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// 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_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 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_regs_spsr_ss(struct pt_regs *regs)
{
regs->pstate |= DBG_SPSR_SS;
}
NOKPROBE_SYMBOL(set_regs_spsr_ss);
static void clear_regs_spsr_ss(struct pt_regs *regs)
{
regs->pstate &= ~DBG_SPSR_SS;
}
NOKPROBE_SYMBOL(clear_regs_spsr_ss);
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 int esr)
{
struct step_hook *hook;
struct list_head *list;
int retval = DBG_HOOK_ERROR;
list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
rcu_read_lock();
list_for_each_entry_rcu(hook, list, node) {
retval = hook->fn(regs, esr);
if (retval == DBG_HOOK_HANDLED)
break;
}
rcu_read_unlock();
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,
(void __user *)instruction_pointer(regs),
"User debug trap");
}
static int single_step_handler(unsigned long unused, unsigned int 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 int esr)
{
struct break_hook *hook;
struct list_head *list;
int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
rcu_read_lock();
list_for_each_entry_rcu(hook, list, node) {
unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
if ((comment & ~hook->mask) == hook->imm)
fn = hook->fn;
}
rcu_read_unlock();
return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
}
NOKPROBE_SYMBOL(call_break_hook);
static int brk_handler(unsigned long unused, unsigned int esr,
struct pt_regs *regs)
{
if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
return 0;
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