[PATCH] arm64: kprobe: Enable OPTPROBE for arm64
Masami Hiramatsu
mhiramat at kernel.org
Wed Jul 21 01:41:53 PDT 2021
Hi Qi,
Thanks for your effort!
On Mon, 19 Jul 2021 20:24:17 +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.
OK so this will replace only one instruction.
>
> Limitations:
> - We only support !CONFIG_RANDOMIZE_MODULE_REGION_FULL case to
> guarantee the offset between probe point and kprobe pre_handler
> is not larger than 128MiB.
Hmm, shouldn't we depends on !CONFIG_ARM64_MODULE_PLTS? Or,
allocate an intermediate trampoline area similar to arm optprobe
does.
>
> 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
Great result!
I have other comments on the code below.
[...]
> 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;
Isn't this a separated change? Or any reason why you have to
change this function?
> }
>
> /* 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..ff72f6275e71
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/opt-arm64.c
> @@ -0,0 +1,217 @@
> +// 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)
> +
> +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_branch_range(long offset)
> +{
> + return (offset >= -0x08000000 && offset <= 0x07fffffc && !(offset & 0x3));
> +}
> +
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
> +{
> + kprobe_opcode_t *code;
> + long rel_chk;
> + u32 insn, size;
> + int ret, i;
> + void *addr;
> +
> + code = get_optinsn_slot();
> + if (!code)
> + return -ENOMEM;
> +
> + /*
> + * 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) = 1720x07fffffc = 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.
> + */
> + rel_chk = (unsigned long)code -
> + (unsigned long)orig->addr + 8;
> + if (!is_offset_in_branch_range(rel_chk)) {
> + pr_err("%s is out of branch range.\n", orig->symbol_name);
Because the optprobe is an optional optimization (it can fail back to
normal kprobe), you don't need to show this message as an error.
pr_debug() or pr_info() will be enough.
> + free_optinsn_slot(code, 0);
> + return -ERANGE;
> + }
> +
> + /* Setup template */
> + size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
Why would you use 'int' instead of 'kprobe_opcode_t' here?
> + for (i = 0; i < size; i++) {
> + addr = code + i;
> + insn = *(optprobe_template_entry + i);
> + ret = aarch64_insn_patch_text(&addr, &insn, 1);
> + if (ret < 0) {
> + free_optinsn_slot(code, 0);
> + return -ERANGE;
> + }
> + }
This is too much calling stop_machine() in the loop.
Please try to allocate an array of addresses and call
aarch64_insn_patch_text() once.
Or, as same as x86, allocate a temporary trampoline buffer and modify code
as you like, and patch it once (with following aarch64_insn_patch_text()
calls.)
> +
> + /* Set probe information */
> + addr = code + TMPL_VAL_IDX;
> + insn = (unsigned long long)op & 0xffffffff;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + addr = addr + 4;
> + insn = ((unsigned long long)op & GENMASK_ULL(63, 32)) >> 32;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + addr = code + TMPL_CALL_BACK;
> + insn = aarch64_insn_gen_branch_imm((unsigned long)addr,
> + (unsigned long)optimized_callback,
> + AARCH64_INSN_BRANCH_LINK);
If you use the branch here (and later), you may also need to
do the branch_range check here too.
(trampoline -> optimized_callback())
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + /* The original probed instruction */
> + addr = code + TMPL_RESTORE_ORIGN_INSN;
> + insn = orig->opcode;
> + aarch64_insn_patch_text(&addr, &insn, 1);
> +
> + /* Jump back to next instruction */
> + addr = code + TMPL_RESTORE_END;
> + insn = aarch64_insn_gen_branch_imm(
> + (unsigned long)(&code[TMPL_RESTORE_END]),
> + (unsigned long)(op->kp.addr) + 4,
> + AARCH64_INSN_BRANCH_NOLINK);
> + aarch64_insn_patch_text(&addr, &insn, 1);
Ditto.
> +
> + flush_icache_range((unsigned long)code,
> + (unsigned long)(&code[TMPL_END_IDX]));
> + /* Set op->optinsn.insn means prepared. */
> + op->optinsn.insn = code;
> + return 0;
> +}
> +
> +void arch_optimize_kprobes(struct list_head *oplist)
> +{
> + struct optimized_kprobe *op, *tmp;
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + u32 insn;
> +
> + 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);
> + insn = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr,
> + (unsigned long)op->optinsn.insn,
> + AARCH64_INSN_BRANCH_NOLINK);
> +
> + WARN_ON(insn == 0);
> +
> + aarch64_insn_patch_text((void *)&(op->kp.addr), &insn, 1);
Hmm, there is room for improvement.
Since aarch64_insn_patch_text() is a batch patching API, this should
optimize probes in batch instead of calling it on each probe.
Thank you,
> +
> + list_del_init(&op->list);
> + }
> +}
> +
> +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;
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + arch_unoptimize_kprobe(op);
> + list_move(&op->list, done_list);
> + }
> +}
> +
> +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..13729cb279b8
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
> @@ -0,0 +1,80 @@
> +/* 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
> + stp x0, x1, [sp, #S_X0]
> + stp x2, x3, [sp, #S_X2]
> + stp x4, x5, [sp, #S_X4]
> + stp x6, x7, [sp, #S_X6]
> + stp x8, x9, [sp, #S_X8]
> + stp x10, x11, [sp, #S_X10]
> + stp x12, x13, [sp, #S_X12]
> + stp x14, x15, [sp, #S_X14]
> + stp x16, x17, [sp, #S_X16]
> + stp x18, x19, [sp, #S_X18]
> + stp x20, x21, [sp, #S_X20]
> + stp x22, x23, [sp, #S_X22]
> + stp x24, x25, [sp, #S_X24]
> + stp x26, x27, [sp, #S_X26]
> + stp x28, x29, [sp, #S_X28]
> + add x0, sp, #PT_REGS_SIZE
> + stp lr, x0, [sp, #S_LR]
> + /*
> + * Construct a useful saved PSTATE
> + */
> + mrs x0, nzcv
> + mrs x1, daif
> + orr x0, x0, x1
> + mrs x1, CurrentEL
> + orr x0, x0, x1
> + mrs x1, SPSel
> + orr x0, x0, x1
> + stp xzr, x0, [sp, #S_PC]
> + /* Get parameters to optimized_callback() */
> + ldr x0, 1f
> + mov x1, sp
> + /* Branch to optimized_callback() */
> + .global optprobe_template_call
> +optprobe_template_call:
> + nop
> + /* Restore registers */
> + ldr x0, [sp, #S_PSTATE]
> + and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
> + msr nzcv, x0
> + ldp x0, x1, [sp, #S_X0]
> + ldp x2, x3, [sp, #S_X2]
> + ldp x4, x5, [sp, #S_X4]
> + ldp x6, x7, [sp, #S_X6]
> + ldp x8, x9, [sp, #S_X8]
> + ldp x10, x11, [sp, #S_X10]
> + ldp x12, x13, [sp, #S_X12]
> + ldp x14, x15, [sp, #S_X14]
> + ldp x16, x17, [sp, #S_X16]
> + ldp x18, x19, [sp, #S_X18]
> + ldp x20, x21, [sp, #S_X20]
> + ldp x22, x23, [sp, #S_X22]
> + ldp x24, x25, [sp, #S_X24]
> + ldp x26, x27, [sp, #S_X26]
> + ldp x28, x29, [sp, #S_X28]
> + 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
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat at kernel.org>
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