[PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64
Masami Hiramatsu
mhiramat at kernel.org
Wed Aug 18 09:27:57 PDT 2021
On Wed, 18 Aug 2021 15:33:36 +0800
Qi Liu <liuqi115 at huawei.com> wrote:
> This patch introduce optprobe for ARM64. In optprobe, probed
> instruction is replaced by a branch instruction to detour
> buffer. Detour buffer contains trampoline code and a call to
> optimized_callback(). optimized_callback() calls opt_pre_handler()
> to execute kprobe handler.
>
> Performance of optprobe on Hip08 platform is test using kprobe
> example module[1] to analyze the latency of a kernel function,
> and here is the result:
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kprobes/kretprobe_example.c
>
> kprobe before optimized:
> [280709.846380] do_empty returned 0 and took 1530 ns to execute
> [280709.852057] do_empty returned 0 and took 550 ns to execute
> [280709.857631] do_empty returned 0 and took 440 ns to execute
> [280709.863215] do_empty returned 0 and took 380 ns to execute
> [280709.868787] do_empty returned 0 and took 360 ns to execute
> [280709.874362] do_empty returned 0 and took 340 ns to execute
> [280709.879936] do_empty returned 0 and took 320 ns to execute
> [280709.885505] do_empty returned 0 and took 300 ns to execute
> [280709.891075] do_empty returned 0 and took 280 ns to execute
> [280709.896646] do_empty returned 0 and took 290 ns to execute
> [280709.902220] do_empty returned 0 and took 290 ns to execute
> [280709.907807] do_empty returned 0 and took 290 ns to execute
>
> optprobe:
> [ 2965.964572] do_empty returned 0 and took 90 ns to execute
> [ 2965.969952] do_empty returned 0 and took 80 ns to execute
> [ 2965.975332] do_empty returned 0 and took 70 ns to execute
> [ 2965.980714] do_empty returned 0 and took 60 ns to execute
> [ 2965.986128] do_empty returned 0 and took 80 ns to execute
> [ 2965.991507] do_empty returned 0 and took 70 ns to execute
> [ 2965.996884] do_empty returned 0 and took 70 ns to execute
> [ 2966.002262] do_empty returned 0 and took 80 ns to execute
> [ 2966.007642] do_empty returned 0 and took 70 ns to execute
> [ 2966.013020] do_empty returned 0 and took 70 ns to execute
> [ 2966.018400] do_empty returned 0 and took 70 ns to execute
> [ 2966.023779] do_empty returned 0 and took 70 ns to execute
> [ 2966.029158] do_empty returned 0 and took 70 ns to execute
>
> Signed-off-by: Qi Liu <liuqi115 at huawei.com>
Thanks for updating. This looks good to me. :D
Acked-by: Masami Hiramatsu <mhiramat at kernel.org>
Thank you!
>
> Note:
> To guarantee the offset between probe point and kprobe pre_handler
> is smaller than 128MiB, users should set
> CONFIG_RANDOMIZE_MODULE_REGION_FULL=N or set nokaslr in command line, or
> optprobe will not work and fall back to normal kprobe.
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/kprobes.h | 24 ++
> arch/arm64/kernel/probes/Makefile | 2 +
> arch/arm64/kernel/probes/kprobes.c | 19 +-
> arch/arm64/kernel/probes/opt_arm64.c | 276 ++++++++++++++++++
> .../arm64/kernel/probes/optprobe_trampoline.S | 37 +++
> 6 files changed, 356 insertions(+), 3 deletions(-)
> create mode 100644 arch/arm64/kernel/probes/opt_arm64.c
> create mode 100644 arch/arm64/kernel/probes/optprobe_trampoline.S
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b5b13a932561..b05d1d275d87 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -200,6 +200,7 @@ config ARM64
> select HAVE_STACKPROTECTOR
> select HAVE_SYSCALL_TRACEPOINTS
> select HAVE_KPROBES
> + select HAVE_OPTPROBES
> select HAVE_KRETPROBES
> select HAVE_GENERIC_VDSO
> select IOMMU_DMA if IOMMU_SUPPORT
> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> index 5d38ff4a4806..6b2fdd2ad7d8 100644
> --- a/arch/arm64/include/asm/kprobes.h
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -39,6 +39,30 @@ void arch_remove_kprobe(struct kprobe *);
> int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
> int kprobe_exceptions_notify(struct notifier_block *self,
> unsigned long val, void *data);
> +
> +#define RELATIVEJUMP_SIZE (4)
> +#define MAX_COPIED_INSN DIV_ROUND_UP(RELATIVEJUMP_SIZE, sizeof(kprobe_opcode_t))
> +struct arch_optimized_insn {
> + kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
> + /* detour code buffer */
> + kprobe_opcode_t *insn;
> +};
> +
> +/* optinsn template addresses */
> +extern __visible kprobe_opcode_t optprobe_template_entry[];
> +extern __visible kprobe_opcode_t optprobe_template_val[];
