1 files changed, 460 insertions, 0 deletions
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
new file mode 100644
index 000000000..64f2ecbdf
--- /dev/null
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -0,0 +1,460 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ARMv8 single-step debug support and mdscr context switching.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+#include <linux/cpu.h>
+#include <linux/debugfs.h>
+#include <linux/hardirq.h>
+#include <linux/init.h>
+#include <linux/ptrace.h>
+#include <linux/kprobes.h>
+#include <linux/stat.h>
+#include <linux/uaccess.h>
+#include <linux/sched/task_stack.h>
+
+#include <asm/cpufeature.h>
+#include <asm/cputype.h>
+#include <asm/daifflags.h>
+#include <asm/debug-monitors.h>
+#include <asm/system_misc.h>
+#include <asm/traps.h>
+
+/* Determine debug architecture. */
+u8 debug_monitors_arch(void)
+{
+	return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
+						ID_AA64DFR0_EL1_DebugVer_SHIFT);
+}
+
+/*
+ * MDSCR access routines.
+ */
+static void mdscr_write(u32 mdscr)
+{
+	unsigned long flags;
+	flags = local_daif_save();
+	write_sysreg(mdscr, mdscr_el1);
+	local_daif_restore(flags);
+}
+NOKPROBE_SYMBOL(mdscr_write);
+
+static u32 mdscr_read(void)
+{
+	return read_sysreg(mdscr_el1);
+}
+NOKPROBE_SYMBOL(mdscr_read);
+
+/*
+ * Allow root to disable self-hosted debug from userspace.
+ * This is useful if you want to connect an external JTAG debugger.
+ */
+static bool debug_enabled = true;
+
+static int create_debug_debugfs_entry(void)
+{
+	debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
+	return 0;
+}
+fs_initcall(create_debug_debugfs_entry);
+
+static int __init early_debug_disable(char *buf)
+{
+	debug_enabled = false;
+	return 0;
+}
+
+early_param("nodebugmon", early_debug_disable);
+
+/*
+ * Keep track of debug users on each core.
+ * The ref counts are per-cpu so we use a local_t type.
+ */
+static DEFINE_PER_CPU(int, mde_ref_count);
+static DEFINE_PER_CPU(int, kde_ref_count);
+
+void enable_debug_monitors(enum dbg_active_el el)
+{
+	u32 mdscr, enable = 0;
+
+	WARN_ON(preemptible());
+
+	if (this_cpu_inc_return(mde_ref_count) == 1)
+		enable = DBG_MDSCR_MDE;
+
+	if (el == DBG_ACTIVE_EL1 &&
+	    this_cpu_inc_return(kde_ref_count) == 1)
+		enable |= DBG_MDSCR_KDE;
+
+	if (enable && debug_enabled) {
+		mdscr = mdscr_read();
+		mdscr |= enable;
+		mdscr_write(mdscr);
+	}
+}
+NOKPROBE_SYMBOL(enable_debug_monitors);
+
+void disable_debug_monitors(enum dbg_active_el el)
+{
+	u32 mdscr, disable = 0;
+
+	WARN_ON(preemptible());
+
+	if (this_cpu_dec_return(mde_ref_count) == 0)
+		disable = ~DBG_MDSCR_MDE;
+
+	if (el == DBG_ACTIVE_EL1 &&
+	    this_cpu_dec_return(kde_ref_count) == 0)
+		disable &= ~DBG_MDSCR_KDE;
+
+	if (disable) {
+		mdscr = mdscr_read();
+		mdscr &= disable;
+		mdscr_write(mdscr);
+	}
+}
+NOKPROBE_SYMBOL(disable_debug_monitors);
+
+/*
+ * OS lock clearing.
+ */
+static int clear_os_lock(unsigned int cpu)
+{
+	write_sysreg(0, osdlr_el1);
+	write_sysreg(0, oslar_el1);
+	isb();
+	return 0;
+}
+
+static int __init debug_monitors_init(void)
+{
+	return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
+				 "arm64/debug_monitors:starting",
+				 clear_os_lock, NULL);
+}
+postcore_initcall(debug_monitors_init);
+
+/*
+ * Single step API and exception handling.
