Re: [PATCH v4 5/9] riscv: Add kprobes supported

Palmer Dabbelt
2020-11-06T01:02:26Z

On Sat, 17 Oct 2020 00:06:13 PDT (-0700), guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> This patch enables "kprobe & kretprobe" to work with ftrace
> interface. It utilized software breakpoint as single-step
> mechanism.
>
> Some instructions which can't be single-step executed must be
> simulated in kernel execution slot, such as: branch, jal, auipc,
> la ...
>
> Some instructions should be rejected for probing and we use a
> blacklist to filter, such as: ecall, ebreak, ...
>
> We use ebreak & c.ebreak to replace origin instruction and the
> kprobe handler prepares an executable memory slot for out-of-line
> execution with a copy of the original instruction being probed.
> In execution slot we add ebreak behind original instruction to
> simulate a single-setp mechanism.
>
> The patch is based on packi's work [1] and csky's work [2].
> - The kprobes_trampoline.S is all from packi's patch
> - The single-step mechanism is new designed for riscv without hw
> single-step trap
> - The simulation codes are from csky
> - Frankly, all codes refer to other archs' implementation
>
> [1] https://lore.kernel.org/linux-riscv/20181113195804.22825-1-me@packi.ch/
> [2] https://lore.kernel.org/linux-csky/20200403044150.20562-9-guoren@kernel.org/
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Co-Developed-by: Patrick Stählin <me@packi.ch>

Checkpatch says

WARNING: 'Co-developed-by:' is the preferred signature form
#108:
Co-Developed-by: Patrick Stählin <me@packi.ch>

WARNING: Co-developed-by: must be immediately followed by Signed-off-by:
#108:
Co-Developed-by: Patrick Stählin <me@packi.ch>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

There's some other checkpatch warnings throughout the patch set, but this is
one I'm not supposed to fix up. Can one of you re-post the patches with the
correct DCO?

> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
> Tested-by: Zong Li <zong.li@sifive.com>
> Reviewed-by: Pekka Enberg <penberg@kernel.org>
> Cc: Patrick Stählin <me@packi.ch>
> Cc: Palmer Dabbelt <palmerdabbelt@google.com>
> Cc: Björn Töpel <bjorn.topel@gmail.com>
> ---
> arch/riscv/Kconfig | 2 +
> arch/riscv/include/asm/kprobes.h | 40 +++
> arch/riscv/include/asm/probes.h | 24 ++
> arch/riscv/kernel/Makefile | 1 +
> arch/riscv/kernel/probes/Makefile | 4 +
> arch/riscv/kernel/probes/decode-insn.c | 48 ++++
> arch/riscv/kernel/probes/decode-insn.h | 18 ++
> arch/riscv/kernel/probes/kprobes.c | 398 ++++++++++++++++++++++++++
> arch/riscv/kernel/probes/kprobes_trampoline.S | 93 ++++++
> arch/riscv/kernel/probes/simulate-insn.c | 85 ++++++
> arch/riscv/kernel/probes/simulate-insn.h | 47 +++
> arch/riscv/kernel/traps.c | 9 +
> arch/riscv/mm/fault.c | 4 +
> 13 files changed, 773 insertions(+)
> create mode 100644 arch/riscv/include/asm/probes.h
> create mode 100644 arch/riscv/kernel/probes/Makefile
> create mode 100644 arch/riscv/kernel/probes/decode-insn.c
> create mode 100644 arch/riscv/kernel/probes/decode-insn.h
> create mode 100644 arch/riscv/kernel/probes/kprobes.c
> create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
> create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
> create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e6424d8b..c07214a 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -67,6 +67,8 @@ config RISCV
> select HAVE_FUTEX_CMPXCHG if FUTEX
> select HAVE_GCC_PLUGINS
> select HAVE_GENERIC_VDSO if MMU && 64BIT
> + select HAVE_KPROBES
> + select HAVE_KRETPROBES
> select HAVE_PCI
> select HAVE_PERF_EVENTS
> select HAVE_PERF_REGS
> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
> index 56a98ea3..4647d38 100644
> --- a/arch/riscv/include/asm/kprobes.h
> +++ b/arch/riscv/include/asm/kprobes.h
