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From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     Huacai Chen <chenhuacai@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: [PATCH 1/4] LoongArch: Add kprobe support
Date:   Tue, 20 Sep 2022 11:37:11 +0800
Message-Id: <1663645034-967-2-git-send-email-yangtiezhu@loongson.cn>
In-Reply-To: <1663645034-967-1-git-send-email-yangtiezhu@loongson.cn>
References: <1663645034-967-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

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    |  31 ++++
 arch/loongarch/include/asm/kprobes.h |  44 +++++
 arch/loongarch/include/asm/ptrace.h  |   1 +
 arch/loongarch/kernel/Makefile       |   2 +
 arch/loongarch/kernel/inst.c         | 107 ++++++++++++
 arch/loongarch/kernel/kprobes.c      | 309 +++++++++++++++++++++++++++++++++++
 7 files changed, 495 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 5b5fc94..6b01073 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 fce1843..fc8879b 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -7,6 +7,7 @@
 
 #include <linux/types.h>
 #include <asm/asm.h>
+#include <asm/ptrace.h>
 
 #define INSN_BREAK		0x002a0000
 
@@ -20,6 +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,
@@ -28,6 +33,8 @@ enum reg0i26_op {
 enum reg1i20_op {
 	lu12iw_op	= 0x0a,
 	lu32id_op	= 0x0b,
+	pcaddi_op	= 0x0c,
+	pcalau12i_op	= 0x0d,
 	pcaddu12i_op	= 0x0e,
 	pcaddu18i_op	= 0x0f,
 };
@@ -35,6 +42,8 @@ enum reg1i20_op {
 enum reg1i21_op {
 	beqz_op		= 0x10,
 	bnez_op		= 0x11,
+	bceqz_op	= 0x48000000,
+	bcnez_op	= 0x48000100,
 };
 
 enum reg2_op {
@@ -164,6 +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;
@@ -249,6 +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;
@@ -313,6 +328,12 @@ static inline bool is_branch_ins(union loongarch_instruction *ip)
 		ip->reg1i21_format.opcode <= bgeu_op;
 }
 
+static inline bool is_pc_ins(union loongarch_instruction *ip)
+{
+	return ip->reg1i20_format.opcode >= pcaddi_op &&
+		ip->reg1i20_format.opcode <= pcaddu18i_op;
+}
+
 static inline bool is_ra_save_ins(union loongarch_instruction *ip)
 {
 	/* st.d $ra, $sp, offset */
@@ -334,6 +355,16 @@ static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
 u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
 u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
 u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
+void simu_branch(struct pt_regs *regs, union loongarch_instruction insn);
+void simu_pc(struct pt_regs *regs, union loongarch_instruction insn);
+
+static inline unsigned long sign_extended(unsigned long val, unsigned int idx)
+{
+	if (val & (1UL << idx))
+		return ~((1UL << (idx + 1)) - 1) | val;
+	else
+		return ((1UL << (idx + 1)) - 1) & val;
+}
 
 static inline bool signed_imm_check(long val, unsigned int bit)
 {
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)
+#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/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
index 17838c6..eb9538a 100644
--- a/arch/loongarch/include/asm/ptrace.h
+++ b/arch/loongarch/include/asm/ptrace.h
@@ -6,6 +6,7 @@
 #define _ASM_PTRACE_H
 
 #include <asm/page.h>
+#include <asm/irqflags.h>
 #include <asm/thread_info.h>
 #include <uapi/asm/ptrace.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/inst.c b/arch/loongarch/kernel/inst.c
index b1df0ec..143acb6 100644
--- a/arch/loongarch/kernel/inst.c
+++ b/arch/loongarch/kernel/inst.c
@@ -38,3 +38,110 @@ u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned l
 