> +extern __visible kprobe_opcode_t optprobe_template_call[];
> +extern __visible kprobe_opcode_t optprobe_template_end[];
> +extern __visible kprobe_opcode_t optprobe_template_restore_begin[];
> +extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn[];
> +extern __visible kprobe_opcode_t optprobe_template_restore_end[];
> +extern __visible kprobe_opcode_t optprobe_template_max_length[];
> +
> +#define MAX_OPTIMIZED_LENGTH 4
> +#define MAX_OPTINSN_SIZE \
> + ((unsigned long)optprobe_template_end - \
> + (unsigned long)optprobe_template_entry)
> +
> void kretprobe_trampoline(void);
> void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
>
> diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
> index 8e4be92e25b1..07105fd3261d 100644
> --- a/arch/arm64/kernel/probes/Makefile
> +++ b/arch/arm64/kernel/probes/Makefile
> @@ -4,3 +4,5 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \
> simulate-insn.o
> obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \
> simulate-insn.o
> +obj-$(CONFIG_OPTPROBES) += opt_arm64.o \
> + optprobe_trampoline.o
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 6dbcc89f6662..83755ad62abe 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -11,6 +11,7 @@
> #include <linux/kasan.h>
> #include <linux/kernel.h>
> #include <linux/kprobes.h>
> +#include <linux/moduleloader.h>
> #include <linux/sched/debug.h>
> #include <linux/set_memory.h>
> #include <linux/slab.h>
> @@ -113,9 +114,21 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>
> void *alloc_insn_page(void)
> {
> - return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
> - GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
> - NUMA_NO_NODE, __builtin_return_address(0));
> + void *page;
> +
> + page = module_alloc(PAGE_SIZE);
> + if (!page)
> + return NULL;
> +
> + set_vm_flush_reset_perms(page);
> + /*
> + * First make the page read-only, and only then make it executable to
> + * prevent it from being W+X in between.
> + */
> + set_memory_ro((unsigned long)page, 1);
> + set_memory_x((unsigned long)page, 1);
> +
> + return page;
> }
>
> /* arm kprobe: install breakpoint in text */
> diff --git a/arch/arm64/kernel/probes/opt_arm64.c b/arch/arm64/kernel/probes/opt_arm64.c
> new file mode 100644
> index 000000000000..4de535bee534
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/opt_arm64.c
> @@ -0,0 +1,276 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Code for Kernel probes Jump optimization.
> + *
> + * Copyright (C) 2021 Hisilicon Limited
> + */
> +
> +#include <linux/jump_label.h>
> +#include <linux/kprobes.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/insn.h>
> +#include <asm/kprobes.h>
> +#include <asm/patching.h>
> +
> +#define TMPL_VAL_IDX \
> + (optprobe_template_val - optprobe_template_entry)
> +#define TMPL_CALL_BACK \
> + (optprobe_template_call - optprobe_template_entry)
> +#define TMPL_END_IDX \
> + (optprobe_template_end - optprobe_template_entry)
> +#define TMPL_RESTORE_ORIGN_INSN \
> + (optprobe_template_restore_orig_insn - optprobe_template_entry)
> +#define TMPL_RESTORE_END \
> + (optprobe_template_restore_end - optprobe_template_entry)
> +#define TMPL_MAX_LENGTH \
> + (optprobe_template_max_length - optprobe_template_entry)
> +#define OPTPROBE_BATCH_SIZE 64
> +
> +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
> +{
> + return 0;
> +}
> +
> +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
> +{
> + return optinsn->insn != NULL;
> +}
> +
> +int arch_within_optimized_kprobe(struct optimized_kprobe *op,
> + unsigned long addr)
> +{
> + return ((unsigned long)op->kp.addr <= addr &&
> + (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
> +}
> +
> +static void
> +optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
> +{
> + /* This is possible if op is under delayed unoptimizing */
> + if (kprobe_disabled(&op->kp))
> + return;
> +
> + preempt_disable();
> +
> + if (kprobe_running()) {
> + kprobes_inc_nmissed_count(&op->kp);
> + } else {
> + __this_cpu_write(current_kprobe, &op->kp);
> + regs->pc = (unsigned long)op->kp.addr;
> + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> + opt_pre_handler(&op->kp, regs);
> + __this_cpu_write(current_kprobe, NULL);
> + }
> +
> + preempt_enable_no_resched();
> +}
> +NOKPROBE_SYMBOL(optimized_callback)
> +
> +static bool is_offset_in_range(unsigned long start, unsigned long end)
> +{
> + long offset = end - start;
> +
> + /*
> + * Verify if the address gap is in 128MiB range, because this uses
> + * a relative jump.