> @@ -11,4 +11,44 @@
>
> #include <asm-generic/kprobes.h>
>
> +#ifdef CONFIG_KPROBES
> +#include <linux/types.h>
> +#include <linux/ptrace.h>
> +#include <linux/percpu.h>
> +
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +#define MAX_INSN_SIZE 2
> +
> +#define flush_insn_slot(p) do { } while (0)
> +#define kretprobe_blacklist_size 0
> +
> +#include <asm/probes.h>
> +
> +struct prev_kprobe {
> + struct kprobe *kp;
> + unsigned int status;
> +};
> +
> +/* Single step context for kprobe */
> +struct kprobe_step_ctx {
> + unsigned long ss_pending;
> + unsigned long match_addr;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> + unsigned int kprobe_status;
> + unsigned long saved_status;
> + struct prev_kprobe prev_kprobe;
> + struct kprobe_step_ctx ss_ctx;
> +};
> +
> +void arch_remove_kprobe(struct kprobe *p);
> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr);
> +bool kprobe_breakpoint_handler(struct pt_regs *regs);
> +bool kprobe_single_step_handler(struct pt_regs *regs);
> +void kretprobe_trampoline(void);
> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
> +
> +#endif /* CONFIG_KPROBES */
> #endif /* _ASM_RISCV_KPROBES_H */
> diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
> new file mode 100644
> index 00000000..a787e6d
> --- /dev/null
> +++ b/arch/riscv/include/asm/probes.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _ASM_RISCV_PROBES_H
> +#define _ASM_RISCV_PROBES_H
> +
> +typedef u32 probe_opcode_t;
> +typedef bool (probes_handler_t) (u32 opcode, unsigned long addr, struct pt_regs *);
> +
> +/* architecture specific copy of original instruction */
> +struct arch_probe_insn {
> + probe_opcode_t *insn;
> + probes_handler_t *handler;
> + /* restore address after simulation */
> + unsigned long restore;
> +};
> +
> +#ifdef CONFIG_KPROBES
> +typedef u32 kprobe_opcode_t;
> +struct arch_specific_insn {
> + struct arch_probe_insn api;
> +};
> +#endif
> +
> +#endif /* _ASM_RISCV_PROBES_H */
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f14aed2..80958cb 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -29,6 +29,7 @@ obj-y += riscv_ksyms.o
> obj-y += stacktrace.o
> obj-y += cacheinfo.o
> obj-y += patch.o
> +obj-y += probes/
> obj-$(CONFIG_MMU) += vdso.o vdso/
>
> obj-$(CONFIG_RISCV_M_MODE) += traps_misaligned.o
> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
> new file mode 100644
> index 00000000..8a39507
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/Makefile
> @@ -0,0 +1,4 @@
> +# SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o simulate-insn.o
> +obj-$(CONFIG_KPROBES) += kprobes_trampoline.o
> +CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)
> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> new file mode 100644
> index 00000000..0876c30
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +#include <linux/module.h>
> +#include <linux/kallsyms.h>
> +#include <asm/sections.h>
> +
> +#include "decode-insn.h"
> +#include "simulate-insn.h"
> +
> +/* Return:
> + * INSN_REJECTED If instruction is one not allowed to kprobe,
> + * INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> + */
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
> +{
> + probe_opcode_t insn = le32_to_cpu(*addr);
> +
> + /*
> + * Reject instructions list:
> + */
> + RISCV_INSN_REJECTED(system, insn);
> + RISCV_INSN_REJECTED(fence, insn);
> +
> + /*
> + * Simulate instructions list:
> + * TODO: the REJECTED ones below need to be implemented
> + */
> +#ifdef CONFIG_RISCV_ISA_C
> + RISCV_INSN_REJECTED(c_j, insn);
> + RISCV_INSN_REJECTED(c_jr, insn);
> + RISCV_INSN_REJECTED(c_jal, insn);
> + RISCV_INSN_REJECTED(c_jalr, insn);
> + RISCV_INSN_REJECTED(c_beqz, insn);
> + RISCV_INSN_REJECTED(c_bnez, insn);
> + RISCV_INSN_REJECTED(c_ebreak, insn);
> +#endif
> +