+ */
+static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
+{
+	regs->pstate |= DBG_SPSR_SS;
+}
+NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
+
+static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
+{
+	regs->pstate &= ~DBG_SPSR_SS;
+}
+NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
+
+#define set_regs_spsr_ss(r)	set_user_regs_spsr_ss(&(r)->user_regs)
+#define clear_regs_spsr_ss(r)	clear_user_regs_spsr_ss(&(r)->user_regs)
+
+static DEFINE_SPINLOCK(debug_hook_lock);
+static LIST_HEAD(user_step_hook);
+static LIST_HEAD(kernel_step_hook);
+
+static void register_debug_hook(struct list_head *node, struct list_head *list)
+{
+	spin_lock(&debug_hook_lock);
+	list_add_rcu(node, list);
+	spin_unlock(&debug_hook_lock);
+
+}
+
+static void unregister_debug_hook(struct list_head *node)
+{
+	spin_lock(&debug_hook_lock);
+	list_del_rcu(node);
+	spin_unlock(&debug_hook_lock);
+	synchronize_rcu();
+}
+
+void register_user_step_hook(struct step_hook *hook)
+{
+	register_debug_hook(&hook->node, &user_step_hook);
+}
+
+void unregister_user_step_hook(struct step_hook *hook)
+{
+	unregister_debug_hook(&hook->node);
+}
+
+void register_kernel_step_hook(struct step_hook *hook)
+{
+	register_debug_hook(&hook->node, &kernel_step_hook);
+}
+
+void unregister_kernel_step_hook(struct step_hook *hook)
+{
+	unregister_debug_hook(&hook->node);
+}
+
+/*
+ * Call registered single step handlers
+ * There is no Syndrome info to check for determining the handler.
+ * So we call all the registered handlers, until the right handler is
+ * found which returns zero.
+ */
+static int call_step_hook(struct pt_regs *regs, unsigned long esr)
+{
+	struct step_hook *hook;
+	struct list_head *list;
+	int retval = DBG_HOOK_ERROR;
+
+	list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
+
+	/*
+	 * Since single-step exception disables interrupt, this function is
+	 * entirely not preemptible, and we can use rcu list safely here.
+	 */
+	list_for_each_entry_rcu(hook, list, node)	{
+		retval = hook->fn(regs, esr);
+		if (retval == DBG_HOOK_HANDLED)
+			break;
+	}
+
+	return retval;
+}
+NOKPROBE_SYMBOL(call_step_hook);
+
+static void send_user_sigtrap(int si_code)
+{
+	struct pt_regs *regs = current_pt_regs();
+
+	if (WARN_ON(!user_mode(regs)))
+		return;
+
+	if (interrupts_enabled(regs))
+		local_irq_enable();
+
+	arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs),
+			      "User debug trap");
+}
+
+static int single_step_handler(unsigned long unused, unsigned long esr,
+			       struct pt_regs *regs)
+{
+	bool handler_found = false;
+
+	/*
+	 * If we are stepping a pending breakpoint, call the hw_breakpoint
+	 * handler first.
+	 */
+	if (!reinstall_suspended_bps(regs))
+		return 0;
+
+	if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
+		handler_found = true;
+
+	if (!handler_found && user_mode(regs)) {
+		send_user_sigtrap(TRAP_TRACE);
+
+		/*
+		 * ptrace will disable single step unless explicitly
+		 * asked to re-enable it. For other clients, it makes
+		 * sense to leave it enabled (i.e. rewind the controls
+		 * to the active-not-pending state).
+		 */
+		user_rewind_single_step(current);
+	} else if (!handler_found) {
+		pr_warn("Unexpected kernel single-step exception at EL1\n");
+		/*
+		 * Re-enable stepping since we know that we will be
+		 * returning to regs.
+		 */
+		set_regs_spsr_ss(regs);
+	}
+
+	return 0;
+}
+NOKPROBE_SYMBOL(single_step_handler);
+
+static LIST_HEAD(user_break_hook);
+static LIST_HEAD(kernel_break_hook);
+
+void register_user_break_hook(struct break_hook *hook)
+{
+	register_debug_hook(&hook->node, &user_break_hook);
+}
+
+void unregister_user_break_hook(struct break_hook *hook)
+{
+	unregister_debug_hook(&hook->node);
+}
+
+void register_kernel_break_hook(struct break_hook *hook)
+{
+	register_debug_hook(&hook->node, &kernel_break_hook);
+}
+
+void unregister_kernel_break_hook(struct break_hook *hook)
+{
+	unregister_debug_hook(&hook->node);
+}
+
+static int call_break_hook(struct pt_regs *regs, unsigned long esr)
+{
+	struct break_hook *hook;
+	struct list_head *list;
+	int (*fn)(struct pt_regs *regs, unsigned long esr) = NULL;
+
+	list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
+
+	/*
+	 * Since brk exception disables interrupt, this function is
+	 * entirely not preemptible, and we can use rcu list safely here.
