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    Subject[PATCH] arm64/kprobes: Add support for KPROBES_ON_FTRACE
    Date
    This is the arm64 version of ftrace-based kprobes to avoid the overhead
    with regular kprobes, by using the ftrace infrastructure.

    Signed-off-by: Jianlin Lv <iecedge@gmail.com>
    ---
    .../debug/kprobes-on-ftrace/arch-support.txt | 2 +-
    arch/arm64/Kconfig | 1 +
    arch/arm64/kernel/probes/Makefile | 1 +
    arch/arm64/kernel/probes/kprobes-ftrace.c | 81 +++++++++++++++++++
    include/linux/kprobes.h | 2 +
    kernel/kprobes.c | 4 +-
    6 files changed, 88 insertions(+), 3 deletions(-)
    create mode 100644 arch/arm64/kernel/probes/kprobes-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 b3697f4c806e..fadbd4513c91 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 |
    | csky: | ok |
    | hexagon: | TODO |
    | ia64: | TODO |
    diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    index 1652a9800ebe..7271d97e035a 100644
    --- a/arch/arm64/Kconfig
    +++ b/arch/arm64/Kconfig
    @@ -204,6 +204,7 @@ 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..dab2fa4dba81 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) += kprobes-ftrace.o
    diff --git a/arch/arm64/kernel/probes/kprobes-ftrace.c b/arch/arm64/kernel/probes/kprobes-ftrace.c
    new file mode 100644
    index 000000000000..fcfa6b6533a0
    --- /dev/null
    +++ b/arch/arm64/kernel/probes/kprobes-ftrace.c
    @@ -0,0 +1,81 @@
    +// SPDX-License-Identifier: GPL-2.0-or-later
    +/*
    + * Dynamic Ftrace based Kprobes Optimization
    + *
    + * Copyright (C) Hitachi Ltd., 2012
    + */
    +#include <linux/kprobes.h>
    +
    +int arch_check_ftrace_location(struct kprobe *p)
    +{
    + unsigned long addr = (unsigned long)p->addr;
    +
    + /* ftrace location at the BL in the callsite (<function-entry> + AARCH64_INSN_SIZE) */
    + if (ftrace_location(addr) == (addr + AARCH64_INSN_SIZE)) {
    +#ifdef CONFIG_KPROBES_ON_FTRACE
    + p->flags |= KPROBE_FLAG_FTRACE;
    +#else /* !CONFIG_KPROBES_ON_FTRACE */
    + return -EINVAL;
    +#endif
    + }
    + return 0;
    +}
    +
    +/* 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 pt_regs *regs;
    + struct kprobe *p;
    + struct kprobe_ctlblk *kcb;
    + int bit;
    +
    + bit = ftrace_test_recursion_trylock(ip, parent_ip);
    + if (bit < 0)
    + return;
    +
    + regs = ftrace_get_regs(fregs);
    + p = get_kprobe((kprobe_opcode_t *) (ip - AARCH64_INSN_SIZE));
    + if (unlikely(!p) || kprobe_disabled(p))
    + goto out;
    +
    + 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 - 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 4byte nop
    + */
    + instruction_pointer_set(regs, ip);
    + 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);
    + }
    +out:
    + ftrace_test_recursion_unlock(bit);
    +}
    +NOKPROBE_SYMBOL(kprobe_ftrace_handler);
    +
    +int arch_prepare_kprobe_ftrace(struct kprobe *p)
    +{
    + p->ainsn.api.insn = NULL;
    + return 0;
    +}
    +
    diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
    index 55041d2f884d..83a479908029 100644
    --- a/include/linux/kprobes.h
    +++ b/include/linux/kprobes.h
    @@ -392,6 +392,8 @@ static inline int arch_prepare_kprobe_ftrace(struct kprobe *p)
    }
    #endif /* CONFIG_KPROBES_ON_FTRACE */

    +int arch_check_ftrace_location(struct kprobe *p);
    +
    /* Get the kprobe at this addr (if any) - called with preemption disabled */
    struct kprobe *get_kprobe(void *addr);

    diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    index f214f8c088ed..34754c2fe14e 100644
    --- a/kernel/kprobes.c
    +++ b/kernel/kprobes.c
    @@ -1534,7 +1534,7 @@ static inline int warn_kprobe_rereg(struct kprobe *p)
    return ret;
    }

    -static int check_ftrace_location(struct kprobe *p)
    +int __weak arch_check_ftrace_location(struct kprobe *p)
    {
    unsigned long addr = (unsigned long)p->addr;

    @@ -1553,7 +1553,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
    {
    int ret;

    - ret = check_ftrace_location(p);
    + ret = arch_check_ftrace_location(p);
    if (ret)
    return ret;
    jump_label_lock();
    --
    2.25.1
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