 	return insn.word;
 }
+
+void simu_branch(struct pt_regs *regs, union loongarch_instruction insn)
+{
+	unsigned int imm, imm_l, imm_h, rd, rj;
+	unsigned long pc = regs->csr_era;
+
+	imm_l = insn.reg0i26_format.immediate_l;
+	imm_h = insn.reg0i26_format.immediate_h;
+	switch (insn.reg0i26_format.opcode) {
+	case b_op:
+		regs->csr_era = pc + sign_extended((imm_h << 16 | imm_l) << 2, 27);
+		return;
+	case bl_op:
+		regs->csr_era = pc + sign_extended((imm_h << 16 | imm_l) << 2, 27);
+		regs->regs[1] = pc + LOONGARCH_INSN_SIZE;
+		return;
+	}
+
+	imm_l = insn.reg1i21_format.immediate_l;
+	imm_h = insn.reg1i21_format.immediate_h;
+	rj = insn.reg1i21_format.rj;
+	switch (insn.reg1i21_format.opcode) {
+	case beqz_op:
+		if (regs->regs[rj] == 0)
+			regs->csr_era = pc + sign_extended((imm_h << 16 | imm_l) << 2, 22);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		return;
+	case bnez_op:
+		if (regs->regs[rj] != 0)
+			regs->csr_era = pc + sign_extended((imm_h << 16 | imm_l) << 2, 22);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		return;
+	}
+
+	imm = insn.reg2i16_format.immediate;
+	rj = insn.reg2i16_format.rj;
+	rd = insn.reg2i16_format.rd;
+	switch (insn.reg2i16_format.opcode) {
+	case beq_op:
+		if (regs->regs[rj] == regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case bne_op:
+		if (regs->regs[rj] != regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case blt_op:
+		if ((long)regs->regs[rj] < (long)regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case bge_op:
+		if ((long)regs->regs[rj] >= (long)regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case bltu_op:
+		if (regs->regs[rj] < regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case bgeu_op:
+		if (regs->regs[rj] >= regs->regs[rd])
+			regs->csr_era = pc + sign_extended(imm << 2, 17);
+		else
+			regs->csr_era = pc + LOONGARCH_INSN_SIZE;
+		break;
+	case jirl_op:
+		regs->csr_era = regs->regs[rj] + sign_extended(imm << 2, 17);
+		regs->regs[rd] = pc + LOONGARCH_INSN_SIZE;
+		break;
+	}
+}
+
+void simu_pc(struct pt_regs *regs, union loongarch_instruction insn)
+{
+	unsigned long pc = regs->csr_era;
+	unsigned int rd = insn.reg1i20_format.rd;
+	unsigned int imm = insn.reg1i20_format.immediate;
+
+	switch (insn.reg1i20_format.opcode) {
+	case pcaddi_op:
+		regs->regs[rd] = pc + sign_extended(imm << 2, 21);
+		break;
+	case pcaddu12i_op:
+		regs->regs[rd] = pc + sign_extended(imm << 12, 31);
+		break;
+	case pcaddu18i_op:
+		regs->regs[rd] = pc + sign_extended(imm << 18, 37);
+		break;
+	case pcalau12i_op:
+		regs->regs[rd] = pc + sign_extended(imm << 12, 31);
+		regs->regs[rd] &= ~((1 << 12) - 1);
+		break;
+	}
+
+	regs->csr_era += LOONGARCH_INSN_SIZE;
+}
diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
new file mode 100644
index 0000000..b2c73a5
--- /dev/null
+++ b/arch/loongarch/kernel/kprobes.c
@@ -0,0 +1,309 @@
+// 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 inline 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);
+
+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;
+	case DIE_PAGE_FAULT:
+		preempt_disable();
+		if (kprobe_running()
+		    && kprobe_fault_handler(args->regs, args->trapnr))
+			ret = NOTIFY_STOP;
+		preempt_enable();
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+NOKPROBE_SYMBOL(kprobe_exceptions_notify);
+
+int __init arch_init_kprobes(void)
+{
+	return 0;
+}
-- 
2.1.0