> + *
> + * kprobe opt use a 'b' instruction to branch to optinsn.insn.
> + * According to ARM manual, branch instruction is:
> + *
> + * 31 30 25 0
> + * +----+---+---+---+---+---+---------------+
> + * |cond| 0 | 0 | 1 | 0 | 1 | imm26 |
> + * +----+---+---+---+---+---+---------------+
> + *
> + * imm26 is a signed 26 bits integer. The real branch offset is computed
> + * by: imm64 = SignExtend(imm26:'00', 64);
> + *
> + * So the maximum forward branch should be:
> + * (0x01ffffff << 2) = 0x07fffffc
> + * The maximum backward branch should be:
> + * (0xfe000000 << 2) = 0xFFFFFFFFF8000000 = -0x08000000
> + *
> + * We can simply check (rel & 0xf8000003):
> + * if rel is positive, (rel & 0xf8000003) should be 0
> + * if rel is negitive, (rel & 0xf8000003) should be 0xf8000000
> + * the last '3' is used for alignment checking.
> + */
> + return (offset >= -0x8000000 && offset <= 0x7fffffc && !(offset & 0x3));
> +}
> +
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
> + struct kprobe *orig)
> +{
> + kprobe_opcode_t *code, *buf;
> + void **addrs;
> + u32 insn;
> + int ret, i;
> +
> + addrs = kcalloc(TMPL_MAX_LENGTH, sizeof(void *), GFP_KERNEL);
> + if (!addrs)
> + return -ENOMEM;
> +
> + buf = kcalloc(TMPL_MAX_LENGTH, sizeof(kprobe_opcode_t), GFP_KERNEL);
> + if (!buf) {
> + kfree(addrs);
> + return -ENOMEM;
> + }
> +
> + code = get_optinsn_slot();
> + if (!code) {
> + kfree(addrs);
> + kfree(buf);
> + return -ENOMEM;
> + }
> +
> + if (!is_offset_in_range((unsigned long)code,
> + (unsigned long)orig->addr + 8)) {
> + ret = -ERANGE;
> + goto error;
> + }
> +
> + if (!is_offset_in_range((unsigned long)code + TMPL_CALL_BACK,
> + (unsigned long)optimized_callback)) {
> + ret = -ERANGE;
> + goto error;
> + }
> +
> + if (!is_offset_in_range((unsigned long)&code[TMPL_RESTORE_END],
> + (unsigned long)op->kp.addr + 4)) {
> + ret = -ERANGE;
> + goto error;
> + }
> +
> + memcpy(buf, optprobe_template_entry,
> + TMPL_END_IDX * sizeof(kprobe_opcode_t));
> +
> + buf[TMPL_VAL_IDX] = FIELD_GET(GENMASK(31, 0), (unsigned long long)op);
> + buf[TMPL_VAL_IDX + 1] =
> + FIELD_GET(GENMASK(63, 32), (unsigned long long)op);
> + buf[TMPL_RESTORE_ORIGN_INSN] = orig->opcode;
> +
> + insn = aarch64_insn_gen_branch_imm(
> + (unsigned long)(&code[TMPL_CALL_BACK]),
> + (unsigned long)optimized_callback, AARCH64_INSN_BRANCH_LINK);
> + buf[TMPL_CALL_BACK] = insn;
> +
> + insn = aarch64_insn_gen_branch_imm(
> + (unsigned long)(&code[TMPL_RESTORE_END]),
> + (unsigned long)(op->kp.addr) + 4, AARCH64_INSN_BRANCH_NOLINK);
> + buf[TMPL_RESTORE_END] = insn;
> +
> + /* Setup template */
> + for (i = 0; i < TMPL_MAX_LENGTH; i++)
> + addrs[i] = code + i;
> +
> + ret = aarch64_insn_patch_text(addrs, buf, TMPL_MAX_LENGTH);
> + if (ret < 0)
> + goto error;
> +
> + flush_icache_range((unsigned long)code,
> + (unsigned long)(&code[TMPL_END_IDX]));
> +
> + /* Set op->optinsn.insn means prepared. */
> + op->optinsn.insn = code;
> +
> +out:
> + kfree(addrs);
> + kfree(buf);
> + return ret;
> +
> +error:
> + free_optinsn_slot(code, 0);
> + goto out;
> +}
> +
> +void arch_optimize_kprobes(struct list_head *oplist)
> +{
> + struct optimized_kprobe *op, *tmp;
> + kprobe_opcode_t *insns;
> + void **addrs;
> + int i = 0;
> +
