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Subject: Re: [PATCH v9 2/4] LoongArch: Add kprobe support
To:     Huacai Chen <chenhuacai@kernel.org>,
        Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
References: <1670506868-15771-1-git-send-email-yangtiezhu@loongson.cn>
 <1670506868-15771-3-git-send-email-yangtiezhu@loongson.cn>
 <CAAhV-H54yruHAe7ey8L9hHPonryEWEd8nt-iS6s7-odrDdrutw@mail.gmail.com>
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <b1b4614c-7d7f-0773-dced-9182a510a80a@loongson.cn>
Date:   Fri, 9 Dec 2022 11:31:21 +0800
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On 2022-12-09 10:22, Huacai Chen wrote:

>    cas
>
> On Thu, Dec 8, 2022 at 9:41 PM 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    |  15 ++
>>   arch/loongarch/include/asm/kprobes.h |  59 +++++++
>>   arch/loongarch/kernel/Makefile       |   2 +
>>   arch/loongarch/kernel/kprobes.c      | 332 +++++++++++++++++++++++++++++++++++
>>   arch/loongarch/kernel/traps.c        |  13 +-
>>   arch/loongarch/mm/fault.c            |   3 +
>>   7 files changed, 421 insertions(+), 4 deletions(-)
>>   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 16bf1b6..f6fc156 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -102,6 +102,7 @@ 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 19cf692..e3f2378 100644
>> --- a/arch/loongarch/include/asm/inst.h
>> +++ b/arch/loongarch/include/asm/inst.h
>> @@ -24,6 +24,10 @@
>>
>>   #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,
>> @@ -180,6 +184,11 @@ 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;
>> @@ -265,6 +274,7 @@ 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;
>> @@ -335,6 +345,11 @@ static inline bool is_branch_ins(union loongarch_instruction *ip)
>>                  ip->reg1i21_format.opcode <= bgeu_op;
>>   }
>>
>> +static inline bool is_break_ins(union loongarch_instruction *ip)
>> +{
>> +       return ip->reg0i15_format.opcode == break_op;
>> +}
>> +
>>   static inline bool is_ra_save_ins(union loongarch_instruction *ip)
>>   {
>>          /* st.d $ra, $sp, offset */
>> diff --git a/arch/loongarch/include/asm/kprobes.h b/arch/loongarch/include/asm/kprobes.h
>> new file mode 100644
>> index 0000000..d3903f3
>> --- /dev/null
>> +++ b/arch/loongarch/include/asm/kprobes.h
>> @@ -0,0 +1,59 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +#ifndef __ASM_LOONGARCH_KPROBES_H
>> +#define __ASM_LOONGARCH_KPROBES_H
>> +
>> +#include <asm-generic/kprobes.h>
>> +#include <asm/cacheflush.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 {                                                                   \
>> +       if (p->addr)                                                    \
>> +               flush_icache_range((unsigned long)p->addr,              \
>> +                          (unsigned long)p->addr +                     \
>> +                          (MAX_INSN_SIZE * sizeof(kprobe_opcode_t)));  \
>> +} while (0)
>> +
>> +#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);
>> +bool kprobe_breakpoint_handler(struct pt_regs *regs);
>> +bool kprobe_singlestep_handler(struct pt_regs *regs);
>> +
>> +#else /* !CONFIG_KPROBES */
>> +
>> +static inline bool kprobe_breakpoint_handler(struct pt_regs *regs) { return 0; }
>> +static inline bool kprobe_singlestep_handler(struct pt_regs *regs) { return 0; }
>> +
>> +#endif /* CONFIG_KPROBES */
>> +#endif /* __ASM_LOONGARCH_KPROBES_H */
>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
>> index fcaa024..6fe4a4e 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -47,4 +47,6 @@ 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..aadfc9ae
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/kprobes.c
>> @@ -0,0 +1,332 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +#include <linux/kprobes.h>
>> +#include <linux/kdebug.h>
>> +#include <linux/preempt.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)
> Use  insns_not_supported for short.
>
>> +{
>> +       switch (insn.reg2i14_format.opcode) {
>> +       case llw_op:
>> +       case lld_op:
>> +       case scw_op:
>> +       case scd_op:
>> +               pr_notice("kprobe: ll and sc instructions are not supported\n");
>> +               return true;
>> +       }
>> +
>> +       switch (insn.reg1i21_format.opcode) {
>> +       case bceqz_op:
>> +               pr_notice("kprobe: bceqz and 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;
>> +       flush_insn_slot(p);
>> +}
>> +NOKPROBE_SYMBOL(arch_arm_kprobe);
>> +
>> +/* Remove breakpoint from text */
>> +void arch_disarm_kprobe(struct kprobe *p)
>> +{
>> +       *p->addr = p->opcode;
>> +       flush_insn_slot(p);
>> +}
>> +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)
> Use  insns_not_simulated for short.
>> +{
>> +       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;
>> +       }
>> +
>> +       regs->csr_prmd &= ~CSR_PRMD_PIE;
>> +
>> +       if (p->ainsn.insn->word == breakpoint_insn.word) {
>> +               regs->csr_prmd |= kcb->kprobe_saved_irq;
>> +               preempt_enable_no_resched();
>> +               return;
>> +       }
>> +
>> +       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();
>> +               preempt_enable_no_resched();
>> +       }
>> +}
>> +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);
>> +
>> +bool kprobe_breakpoint_handler(struct pt_regs *regs)
>> +{
>> +       struct kprobe_ctlblk *kcb;
>> +       struct kprobe *p, *cur_kprobe;
>> +       kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->csr_era;
>> +
>> +       /*
>> +        * We don't want to be preempted for the entire
>> +        * duration of kprobe processing.
>> +        */
>> +       preempt_disable();
>> +       kcb = get_kprobe_ctlblk();
