Re: [PATCH v2 2/5] LoongArch: Add kprobe support
From: Huacai Chen
Date: Sun Nov 13 2022 - 23:42:10 EST
Hi, Tiezhu,
On Wed, Sep 28, 2022 at 8:50 AM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> Kprobes allows you to trap at almost any kernel address and
> execute a callback function, this commit adds kprobe support
> for LoongArch.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
> arch/loongarch/Kconfig | 1 +
> arch/loongarch/include/asm/inst.h | 12 ++
> arch/loongarch/include/asm/kprobes.h | 44 +++++
> arch/loongarch/kernel/Makefile | 2 +
> arch/loongarch/kernel/kprobes.c | 312 +++++++++++++++++++++++++++++++++++
> arch/loongarch/mm/fault.c | 3 +
> 6 files changed, 374 insertions(+)
> create mode 100644 arch/loongarch/include/asm/kprobes.h
> create mode 100644 arch/loongarch/kernel/kprobes.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index be8389f..8debd70 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -94,6 +94,7 @@ config LOONGARCH
> select HAVE_IOREMAP_PROT
> select HAVE_IRQ_EXIT_ON_IRQ_STACK
> select HAVE_IRQ_TIME_ACCOUNTING
> + select HAVE_KPROBES
> select HAVE_MOD_ARCH_SPECIFIC
> select HAVE_NMI
> select HAVE_PCI
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 93d5cd4..fc8879b 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -21,6 +21,10 @@
>
> #define ADDR_IMM(addr, INSN) ((addr & ADDR_IMMMASK_##INSN) >> ADDR_IMMSHIFT_##INSN)
>
> +enum reg0i15_op {
> + break_op = 0x54,
> +};
> +
> enum reg0i26_op {
> b_op = 0x14,
> bl_op = 0x15,
> @@ -38,6 +42,8 @@ enum reg1i20_op {
> enum reg1i21_op {
> beqz_op = 0x10,
> bnez_op = 0x11,
> + bceqz_op = 0x48000000,
> + bcnez_op = 0x48000100,
> };
>
> enum reg2_op {
> @@ -167,6 +173,11 @@ enum reg3sa2_op {
> alsld_op = 0x16,
> };
>
> +struct reg0i15_format {
> + unsigned int immediate : 15;
> + unsigned int opcode : 17;
> +};
> +
> struct reg0i26_format {
> unsigned int immediate_h : 10;
> unsigned int immediate_l : 16;
> @@ -252,6 +263,7 @@ struct reg3sa2_format {
>
> union loongarch_instruction {
> unsigned int word;
> + struct reg0i15_format reg0i15_format;
> struct reg0i26_format reg0i26_format;
> struct reg1i20_format reg1i20_format;
> struct reg1i21_format reg1i21_format;
> diff --git a/arch/loongarch/include/asm/kprobes.h b/arch/loongarch/include/asm/kprobes.h
> new file mode 100644
> index 0000000..afcf254
> --- /dev/null
> +++ b/arch/loongarch/include/asm/kprobes.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_LOONGARCH_KPROBES_H
> +#define __ASM_LOONGARCH_KPROBES_H
> +
> +#include <asm-generic/kprobes.h>
> +
> +#ifdef CONFIG_KPROBES
> +
> +#include <asm/inst.h>
> +
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +#define MAX_INSN_SIZE 2
> +
> +#define flush_insn_slot(p) do { } while (0)
We don't need an ibar here?
> +#define kretprobe_blacklist_size 0
> +
> +typedef union loongarch_instruction kprobe_opcode_t;
> +
> +/* Architecture specific copy of original instruction */
> +struct arch_specific_insn {
> + /* copy of the original instruction */
> + kprobe_opcode_t *insn;
> +};
> +
> +struct prev_kprobe {
> + struct kprobe *kp;
> + unsigned long status;
> + unsigned long saved_irq;
> + unsigned long saved_era;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> + unsigned long kprobe_status;
> + unsigned long kprobe_saved_irq;
> + unsigned long kprobe_saved_era;
> + struct prev_kprobe prev_kprobe;
> +};
> +
> +void arch_remove_kprobe(struct kprobe *p);
> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr);
> +
> +#endif /* CONFIG_KPROBES */
> +#endif /* __ASM_LOONGARCH_KPROBES_H */
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 5358144..ff98d8a 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -33,4 +33,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>
> obj-$(CONFIG_PERF_EVENTS) += perf_event.o perf_regs.o
>
> +obj-$(CONFIG_KPROBES) += kprobes.o
> +
> CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
> new file mode 100644
> index 0000000..c11f6e0
> --- /dev/null
> +++ b/arch/loongarch/kernel/kprobes.c
> @@ -0,0 +1,312 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/kprobes.h>
> +#include <linux/kdebug.h>
> +#include <asm/break.h>
> +
> +static const union loongarch_instruction breakpoint_insn = {
> + .reg0i15_format = {
> + .opcode = break_op,