> + RISCV_INSN_REJECTED(auipc, insn);
> + RISCV_INSN_REJECTED(branch, insn);
> +
> + RISCV_INSN_SET_SIMULATE(jal, insn);
> + RISCV_INSN_SET_SIMULATE(jalr, insn);
> +
> + return INSN_GOOD;
> +}
> diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
> new file mode 100644
> index 00000000..42269a7
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +
> +#include <asm/sections.h>
> +#include <asm/kprobes.h>
> +
> +enum probe_insn {
> + INSN_REJECTED,
> + INSN_GOOD_NO_SLOT,
> + INSN_GOOD,
> +};
> +
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *asi);
> +
> +#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> new file mode 100644
> index 00000000..e60893b
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -0,0 +1,398 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/kprobes.h>
> +#include <linux/extable.h>
> +#include <linux/slab.h>
> +#include <linux/stop_machine.h>
> +#include <asm/ptrace.h>
> +#include <linux/uaccess.h>
> +#include <asm/sections.h>
> +#include <asm/cacheflush.h>
> +#include <asm/bug.h>
> +#include <asm/patch.h>
> +
> +#include "decode-insn.h"
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
> +
> +static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
> +{
> + unsigned long offset = GET_INSN_LENGTH(p->opcode);
> +
> + p->ainsn.api.restore = (unsigned long)p->addr + offset;
> +
> + patch_text(p->ainsn.api.insn, p->opcode);
> + patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
> + __BUG_INSN_32);
> +}
> +
> +static void __kprobes arch_prepare_simulate(struct kprobe *p)
> +{
> + p->ainsn.api.restore = 0;
> +}
> +
> +static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
> +{
> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> + if (p->ainsn.api.handler)
> + p->ainsn.api.handler((u32)p->opcode,
> + (unsigned long)p->addr, regs);
> +
> + post_kprobe_handler(kcb, regs);
> +}
> +
> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
> +{
> + unsigned long probe_addr = (unsigned long)p->addr;
> +
> + if (probe_addr & 0x1) {
> + pr_warn("Address not aligned.\n");
> +
> + return -EINVAL;
> + }
> +
> + /* copy instruction */
> + p->opcode = le32_to_cpu(*p->addr);
> +
> + /* decode instruction */
> + switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
> + case INSN_REJECTED: /* insn not supported */
> + return -EINVAL;
> +
> + case INSN_GOOD_NO_SLOT: /* insn need simulation */
> + p->ainsn.api.insn = NULL;
> + break;
> +
> + case INSN_GOOD: /* instruction uses slot */
> + p->ainsn.api.insn = get_insn_slot();
> + if (!p->ainsn.api.insn)
> + return -ENOMEM;
> + break;
> + }
> +
> + /* prepare the instruction */
> + if (p->ainsn.api.insn)
> + arch_prepare_ss_slot(p);
> + else
> + arch_prepare_simulate(p);
> +
> + return 0;
> +}
> +
> +/* install breakpoint in text */
> +void __kprobes arch_arm_kprobe(struct kprobe *p)
> +{
> + if ((p->opcode & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
> + patch_text(p->addr, __BUG_INSN_32);
> + else
> + patch_text(p->addr, __BUG_INSN_16);
> +}
> +
> +/* remove breakpoint from text */
> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
> +{
> + patch_text(p->addr, p->opcode);
> +}
> +
> +void __kprobes arch_remove_kprobe(struct kprobe *p)
> +{
> +}
> +
> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> + kcb->prev_kprobe.kp = kprobe_running();
> + kcb->prev_kprobe.status = kcb->kprobe_status;
> +}
> +
> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> + __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> + kcb->kprobe_status = kcb->prev_kprobe.status;
> +}
> +
> +static void __kprobes set_current_kprobe(struct kprobe *p)
> +{
> + __this_cpu_write(current_kprobe, p);
> +}
> +
> +/*
> + * Interrupts need to be disabled before single-step mode is set, and not
> + * reenabled until after single-step mode ends.
