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+0x4 [DISABLED][FTRACE] Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> --- 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. Applied after arm64 FTRACE_WITH_REGS: http://lists.infradead.org/pipermail/linux-arm-kernel/2019-August/674404.html Changes since v4: - correct reg->pc: probed on foo, then pre_handler see foo+0x4, while post_handler see foo+0x8 Changes since v3: - move kprobe_lookup_name() and arch_kprobe_on_func_entry to ftrace.c since we only want to choose the ftrace entry for KPROBES_ON_FTRACE. - only choose ftrace entry if (addr && !offset) Changes since v2: - remove patch1, make it a single cleanup patch - remove "This patch" in the change log - implement arm64's kprobe_lookup_name() and arch_kprobe_on_func_entry instead of patching the common kprobes code Changes since v1: - make the kprobes/x86: use instruction_pointer and instruction_pointer_set as patch1 - add Masami's ACK to patch1 - add some description about KPROBES_ON_FTRACE and why we need it on arm64 - correct the log before the patch - remove the consolidation patch, make it as TODO - only adjust kprobe's addr when KPROBE_FLAG_FTRACE is set - if KPROBES_ON_FTRACE, ftrace_call_adjust() the kprobe's addr before calling ftrace_location() - update the kprobes-on-ftrace/arch-support.txt in doc .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- arch/arm64/Kconfig | 1 + arch/arm64/kernel/probes/Makefile | 1 + arch/arm64/kernel/probes/ftrace.c | 83 +++++++++++++++++++ 4 files changed, 86 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 68f266944d5f..e8358a38981c 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 663392d1eae2..928700f15e23 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -167,6 +167,7 @@ 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/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..9f80905f02fa --- /dev/null +++ b/arch/arm64/kernel/probes/ftrace.c @@ -0,0 +1,83 @@ +// 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> + +/* 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) +{ + struct kprobe *p; + struct kprobe_ctlblk *kcb; + + /* Preempt is disabled by ftrace */ + p = get_kprobe((kprobe_opcode_t *)ip); + if (unlikely(!p) || kprobe_disabled(p)) + return; + + 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); + __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); + +kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) +{ + unsigned long addr = kallsyms_lookup_name(name); + + if (addr && !offset) { + unsigned long faddr; + /* + * with -fpatchable-function-entry=2, the first 4 bytes is the + * LR saver, then the actual call insn. So ftrace location is + * always on the first 4 bytes offset. + */ + faddr = ftrace_location_range(addr, + addr + AARCH64_INSN_SIZE); + if (faddr) + return (kprobe_opcode_t *)faddr; + } + return (kprobe_opcode_t *)addr; +} + +bool arch_kprobe_on_func_entry(unsigned long offset) +{ + return offset <= AARCH64_INSN_SIZE; +} + +int arch_prepare_kprobe_ftrace(struct kprobe *p) +{ + p->ainsn.api.insn = NULL; + return 0; +} -- 2.23.0.rc1