> + .immediate = BRK_KPROBE_BP,
> + }
> +};
> +
> +static const union loongarch_instruction singlestep_insn = {
> + .reg0i15_format = {
> + .opcode = break_op,
> + .immediate = BRK_KPROBE_SSTEPBP,
> + }
> +};
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe);
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static bool insns_are_not_supported(union loongarch_instruction insn)
> +{
> + switch (insn.reg2i14_format.opcode) {
> + case llw_op:
> + case lld_op:
> + case scw_op:
> + case scd_op:
> + pr_notice("kprobe: ll or sc instructions are not supported\n");
> + return true;
> + }
> +
> + switch (insn.reg1i21_format.opcode) {
> + case bceqz_op:
> + case bcnez_op:
> + pr_notice("kprobe: bceqz or bcnez instructions are not supported\n");
> + return true;
> + }
> +
> + return false;
> +}
> +NOKPROBE_SYMBOL(insns_are_not_supported);
> +
> +int arch_prepare_kprobe(struct kprobe *p)
> +{
> + union loongarch_instruction insn;
> +
> + insn = p->addr[0];
> + if (insns_are_not_supported(insn))
> + return -EINVAL;
> +
> + p->ainsn.insn = get_insn_slot();
> + if (!p->ainsn.insn)
> + return -ENOMEM;
> +
> + p->ainsn.insn[0] = *p->addr;
> + p->ainsn.insn[1] = singlestep_insn;
> +
> + p->opcode = *p->addr;
> +
> + return 0;
> +}
> +NOKPROBE_SYMBOL(arch_prepare_kprobe);
> +
> +/* Install breakpoint in text */
> +void arch_arm_kprobe(struct kprobe *p)
> +{
> + *p->addr = breakpoint_insn;
> +}
> +NOKPROBE_SYMBOL(arch_arm_kprobe);
> +
> +/* Remove breakpoint from text */
> +void arch_disarm_kprobe(struct kprobe *p)
> +{
> + *p->addr = p->opcode;
> +}
> +NOKPROBE_SYMBOL(arch_disarm_kprobe);
> +
> +void arch_remove_kprobe(struct kprobe *p)
> +{
> + if (p->ainsn.insn) {
> + free_insn_slot(p->ainsn.insn, 0);
> + p->ainsn.insn = NULL;
> + }
> +}
> +NOKPROBE_SYMBOL(arch_remove_kprobe);
> +
> +static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> + kcb->prev_kprobe.kp = kprobe_running();
> + kcb->prev_kprobe.status = kcb->kprobe_status;
> + kcb->prev_kprobe.saved_irq = kcb->kprobe_saved_irq;
> + kcb->prev_kprobe.saved_era = kcb->kprobe_saved_era;
> +}
> +NOKPROBE_SYMBOL(save_previous_kprobe);
> +
> +static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> + __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> + kcb->kprobe_status = kcb->prev_kprobe.status;
> + kcb->kprobe_saved_irq = kcb->prev_kprobe.saved_irq;
> + kcb->kprobe_saved_era = kcb->prev_kprobe.saved_era;
> +}
> +NOKPROBE_SYMBOL(restore_previous_kprobe);
> +
> +static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb)
> +{
> + __this_cpu_write(current_kprobe, p);
> + kcb->kprobe_saved_irq = regs->csr_prmd & CSR_PRMD_PIE;
> + kcb->kprobe_saved_era = regs->csr_era;
> +}
> +NOKPROBE_SYMBOL(set_current_kprobe);
> +
> +static bool insns_are_not_simulated(struct kprobe *p, struct pt_regs *regs)
> +{
> + if (is_branch_ins(&p->opcode)) {
> + simu_branch(regs, p->opcode);
> + return false;
> + } else if (is_pc_ins(&p->opcode)) {
> + simu_pc(regs, p->opcode);
> + return false;
> + } else {
> + return true;
> + }
> +}
> +NOKPROBE_SYMBOL(insns_are_not_simulated);
> +
> +static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb, int reenter)
> +{
> + if (reenter) {
> + save_previous_kprobe(kcb);
> + set_current_kprobe(p, regs, kcb);
> + kcb->kprobe_status = KPROBE_REENTER;
> + } else {
> + kcb->kprobe_status = KPROBE_HIT_SS;
> + }
> +
> + if (p->ainsn.insn->word == breakpoint_insn.word) {
> + regs->csr_prmd &= ~CSR_PRMD_PIE;
> + regs->csr_prmd |= kcb->kprobe_saved_irq;
> + return;
> + }
> +
> + regs->csr_prmd &= ~CSR_PRMD_PIE;
> +
> + if (insns_are_not_simulated(p, regs)) {
> + kcb->kprobe_status = KPROBE_HIT_SS;
> + regs->csr_era = (unsigned long)&p->ainsn.insn[0];
> + } else {
> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
> + if (p->post_handler)
> + p->post_handler(p, regs, 0);
> + reset_current_kprobe();
> + }
> +}
> +NOKPROBE_SYMBOL(setup_singlestep);
> +
> +static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb)
> +{
> + switch (kcb->kprobe_status) {
> + case KPROBE_HIT_SSDONE:
> + case KPROBE_HIT_ACTIVE:
> + kprobes_inc_nmissed_count(p);
> + setup_singlestep(p, regs, kcb, 1);
> + break;
> + case KPROBE_HIT_SS:
> + case KPROBE_REENTER:
> + pr_warn("Failed to recover from reentered kprobes.\n");