> + * Without disabling interrupt on local CPU, there is a chance of
> + * interrupt occurrence in the period of exception return and start of
> + * out-of-line single-step, that result in wrongly single stepping
> + * into the interrupt handler.
> + */
> +static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
> + struct pt_regs *regs)
> +{
> + kcb->saved_status = regs->status;
> + regs->status &= ~SR_SPIE;
> +}
> +
> +static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
> + struct pt_regs *regs)
> +{
> + regs->status = kcb->saved_status;
> +}
> +
> +static void __kprobes
> +set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr, struct kprobe *p)
> +{
> + unsigned long offset = GET_INSN_LENGTH(p->opcode);
> +
> + kcb->ss_ctx.ss_pending = true;
> + kcb->ss_ctx.match_addr = addr + offset;
> +}
> +
> +static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
> +{
> + kcb->ss_ctx.ss_pending = false;
> + kcb->ss_ctx.match_addr = 0;
> +}
> +
> +static void __kprobes setup_singlestep(struct kprobe *p,
> + struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb, int reenter)
> +{
> + unsigned long slot;
> +
> + if (reenter) {
> + save_previous_kprobe(kcb);
> + set_current_kprobe(p);
> + kcb->kprobe_status = KPROBE_REENTER;
> + } else {
> + kcb->kprobe_status = KPROBE_HIT_SS;
> + }
> +
> + if (p->ainsn.api.insn) {
> + /* prepare for single stepping */
> + slot = (unsigned long)p->ainsn.api.insn;
> +
> + set_ss_context(kcb, slot, p); /* mark pending ss */
> +
> + /* IRQs and single stepping do not mix well. */
> + kprobes_save_local_irqflag(kcb, regs);
> +
> + instruction_pointer_set(regs, slot);
> + } else {
> + /* insn simulation */
> + arch_simulate_insn(p, regs);
> + }
> +}
> +
> +static int __kprobes 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("Unrecoverable kprobe detected.\n");
> + dump_kprobe(p);
> + BUG();
> + break;
> + default:
> + WARN_ON(1);
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
> +{
> + struct kprobe *cur = kprobe_running();
> +
> + if (!cur)
> + return;
> +
> + /* return addr restore if non-branching insn */
> + if (cur->ainsn.api.restore != 0)
> + regs->epc = cur->ainsn.api.restore;
> +
> + /* restore back original saved kprobe variables and continue */
> + if (kcb->kprobe_status == KPROBE_REENTER) {
> + restore_previous_kprobe(kcb);
> + return;
> + }
> +
> + /* call post handler */
> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
> + if (cur->post_handler) {
> + /* post_handler can hit breakpoint and single step
> + * again, so we enable D-flag for recursive exception.
> + */
> + cur->post_handler(cur, regs, 0);
> + }
> +
> + reset_current_kprobe();
> +}
> +
> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned 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->epc = (unsigned long) cur->addr;
> + if (!instruction_pointer(regs))
> + BUG();
> +
> + if (kcb->kprobe_status == KPROBE_REENTER)
> + restore_previous_kprobe(kcb);
> + else
> + reset_current_kprobe();
> +
> + break;
> + case KPROBE_HIT_ACTIVE:
> + case KPROBE_HIT_SSDONE:
> + /*
> + * We increment the nmissed count for accounting,
> + * we can also use npre/npostfault count for accounting
> + * these specific fault cases.