>> +       cur_kprobe = kprobe_running();
>> +
>> +       p = get_kprobe(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();
>> +                               preempt_enable_no_resched();
>> +                       }
>> +               }
>> +               return true;
>> +       }
>> +
>> +       if (!is_break_ins(addr)) {
>> +               /*
>> +                * 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.
>> +                */
>> +               preempt_enable_no_resched();
>> +               return true;
>> +       }
>> +
>> +       preempt_enable_no_resched();
>> +       return false;
>> +}
>> +NOKPROBE_SYMBOL(kprobe_breakpoint_handler);
>> +
>> +bool kprobe_singlestep_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);
>> +               goto out;
>> +       }
>> +
>> +       /* Call post handler */
>> +       kcb->kprobe_status = KPROBE_HIT_SSDONE;
>> +       if (cur->post_handler)
>> +               cur->post_handler(cur, regs, 0);
> I'm not very familiar, but I think you should set KPROBE_HIT_SSDONE
> only when post_handler is not NULL.
>
>> +
>> +       regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
>> +       regs->csr_prmd |= kcb->kprobe_saved_irq;
>> +
>> +       reset_current_kprobe();
>> +out:
>> +       preempt_enable_no_resched();
>> +       return true;
>> +}
>> +NOKPROBE_SYMBOL(kprobe_singlestep_handler);
>> +
>> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
>> +{
>> +       struct kprobe *cur = kprobe_running();
>> +       struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +
>> +       switch (kcb->kprobe_status) {
>> +       case KPROBE_HIT_SS:
>> +       case KPROBE_REENTER:
>> +               /*
>> +                * We are here because the instruction being single
>> +                * stepped caused a page fault. We reset the current
>> +                * kprobe and the ip points back to the probe address
>> +                * and allow the page fault handler to continue as a
>> +                * normal page fault.
>> +                */
>> +               regs->csr_era = (unsigned long) cur->addr;
>> +               BUG_ON(!instruction_pointer(regs));
>> +
>> +               if (kcb->kprobe_status == KPROBE_REENTER) {
>> +                       restore_previous_kprobe(kcb);
>> +               } else {
>> +                       regs->csr_prmd |= kcb->kprobe_saved_irq;
>> +                       reset_current_kprobe();
>> +                       preempt_enable_no_resched();
>> +               }
> I think the KPROBE_REENTER case also needs to enable preemption.
>
>> +
>> +               break;
>> +       case KPROBE_HIT_ACTIVE:
>> +       case KPROBE_HIT_SSDONE:
>> +               /*
>> +                * In case the user-specified fault handler returned
>> +                * zero, try to fix up.
>> +                */
>> +               if (fixup_exception(regs))
>> +                       return true;
> Does here need to enable preemption too?
>
>> +       }
>> +       return false;
>> +}
>> +NOKPROBE_SYMBOL(kprobe_fault_handler);
>> +
>> +/*
>> + * 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/kernel/traps.c b/arch/loongarch/kernel/traps.c
>> index a19bb32..4d9f775 100644
>> --- a/arch/loongarch/kernel/traps.c
>> +++ b/arch/loongarch/kernel/traps.c
>> @@ -448,14 +448,12 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>>           */
>>          switch (bcode) {
>>          case BRK_KPROBE_BP:
>> -               if (notify_die(DIE_BREAK, "Kprobe", regs, bcode,
>> -                              current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
>> +               if (kprobe_breakpoint_handler(regs))
>>                          goto out;
>>                  else
>>                          break;
>>          case BRK_KPROBE_SSTEPBP:
>> -               if (notify_die(DIE_SSTEPBP, "Kprobe_SingleStep", regs, bcode,
>> -                              current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
>> +               if (kprobe_singlestep_handler(regs))
>>                          goto out;
>>                  else
>>                          break;
>> @@ -479,6 +477,13 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>>                          break;
>>          }
>>
>> +       if (bcode == BRK_KPROBE_BP) {
>> +               if (__get_inst(&opcode, (u32 *)era, user))
>> +                       goto out_sigsegv;
>> +
>> +               bcode = (opcode & 0x7fff);
>> +       }
>> +
> Why? we already got bcode at the beginning.

Hi, Huacai,


I think it is because kprobe_breakpoint_handler() may deal with that 
case other cpu may remove its breakpoint. In that case, normally we can 
exit this break exception and go on. But if
the orignal instruction is_break_ins(), we will trigger trap aggain. So 
it is better to avoid double traps and let it go ahead when 
kprobe_breakpoint_handler() returns.
Differnt from many other archs, e.g. riscv, we switch bcode to decide 
which handlers should go on. Thus, we need get bcode again.

Thanks,

Jinyang


>>          switch (bcode) {
>>          case BRK_BUG:
>>                  bug_handler(regs);
>> diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
>> index 1ccd536..449087b 100644
>> --- a/arch/loongarch/mm/fault.c
>> +++ b/arch/loongarch/mm/fault.c
>> @@ -135,6 +135,9 @@ static void __kprobes __do_page_fault(struct pt_regs *regs,
>>          struct vm_area_struct *vma = NULL;
>>          vm_fault_t fault;
>>
>> +       if (kprobe_page_fault(regs, current->thread.trap_nr))
>> +               return;
>> +
>>          /*
>>           * We fault-in kernel-space virtual memory on-demand. The
>>           * 'reference' page table is init_mm.pgd.
>> --
>> 2.1.0
>>
>>