> + dump_kprobe(p);
> + BUG();
> + break;
> + default:
> + WARN_ON(1);
> + return false;
> + }
> +
> + return true;
> +}
> +NOKPROBE_SYMBOL(reenter_kprobe);
> +
> +static bool kprobe_pre_handler(struct pt_regs *regs)
> +{
> + struct kprobe *p, *cur_kprobe;
> + struct kprobe_ctlblk *kcb;
> + unsigned long addr = instruction_pointer(regs);
> +
> + kcb = get_kprobe_ctlblk();
> + cur_kprobe = kprobe_running();
> +
> + p = get_kprobe((kprobe_opcode_t *) addr);
> + if (p) {
> + if (cur_kprobe) {
> + if (reenter_kprobe(p, regs, kcb))
> + return true;
> + } else {
> + /* Probe hit */
> + set_current_kprobe(p, regs, kcb);
> + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +
> + /*
> + * If we have no pre-handler or it returned 0, we
> + * continue with normal processing. If we have a
> + * pre-handler and it returned non-zero, it will
> + * modify the execution path and no need to single
> + * stepping. Let's just reset current kprobe and exit.
> + *
> + * pre_handler can hit a breakpoint and can step thru
> + * before return.
> + */
> + if (!p->pre_handler || !p->pre_handler(p, regs))
> + setup_singlestep(p, regs, kcb, 0);
> + else
> + reset_current_kprobe();
> + }
> + return true;
> + }
> +
> + /*
> + * The breakpoint instruction was removed right
> + * after we hit it. Another cpu has removed
> + * either a probepoint or a debugger breakpoint
> + * at this address. In either case, no further
> + * handling of this interrupt is appropriate.
> + * Return back to original instruction, and continue.
> + */
> + return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_pre_handler);
> +
> +static bool kprobe_post_handler(struct pt_regs *regs)
> +{
> + struct kprobe *cur = kprobe_running();
> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> + if (!cur)
> + return false;
> +
> + /* Restore back the original saved kprobes variables and continue */
> + if (kcb->kprobe_status == KPROBE_REENTER) {
> + restore_previous_kprobe(kcb);
> + return true;
> + }
> +
> + /* Call post handler */
> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
> + if (cur->post_handler)
> + cur->post_handler(cur, regs, 0);
> +
> + regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
> + regs->csr_prmd |= kcb->kprobe_saved_irq;
> +
> + reset_current_kprobe();
> +
> + return true;
> +}
> +NOKPROBE_SYMBOL(kprobe_post_handler);
I'm not sure whether kprobe_pre_handler/kprobe_post_handler is
suitable, but nearly all other architectures use
kprobe_handler/post_kprobe_handler.
Huacai
> +
> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
> +{
> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> + if (kcb->kprobe_status & KPROBE_HIT_SS) {
> + regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
> + regs->csr_prmd |= kcb->kprobe_saved_irq;
> + reset_current_kprobe();
> + }
> +
> + return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_fault_handler);
> +
> +int kprobe_exceptions_notify(struct notifier_block *self,
> + unsigned long val, void *data)
> +{
> + struct die_args *args = (struct die_args *)data;
> + int ret = NOTIFY_DONE;
> +
> + switch (val) {
> + case DIE_BREAK:
> + if (kprobe_pre_handler(args->regs))
> + ret = NOTIFY_STOP;
> + break;
> + case DIE_SSTEPBP:
> + if (kprobe_post_handler(args->regs))
> + ret = NOTIFY_STOP;
> + break;
> + default:
> + break;
> + }
> +
> + return ret;
> +}
> +NOKPROBE_SYMBOL(kprobe_exceptions_notify);
> +
> +/*
> + * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
> + * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
> + */
> +int __init arch_populate_kprobe_blacklist(void)
> +{
> + return kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
> + (unsigned long)__irqentry_text_end);
> +}
> +
> +int __init arch_init_kprobes(void)
> +{
> + return 0;
> +}
> diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
> index 1ccd536..5882f17 100644
> --- a/arch/loongarch/mm/fault.c
> +++ b/arch/loongarch/mm/fault.c
> @@ -253,6 +253,9 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
> {
> irqentry_state_t state = irqentry_enter(regs);
>
> + if (kprobe_page_fault(regs, current->thread.trap_nr))
> + return;
> +
> /* Enable interrupt if enabled in parent context */
> if (likely(regs->csr_prmd & CSR_PRMD_PIE))
> local_irq_enable();
> --
> 2.1.0
>
>