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Subject: Re: [RFC PATCH] arm64: kprobes: Enable OPTPROBE for arm64
To:     Linuxarm <linuxarm@huawei.com>, <catalin.marinas@arm.com>,
        <will@kernel.org>, <linux-arm-kernel@lists.infradead.org>,
        <robin.murphy@arm.com>
CC:     <song.bao.hua@hisilicon.com>, <prime.zeng@hisilicon.com>,
        <linux-kernel@vger.kernel.org>
References: <1622803839-27354-1-git-send-email-liuqi115@huawei.com>
From:   "liuqi (BA)" <liuqi115@huawei.com>
Message-ID: <2409bcc3-fc5c-1e41-d7be-c81e59042c4d@huawei.com>
Date:   Wed, 23 Jun 2021 10:27:59 +0800
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Hi all,

Gentle ping..
any comments for this ?

On 2021/6/4 18:50, Qi Liu 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.
> 
> 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.
> 
> 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@huawei.com>
> ---
> TODO:
> - Veneer will be used latter to extend the range of branch and
> support long jump.
> 
>   arch/arm64/Kconfig                             |   1 +
>   arch/arm64/include/asm/kprobes.h               |  23 +++
>   arch/arm64/kernel/probes/Makefile              |   2 +
>   arch/arm64/kernel/probes/kprobes.c             |  19 ++-
>   arch/arm64/kernel/probes/opt-arm64.c           | 218 +++++++++++++++++++++++++
>   arch/arm64/kernel/probes/optprobe_trampoline.S |  81 +++++++++
>   6 files changed, 341 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 2e242dbb..ab1a795 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -189,6 +189,7 @@ config ARM64
>   	select HAVE_STACKPROTECTOR
>   	select HAVE_SYSCALL_TRACEPOINTS
>   	select HAVE_KPROBES
> +	select HAVE_OPTPROBES if !RANDOMIZE_MODULE_REGION_FULL
>   	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 5d38ff4..9e1c492 100644
> --- a/arch/arm64/include/asm/kprobes.h
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -39,6 +39,29 @@ 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[];
> +
> +#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 8e4be92..52cf5d4 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 66aac28..baaceed 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -11,6 +11,7 @@
>   #include <linux/kernel.h>
>   #include <linux/kprobes.h>
>   #include <linux/extable.h>
> +#include <linux/moduleloader.h>
>   #include <linux/slab.h>
>   #include <linux/stop_machine.h>
>   #include <linux/sched/debug.h>
> @@ -111,9 +112,21 @@ 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 0000000..09ffa75
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/opt-arm64.c
> @@ -0,0 +1,218 @@
> +// 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/kprobes.h>
> +/* for aarch64_insn_gen_branch_imm */
> +#include <asm/insn.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)
> +
> +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);
> +		free_optinsn_slot(code, 0);
> +		return -ERANGE;
> +	}
> +
> +	/* Setup template */
> +	size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
> +	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;
> +		}
> +	}
> +
> +	/* 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);
> +	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);
> +
> +	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);
> +
> +		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 0000000..95d1529
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
> @@ -0,0 +1,81 @@
> +/* 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
> +
>