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In-Reply-To: <1664326209-13995-3-git-send-email-yangtiezhu@loongson.cn>
From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Mon, 14 Nov 2022 12:41:42 +0800
Message-ID: <CAAhV-H4oj4NWO_AYQH5LWnASEtW9oyQnd_an=GCOB6QiZmc+sw@mail.gmail.com>
Subject: Re: [PATCH v2 2/5] LoongArch: Add kprobe support
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org
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Precedence: bulk

Hi, Tiezhu,

On Wed, Sep 28, 2022 at 8:50 AM Tiezhu Yang <yangtiezhu@loongson.cn> 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@loongson.cn>
> ---
>  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
>
>