Messages in this thread | | | Date | Fri, 17 Dec 2021 16:40:19 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v2 2/2] arm64: kprobes: add support for KPROBES_ON_FTRACE |
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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.
> + 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);
> + > + __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.
> + 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.)
> + if (faddr) > + addr = (kprobe_opcode_t *)faddr; > + } > +#endif > + return addr; > +} > + > +bool __kprobes arch_kprobe_on_func_entry(unsigned long offset) > +{ > +#ifdef CONFIG_KPROBES_ON_FTRACE > + return offset <= 8;
Ditto.
> +#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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