> + */
> + kprobes_inc_nmissed_count(cur);
> +
> + /*
> + * We come here because instructions in the pre/post
> + * handler caused the page_fault, this could happen
> + * if handler tries to access user space by
> + * copy_from_user(), get_user() etc. Let the
> + * user-specified handler try to fix it first.
> + */
> + if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
> + return 1;
> +
> + /*
> + * In case the user-specified fault handler returned
> + * zero, try to fix up.
> + */
> + if (fixup_exception(regs))
> + return 1;
> + }
> + return 0;
> +}
> +
> +bool __kprobes
> +kprobe_breakpoint_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);
> + 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;
> +}
> +
> +bool __kprobes
> +kprobe_single_step_handler(struct pt_regs *regs)
> +{
> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> + if ((kcb->ss_ctx.ss_pending)
> + && (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
> + clear_ss_context(kcb); /* clear pending ss */
> +
> + kprobes_restore_local_irqflag(kcb, regs);
> +
> + post_kprobe_handler(kcb, regs);
> + return true;
> + }
> + return false;
> +}
> +
> +/*
> + * 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)
> +{
> + int ret;
> +
> + ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
> + (unsigned long)__irqentry_text_end);
> + return ret;
> +}
> +
> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> +{
> + return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline, NULL);
> +}
> +
> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> + struct pt_regs *regs)
> +{
> + ri->ret_addr = (kprobe_opcode_t *)regs->ra;
> + ri->fp = NULL;
> + regs->ra = (unsigned long) &kretprobe_trampoline;
> +}
> +
> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
> +{
> + return 0;
> +}
> +
> +int __init arch_init_kprobes(void)
> +{
> + return 0;
> +}
> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> new file mode 100644
> index 00000000..6e85d02
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> @@ -0,0 +1,93 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Author: Patrick Stählin <me@packi.ch>
> + */
> +#include <linux/linkage.h>
> +
> +#include <asm/asm.h>
> +#include <asm/asm-offsets.h>
> +
> + .text
> + .altmacro
> +
> + .macro save_all_base_regs
> + REG_S x1, PT_RA(sp)
> + REG_S x3, PT_GP(sp)
> + REG_S x4, PT_TP(sp)
> + REG_S x5, PT_T0(sp)
> + REG_S x6, PT_T1(sp)
> + REG_S x7, PT_T2(sp)
> + REG_S x8, PT_S0(sp)
> + REG_S x9, PT_S1(sp)
> + REG_S x10, PT_A0(sp)
> + REG_S x11, PT_A1(sp)
> + REG_S x12, PT_A2(sp)
> + REG_S x13, PT_A3(sp)
> + REG_S x14, PT_A4(sp)
> + REG_S x15, PT_A5(sp)
> + REG_S x16, PT_A6(sp)
> + REG_S x17, PT_A7(sp)
> + REG_S x18, PT_S2(sp)
> + REG_S x19, PT_S3(sp)
> + REG_S x20, PT_S4(sp)
> + REG_S x21, PT_S5(sp)
> + REG_S x22, PT_S6(sp)
> + REG_S x23, PT_S7(sp)
> + REG_S x24, PT_S8(sp)
> + REG_S x25, PT_S9(sp)
> + REG_S x26, PT_S10(sp)
> + REG_S x27, PT_S11(sp)
> + REG_S x28, PT_T3(sp)
> + REG_S x29, PT_T4(sp)
> + REG_S x30, PT_T5(sp)
> + REG_S x31, PT_T6(sp)
> + .endm
> +