> + addrs = kcalloc(OPTPROBE_BATCH_SIZE, sizeof(void *), GFP_KERNEL);
> + if (!addrs)
> + return;
> +
> + insns = kcalloc(OPTPROBE_BATCH_SIZE, sizeof(kprobe_opcode_t), GFP_KERNEL);
> + if (!insns) {
> + kfree(addrs);
> + return;
> + }
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + WARN_ON(kprobe_disabled(&op->kp));
> +
> + /*
> + * Backup instructions which will be replaced
> + * by jump address
> + */
> + memcpy(op->optinsn.copied_insn, op->kp.addr,
> + RELATIVEJUMP_SIZE);
> +
> + addrs[i] = (void *)op->kp.addr;
> + insns[i] = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr,
> + (unsigned long)op->optinsn.insn,
> + AARCH64_INSN_BRANCH_NOLINK);
> +
> + list_del_init(&op->list);
> + if (++i == OPTPROBE_BATCH_SIZE)
> + break;
> + }
> +
> + aarch64_insn_patch_text(addrs, insns, i);
> + kfree(addrs);
> + kfree(insns);
> +}
> +
> +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> +{
> + arch_arm_kprobe(&op->kp);
> +}
> +
> +/*
> + * Recover original instructions and breakpoints from relative jumps.
> + * Caller must call with locking kprobe_mutex.
> + */
> +void arch_unoptimize_kprobes(struct list_head *oplist,
> + struct list_head *done_list)
> +{
> + struct optimized_kprobe *op, *tmp;
> + kprobe_opcode_t *insns;
> + void **addrs;
> + int i = 0;
> +
> + addrs = kcalloc(OPTPROBE_BATCH_SIZE, sizeof(void *), GFP_KERNEL);
> + if (!addrs)
> + return;
> +
> + insns = kcalloc(OPTPROBE_BATCH_SIZE, sizeof(kprobe_opcode_t), GFP_KERNEL);
> + if (!insns) {
> + kfree(addrs);
> + return;
> + }
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + addrs[i] = (void *)op->kp.addr;
> + insns[i] = BRK64_OPCODE_KPROBES;
> + list_move(&op->list, done_list);
> +
> + if (++i == OPTPROBE_BATCH_SIZE)
> + break;
> + }
> +
> + aarch64_insn_patch_text(addrs, insns, i);
> + kfree(addrs);
> + kfree(insns);
> +}
> +
> +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
> +{
> + if (op->optinsn.insn) {
> + free_optinsn_slot(op->optinsn.insn, 1);
> + op->optinsn.insn = NULL;
> + }
> +}
> diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S
> new file mode 100644
> index 000000000000..24d713d400cd
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * trampoline entry and return code for optprobes.
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm-offsets.h>
> +#include <asm/assembler.h>
> +
> + .global optprobe_template_entry
> +optprobe_template_entry:
> + sub sp, sp, #PT_REGS_SIZE
> + save_all_base_regs
> + /* Get parameters to optimized_callback() */
> + ldr x0, 1f
> + mov x1, sp
> + /* Branch to optimized_callback() */
> + .global optprobe_template_call
> +optprobe_template_call:
> + nop
> + restore_all_base_regs
> + ldr lr, [sp, #S_LR]
> + add sp, sp, #PT_REGS_SIZE
> + .global optprobe_template_restore_orig_insn
> +optprobe_template_restore_orig_insn:
> + nop
> + .global optprobe_template_restore_end
> +optprobe_template_restore_end:
> + nop
> + .global optprobe_template_end
> +optprobe_template_end:
> + .global optprobe_template_val
> +optprobe_template_val:
> + 1: .long 0
> + .long 0
> + .global optprobe_template_max_length
> +optprobe_template_max_length:
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat at kernel.org>
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