned long)addr, > > + (unsigned long)addr + 8); > > this '8' must be (AARCH64_INSN_SIZE * 2). And here you may need to add > a comment why search the 2 instructions. (it is because arm64 uses > -fpatchable-function-entry=2.) > Got it , will fix it. > > + if (faddr) > > + addr = (kprobe_opcode_t *)faddr; > > + } This change the p->addr to ftrace_addr.
> > +#endif > > + return addr; > > +} > > + > > +bool __kprobes arch_kprobe_on_func_entry(unsigned long offset) > > +{ > > +#ifdef CONFIG_KPROBES_ON_FTRACE > > + return offset <= 8; > > Ditto. Got it, will add comment.
Thanks
Jianhua > > > +#else > > + return !offset; > > +#endif > > +} > > + > > int __init arch_init_kprobes(void) > > { > > register_kernel_break_hook(&kprobes_break_hook); > > -- > > 2.25.1 > > > > Thank you, > > > -- > Masami Hiramatsu <mhiramat@kernel.org>
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