> + .macro restore_all_base_regs
> + REG_L x3, PT_GP(sp)
> + REG_L x4, PT_TP(sp)
> + REG_L x5, PT_T0(sp)
> + REG_L x6, PT_T1(sp)
> + REG_L x7, PT_T2(sp)
> + REG_L x8, PT_S0(sp)
> + REG_L x9, PT_S1(sp)
> + REG_L x10, PT_A0(sp)
> + REG_L x11, PT_A1(sp)
> + REG_L x12, PT_A2(sp)
> + REG_L x13, PT_A3(sp)
> + REG_L x14, PT_A4(sp)
> + REG_L x15, PT_A5(sp)
> + REG_L x16, PT_A6(sp)
> + REG_L x17, PT_A7(sp)
> + REG_L x18, PT_S2(sp)
> + REG_L x19, PT_S3(sp)
> + REG_L x20, PT_S4(sp)
> + REG_L x21, PT_S5(sp)
> + REG_L x22, PT_S6(sp)
> + REG_L x23, PT_S7(sp)
> + REG_L x24, PT_S8(sp)
> + REG_L x25, PT_S9(sp)
> + REG_L x26, PT_S10(sp)
> + REG_L x27, PT_S11(sp)
> + REG_L x28, PT_T3(sp)
> + REG_L x29, PT_T4(sp)
> + REG_L x30, PT_T5(sp)
> + REG_L x31, PT_T6(sp)
> + .endm
> +
> +ENTRY(kretprobe_trampoline)
> + addi sp, sp, -(PT_SIZE_ON_STACK)
> + save_all_base_regs
> +
> + move a0, sp /* pt_regs */
> +
> + call trampoline_probe_handler
> +
> + /* use the result as the return-address */
> + move ra, a0
> +
> + restore_all_base_regs
> + addi sp, sp, PT_SIZE_ON_STACK
> +
> + ret
> +ENDPROC(kretprobe_trampoline)
> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> new file mode 100644
> index 00000000..2519ce2
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/bitops.h>
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +
> +#include "decode-insn.h"
> +#include "simulate-insn.h"
> +
> +static inline bool rv_insn_reg_get_val(struct pt_regs *regs, u32 index,
> + unsigned long *ptr)
> +{
> + if (index == 0)
> + *ptr = 0;
> + else if (index <= 31)
> + *ptr = *((unsigned long *)regs + index);
> + else
> + return false;
> +
> + return true;
> +}
> +
> +static inline bool rv_insn_reg_set_val(struct pt_regs *regs, u32 index,
> + unsigned long val)
> +{
> + if (index == 0)
> + return false;
> + else if (index <= 31)
> + *((unsigned long *)regs + index) = val;
> + else
> + return false;
> +
> + return true;
> +}
> +
> +bool __kprobes simulate_jal(u32 opcode, unsigned long addr, struct pt_regs *regs)
> +{
> + /*
> + * 31 30 21 20 19 12 11 7 6 0
> + * imm [20] | imm[10:1] | imm[11] | imm[19:12] | rd | opcode
> + * 1 10 1 8 5 JAL/J
> + */
> + bool ret;
> + u32 imm;
> + u32 index = (opcode >> 7) & 0x1f;
> +
> + ret = rv_insn_reg_set_val(regs, index, addr + 4);
> + if (!ret)
> + return ret;
> +
> + imm = ((opcode >> 21) & 0x3ff) << 1;
> + imm |= ((opcode >> 20) & 0x1) << 11;
> + imm |= ((opcode >> 12) & 0xff) << 12;
> + imm |= ((opcode >> 31) & 0x1) << 20;
> +
> + instruction_pointer_set(regs, addr + sign_extend32((imm), 20));
> +
> + return ret;
> +}
> +
> +bool __kprobes simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs)
> +{
> + /*
> + * 31 20 19 15 14 12 11 7 6 0
> + * offset[11:0] | rs1 | 010 | rd | opcode
> + * 12 5 3 5 JALR/JR
> + */
> + bool ret;
> + unsigned long base_addr;
> + u32 imm = (opcode >> 20) & 0xfff;
> + u32 rd_index = (opcode >> 7) & 0x1f;
> + u32 rs1_index = (opcode >> 15) & 0x1f;
> +
> + ret = rv_insn_reg_set_val(regs, rd_index, addr + 4);
> + if (!ret)
> + return ret;
> +