+	 */
+	list_for_each_entry_rcu(hook, list, node) {
+		unsigned long comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
+
+		if ((comment & ~hook->mask) == hook->imm)
+			fn = hook->fn;
+	}
+
+	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
+}
+NOKPROBE_SYMBOL(call_break_hook);
+
+static int brk_handler(unsigned long unused, unsigned long esr,
+		       struct pt_regs *regs)
+{
+	if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
+		return 0;
+
+	if (user_mode(regs)) {
+		send_user_sigtrap(TRAP_BRKPT);
+	} else {
+		pr_warn("Unexpected kernel BRK exception at EL1\n");
+		return -EFAULT;
+	}
+
+	return 0;
+}
+NOKPROBE_SYMBOL(brk_handler);
+
+int aarch32_break_handler(struct pt_regs *regs)
+{
+	u32 arm_instr;
+	u16 thumb_instr;
+	bool bp = false;
+	void __user *pc = (void __user *)instruction_pointer(regs);
+
+	if (!compat_user_mode(regs))
+		return -EFAULT;
+
+	if (compat_thumb_mode(regs)) {
+		/* get 16-bit Thumb instruction */
+		__le16 instr;
+		get_user(instr, (__le16 __user *)pc);
+		thumb_instr = le16_to_cpu(instr);
+		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
+			/* get second half of 32-bit Thumb-2 instruction */
+			get_user(instr, (__le16 __user *)(pc + 2));
+			thumb_instr = le16_to_cpu(instr);
+			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
+		} else {
+			bp = thumb_instr == AARCH32_BREAK_THUMB;
+		}
+	} else {
+		/* 32-bit ARM instruction */
+		__le32 instr;
+		get_user(instr, (__le32 __user *)pc);
+		arm_instr = le32_to_cpu(instr);
+		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
+	}
+
+	if (!bp)
+		return -EFAULT;
+
+	send_user_sigtrap(TRAP_BRKPT);
+	return 0;
+}
+NOKPROBE_SYMBOL(aarch32_break_handler);
+
+void __init debug_traps_init(void)
+{
+	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
+			      TRAP_TRACE, "single-step handler");
+	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
+			      TRAP_BRKPT, "BRK handler");
+}
+
+/* Re-enable single step for syscall restarting. */
+void user_rewind_single_step(struct task_struct *task)
+{
+	/*
+	 * If single step is active for this thread, then set SPSR.SS
+	 * to 1 to avoid returning to the active-pending state.
+	 */
+	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
+		set_regs_spsr_ss(task_pt_regs(task));
+}
+NOKPROBE_SYMBOL(user_rewind_single_step);
+
+void user_fastforward_single_step(struct task_struct *task)
+{
+	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
+		clear_regs_spsr_ss(task_pt_regs(task));
+}
+
+void user_regs_reset_single_step(struct user_pt_regs *regs,
+				 struct task_struct *task)
+{
+	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
+		set_user_regs_spsr_ss(regs);
+	else
+		clear_user_regs_spsr_ss(regs);
+}
+
+/* Kernel API */
+void kernel_enable_single_step(struct pt_regs *regs)
+{
+	WARN_ON(!irqs_disabled());
+	set_regs_spsr_ss(regs);
+	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
+	enable_debug_monitors(DBG_ACTIVE_EL1);
+}
+NOKPROBE_SYMBOL(kernel_enable_single_step);
+
+void kernel_disable_single_step(void)
+{
+	WARN_ON(!irqs_disabled());
+	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
+	disable_debug_monitors(DBG_ACTIVE_EL1);
+}
+NOKPROBE_SYMBOL(kernel_disable_single_step);
+
+int kernel_active_single_step(void)
+{
+	WARN_ON(!irqs_disabled());
+	return mdscr_read() & DBG_MDSCR_SS;
+}
+NOKPROBE_SYMBOL(kernel_active_single_step);
+
+void kernel_rewind_single_step(struct pt_regs *regs)
+{
+	set_regs_spsr_ss(regs);
+}
+
+/* ptrace API */
+void user_enable_single_step(struct task_struct *task)
+{
+	struct thread_info *ti = task_thread_info(task);
+
+	if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
+		set_regs_spsr_ss(task_pt_regs(task));
+}
+NOKPROBE_SYMBOL(user_enable_single_step);
+
+void user_disable_single_step(struct task_struct *task)
+{
+	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
+}
+NOKPROBE_SYMBOL(user_disable_single_step);