> + ret = rv_insn_reg_get_val(regs, rs1_index, &base_addr);
> + if (!ret)
> + return ret;
> +
> + instruction_pointer_set(regs, (base_addr + sign_extend32((imm), 11))&~1);
> +
> + return ret;
> +}
> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> new file mode 100644
> index 00000000..a62d784
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#ifndef _RISCV_KERNEL_PROBES_SIMULATE_INSN_H
> +#define _RISCV_KERNEL_PROBES_SIMULATE_INSN_H
> +
> +#define __RISCV_INSN_FUNCS(name, mask, val) \
> +static __always_inline bool riscv_insn_is_##name(probe_opcode_t code) \
> +{ \
> + BUILD_BUG_ON(~(mask) & (val)); \
> + return (code & (mask)) == (val); \
> +} \
> +bool simulate_##name(u32 opcode, unsigned long addr, \
> + struct pt_regs *regs);
> +
> +#define RISCV_INSN_REJECTED(name, code) \
> + do { \
> + if (riscv_insn_is_##name(code)) { \
> + return INSN_REJECTED; \
> + } \
> + } while (0)
> +
> +__RISCV_INSN_FUNCS(system, 0x7f, 0x73)
> +__RISCV_INSN_FUNCS(fence, 0x7f, 0x0f)
> +
> +#define RISCV_INSN_SET_SIMULATE(name, code) \
> + do { \
> + if (riscv_insn_is_##name(code)) { \
> + api->handler = simulate_##name; \
> + return INSN_GOOD_NO_SLOT; \
> + } \
> + } while (0)
> +
> +__RISCV_INSN_FUNCS(c_j, 0xe003, 0xa001)
> +__RISCV_INSN_FUNCS(c_jr, 0xf007, 0x8002)
> +__RISCV_INSN_FUNCS(c_jal, 0xe003, 0x2001)
> +__RISCV_INSN_FUNCS(c_jalr, 0xf007, 0x9002)
> +__RISCV_INSN_FUNCS(c_beqz, 0xe003, 0xc001)
> +__RISCV_INSN_FUNCS(c_bnez, 0xe003, 0xe001)
> +__RISCV_INSN_FUNCS(c_ebreak, 0xffff, 0x9002)
> +
> +__RISCV_INSN_FUNCS(auipc, 0x7f, 0x17)
> +__RISCV_INSN_FUNCS(branch, 0x7f, 0x63)
> +
> +__RISCV_INSN_FUNCS(jal, 0x7f, 0x6f)
> +__RISCV_INSN_FUNCS(jalr, 0x707f, 0x67)
> +
> +#endif /* _RISCV_KERNEL_PROBES_SIMULATE_INSN_H */
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index ad14f44..19a788a 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -12,6 +12,7 @@
> #include <linux/signal.h>
> #include <linux/kdebug.h>
> #include <linux/uaccess.h>
> +#include <linux/kprobes.h>
> #include <linux/mm.h>
> #include <linux/module.h>
> #include <linux/irq.h>
> @@ -145,6 +146,14 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
>
> asmlinkage __visible void do_trap_break(struct pt_regs *regs)
> {
> +#ifdef CONFIG_KPROBES
> + if (kprobe_single_step_handler(regs))
> + return;
> +
> + if (kprobe_breakpoint_handler(regs))
> + return;
> +#endif
> +
> if (user_mode(regs))
> force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
> #ifdef CONFIG_KGDB
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 716d64e..6afd59d 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -13,6 +13,7 @@
> #include <linux/perf_event.h>
> #include <linux/signal.h>
> #include <linux/uaccess.h>
> +#include <linux/kprobes.h>
>
> #include <asm/ptrace.h>
> #include <asm/tlbflush.h>
> @@ -39,6 +40,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
> tsk = current;
> mm = tsk->mm;
>
> + if (kprobe_page_fault(regs, cause))
> + return;
> +
> /*
> * Fault-in kernel-space virtual memory on-demand.
> * The 'reference' page table is init_mm.pgd.